Information

Cells - Biology


Time

The following parts of this lab should be done first because they will require time after they are set up. They should be done in the order shown below.

  1. Osmosis in Potato Cells takes 60 minutes after the experiment is set up. Click the link or scroll to go to that section of the lab.
  2. An Artificial Cell takes 40 minutes after it is set up.
  3. Diffusion in a Liquid takes the rest of the lab period after it is set up.

After you have begun the three parts listed above, you should complete the rest of the lab (below

Introduction

All organisms are composed of cells. Cells are the smallest structures that are living; they are the unit of life. Two very different kinds of cells exist in nature. Prokaryotes are the simplest kind of organisms (example: bacteria). Their cells lack many of the structures (organelles) typically found in more complex cells. All other organisms contain cells that are considerably more complex. These organisms include all of the plants, animals, fungi, and protists.

We will look at prokaryotic cells in this exercise but we will examine details of the structure of eukaryotic cells.

The plasma membrane is vitally important in regulating the passage of materials into and out of the cell. We will see that small cells have a large surface to volume ratio, thus, more plasma membrane to service it's contents.

The plasma membrane is differentially permeable, that is, some molecules such as water can pass through but others cannot. We will study some characteristics that result from this property.

Examination of Prokaryotic Cells

The exercises below require the use of a microscope. Click here for instructions on using the microscope.

  1. Examine a slide of bacterial types under high power (400 X). The slide contains spherical cells (cocci), rod-shaped cells (bacilli), and spiral shaped cells (spirilla). Draw several cells. The rod-shaped bacteria on the slide are attached end-to-end forming threadlike filaments. If you look carefully, you can seed the individual cells that compose the filament. Write the magnification used next to your diagram. Note the size of these cells compared to eukaryotic cells.

  2. Cyanobacteria are photosynthetic prokaryotes and may be connected in chains or filaments. Examine a slide of Cyanobacteria such as Anabaena under high power (400X). Draw representative Cyanobacteria in your notebook.

Examination of Eukaryotic Cells

We will examine an organism called amoeba as an example of a eukaryotic cell.

  1. Prepare a slide of live Amoeba. Use a dropper to obtain a sample from the bottom of the culture jar. There may be a wheat seed on the bottom of the jar. Try to obtain a drop from the bottom near the seed. If live Amoeba are not available, observe a prepared slide of Amoeba.

  2. Identify the pseudopodia. If you are also viewing a prepared slide that has been stained, you should also be able to see the nucleus. Note that the cell is much larger than the prokaryotic cells (above) and is filled with numerous organelles. The functions of some of these organelles will be discussed later.

  3. Draw an Amoeba in your notebook and indicate the magnification used.

Observation of a Living Plant Cell

  1. Prepare a wet mount of an Elodea leaf. View the cell under low and high power. Use the fine focus to focus up and down on a cell. Cells above and below your cell may interfere with your viewing. Identify the cell wall, and chloroplasts. If your specimen is fresh, you should be able to see the chloroplasts moving within the cell.

  1. Notice that there are few chloroplasts in the center of the cell. This space is occupied by the central vacuole.

  2. Draw an Elodea cell and state the magnification used.

Below: Elodea 100X and 400X.

Animal Cells
  1. If you have not observed human cheek cells in a previous laboratory exercise prepare a wet mount by using the following procedure.

    Scrape the inside of your cheek with a toothpick and rub it on a dry slide.

    Add one drop of methylene blue to stain the cells. This will make them easier to see.

    Place a cover slip on the slide as described above and observe the cells under low power then high power.

  2. Identify the nucleus.

  3. How do these animal cells differ from the Elodea (plant) cells? See your drawings of typical plant and animal cells to help with the answer to this question.

  4. Draw a cheek cell.

Below: Human cheek cells 100X. Click on the photograph to view an enlargement.

Diffusion and Osmosis

Diffusion is the movement of molecules from an area of higher concentration to an area of lower concentration. The movement is due to molecular collisions, which occur more frequently in areas of higher concentration.

Diffusion

Diffusion in a Liquid
  1. Create a hypothesis for the experiment described below.

  2. Obtain a Petri dish and add enough water to cover the bottom.

  3. Place the dish on a ruler so that the metric scale crosses the center of the dish.

  4. Allow the water to remain still for one minute, then add a crystal of potassium permanganate to the center of the dish.

  5. Measure how far the molecules diffused after 10 minutes. Distance should be measured from the crystal to the edge of the purple area (or diameter of the purple area/2).

  6. Calculate the rate of diffusion per hour.

  7. Observe the dish at the end of the laboratory period. Did the potassium permanganate diffuse throughout the entire dish by the end of the laboratory period?

  8. After this part is set up, you should return to the top of this page and complete the rest of this lab.
Diffusion in a Gelatin

Several drops of dye have been added to tubes containing a clear gelatin.

  1. Obtain one of these tubes that was prepared during the past week and measure how far the dye diffused.

  2. Record the number of hours that the dye has been diffusing.

  3. Calculate the rate of diffusion per hour.

  4. Obtain a tube that had been prepared last semester. What happened?

Dye was added to the top tube 3 days before the photograph was taken. Dye was added to the middle tube 157 days prior to photographing and the bottom tube was 370 days. How does the rate of diffusion in a gelatin compare to your experiment with diffusion in water?

Osmosis

The center of cell membranes contains the nonpolar fatty acid tails of phospholipid molecules. Because of this large nonpolar area, charged particles and large polar molecules cannot diffuse across the membrane. Small polar molecules such as water can diffuse across the membrane.

Osmosis is the diffusion of water across a differentially permeable membrane (see "Diffusion" above).

It occurs when a solute (example: salt, sugar, protein, etc.) cannot pass through a membrane but the solvent (water) can. Water always moves from where it is most concentrated (has less solute) to where it is less concentrated.

In general, water moves toward the area with a higher solute concentration because it has a lower water concentration.

In the container on the left side of the diagram, water will enter the cell because it is more concentrated on the outside. In the center drawing, water is more concentrated inside the cell, so it will move out. If the solute concentration is the same inside as it is out, the amount of water that moves out will be approximately to the amount that moves in.

Osmotic pressure is the force of osmosis. In the diagram above, the cell on the left will swell. The pressure within the cell is osmotic pressure.

Artificial Cells

Dialysis tubing can be used to simulate the selective permeability of cell membranes and to demonstrate osmosis. Pores within the tubing restrict the passage of large molecules but allow water molecules to pass through. In biological membranes, large polar molecules such as cannot cross the polar region of the lipid bilayer but small molecules such as water can pass through. Sugar molecules are used in the experiment below because they are large and cannot pass through the tubing.

  1. Create a hypothesis for the experiment described below.

  2. Cut two pieces of dialysis tubing approximately 15 cm in length each.

  3. Moisten the tubes with water and then clamp one end. Plastic or foam clamps may be used. Instructions for using the foam clamps are below. Click an image to view an enlargement.

  1. Rinse the tubes under water so that they can be opened.

  2. Fill one tube 1/2 full with 50% molasses solution.

  3. Fill the other tube 1/2 full with deionized water.

  4. Clamp the other end of each tube. Be sure that you leave plenty of room in the tube for water to enter.

  5. Rinse each tube under water and let them drip for about 10 seconds to remove excess moisture.

  6. Place a plastic weighing tray on the scale and zero the scale. Weigh each tube to the nearest 0.1 g. Be sure to zero the scale and weighing tray before weighing the second tube. Do not place the bag directly on the metal weighing pan of the scale and do not drip liquids on the scale because this could damage the scale.

  7. Place the tube containing molasses in a beaker containing deionized water. The beaker should contain enough water to cover the tube.

  8. Place the tube containing deionized water in a beaker containing a concentrated sucrose (sugar) solution. Use enough sucrose solution to cover the tube.

  9. Weigh each tuber again after 10, 20, 30 and 40 minutes. Be sure to use a plastic weighing tray and to zero the scale before placing the tube on the weighing tray.

  10. Record your data in a table in your notebook.

  11. Plot your results using a graph in your notebook. If your notebook does not have a grid (is not quad-ruled or graph-ruled), you must use graph paper or a computer graphing program such as Excel (see Creating Graphs using Excel)

    A) Be sure that you put the independent variable on the X axis.

    B) A line graph is appropriate for continuous data. A bar graph is more appropriate for data that fall into categories with no particular order to the categories. In this case, time is continuous. We measured it in five increments but it is possible to have measurements between the five.

  12. Did the rate of gain appear to be constant? You can answer this question by seeing if the graph is a straight line.

  13. What do you predict would happen to the bag after one day?

Osmosis in Potato Cells
  1. Create a hypothesis for the experiment described below.

  2. Cut two strips of potato about the size of a French fry (approximately 5 mm X 5 mm X 50 mm).

  3. Put one of the strips in a small beaker that contains enough 10% NaCl to cover the potato.

  4. Put the other strip in a beaker that contains enough deionized water to cover the potato.

  5. Remove the strips from the beakers after about 60 minutes and examine the potatoes. Is one of them limp? Is one firm? Record your observations in your notebook.

  6. Explain your observations. Be to mention where the concentration of water molecules is greater (and salt is less) and where the concentration of water molecules is less (salt is greater).

Plasmolysis in Elodea
  1. Create a hypothesis for the experiment described below.

  2. Obtain a leaf of Elodea and place it on a blank microscope slide.

  3. Dry it with a paper, add a drop or two of 10% NaCl, and then cover it with a cover slip.
  4. Observe the cells under scanning and low power immediately after you prepare the slide.

  5. Let the slide sit for 10 minutes and observe the cells again. It may be helpful to use a brighter light to view the cells. As the cell shrinks, the chloroplasts will appear to clump together.

  6. Describe what happened to the cells.

  7. Why did this happen? To help you answer this question, consider where the concentration of water molecules is greatest and where it is least.


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About this course

The cell is a powerful case study to help us explore the functional logic of living systems. All organisms, from single-celled algae to complex multicellular organisms like us, are made up of cells. In this course, you will learn the how and why of biology by exploring the function of the molecular components of cells, and how these cellular components are organized in a complex hierarchy.

This course is designed to explore the fundamentals of cell biology. The overarching goal is for learners to understand, from a human-centered perspective, that cells are evolving ensembles of macromolecules that in turn form complex communities in tissues, organs, and multicellular organisms.

We will focus, in particular, on the mitochondrion, the organelle that powers the cell. In this context, we will look at the processes of cell metabolism. Finally, we will examine the F1F0 ATP synthase, the molecular machine that is responsible for the synthesis of most of the ATP that your cells require to do work. To underscore the importance of cell biology to our lives, we will address questions of development and disease and implications of science in society.

By the end of four weeks, we hope learners will have a deep intuition for the functional logic of a cell. Together we will ask how do things work within a cell, why do they work the way they do, and how are we impacted?

Join us as we explore the extraordinary and wonderfully dynamic world of the cell.


Research Interests

The laboratory of Structural Cell Biology aims to understand the molecular mechanisms governing specialized cell shapes, such as those of neurons, activated immune cells or platelets and certain cancer cells. We visualize the key factors determining different cell morphologies using in situ cellular cryo-electron tomography in combination with interdisciplinary techniques such as single-particle cryo-EM, X-ray crystallography, in vitro reconstitution and light microscopy. The lab was initiated in 2012 at the Max Planck Institute of Biochemistry in Martinsried and is relocated to the NIH (NIAMS/NHLBI joint appointment) in 2020. Neuronal cell formation Neuronal cell formation is a distinctive example of specialized cells. To connect the distal end of the nervous system to the central brain, cells are shaped in an extremely polarized fashion, with a long stem part, axon, shaped by microtubules. To create a neural network, individual cells form branching points from the axon as connection points. At the axon branching points, membrane receptors respond to extra-cellular cues, starting a directed signaling cascade. This action results in the remodeling of the actin and microtubule cytoskeleton. Dynamic crosstalk of membrane, actin and microtubules are implicated in axon branch formation. We aim to elucidate the molecular action governing this cellular event. Wound healing and immunological cell formation Platelets and immune cells undergo dynamic morphological changes during activation to adhere to each other or to specific target antigens. Although the molecular bases of the actions are similar to the ones of neuronal cell formation, the morphological outcome can vary drastically. For example, activated platelets produce spikes of filopodia on the surface, resembling the shape of a sunflower. We aim to understand the molecular re-organization during the activation process. We further study signaling defects that cause immunodeficiencies or problems with wound healing to identify molecular clues for cellular defects. Bottom-up reconstitution the underlying molecular mechanisms and the signaling processes governing cell shape formation are challenging to elucidate within a cell due to their complexity and diverse crosstalk with other pathways. To precisely understand the molecular functions of key components, we are taking a bottom-up approach to reconstitute and investigate the macromolecular machinery that can mimic cell shape formation processes using biophysical and structural biological methods. The functional relevance learned from the in vitro reconstitution analysis is then validated inside cells by mutagenesis and in situ analysis.


Cell biology

Big scientific encyclopedia "Cell biology" - meiosis and mitosis, cytokines, cellular processes, signaling, movement, growth factors, etc.

Cell biology (also cellular biology or cytology) - the science of cells. The subject of cytology is the cell as a structural and functional unit of life. The tasks of cytology include the study of the structure and functioning of cells, their chemical composition, functions of individual cellular components, processes of cell reproduction, adaptation to environmental conditions, study of the structural features of specialized cells, etc. Research in cellular biology is interconnected to other fields such as genetics, molecular genetics, biochemistry, molecular biology, medical microbiology, immunology, and cytochemistry.

Organelles are permanent intracellular structures that differ in structure and perform various functions. Organelles are subdivided into membrane (two-membrane and one-membrane) and non-membrane. The two-membrane components are plastids, mitochondria and the cell nucleus. The organelles of the vacuolar system are one-membrane organelles - the endoplasmic reticulum, the Golgi complex, lysosomes, vacuoles of plant and fungal cells, pulsating vacuoles, etc. Nonmembrane organelles include the ribosomes and the cell center, which are constantly present in the cell.

Mitochondria are integral components of all eukaryotic cells. They are granular or threadlike structures. Mitochondria are bounded by two membranes - the outer and the inner. The outer mitochondrial membrane separates it from the hyaloplasm. The inner membrane forms many invaginations inside the mitochondria - the so-called cristae.

Mitosis is a method of cell division in which genetic material (chromosomes) is distributed equally between new (daughter) cells. It starts by dividing the core into two children. The cytoplasm is similarly divided. The processes that take place from one division to another are called the mitotic cycle.

Meiosis is a stage in the formation of germ cells consists of two successive divisions of the original diploid cell (containing two sets of chromosomes) and the formation of four haploid germ cells, or gametes (containing one set of chromosomes).

The cytoskeleton, a set of filamentous protein structures - microtubules and microfilaments that make up the musculoskeletal system of the cell. The cytoskeleton is possessed only by eukaryotic cells it is absent in the cells of prokaryotes (bacteria). The cytoskeleton gives the cell a certain shape even in the absence of a rigid cell wall. It organizes the movement of organelles in the cytoplasm. The cytoskeleton is easily rearranged, providing, if necessary, a change in the shape of the cells.

Amino acids are the structural components of proteins. Proteins, or proteins, are biological heteropolymers, the monomers of which are amino acids. About 200 amino acids are known to be found in living organisms, but only 20 of them are part of proteins. These are basic, or protein-forming (proteinogenic), amino acids.

By their chemical nature, enzymes are simple or complex proteins their molecules may include a non-protein part - a coenzyme. The mechanism of action of enzymes is to reduce the activation energy of the catalyzed reaction. This is achieved by attaching the enzyme to the reacting substances and forming an intermediate complex with them, as a result of which the energy threshold of the reaction decreases and the probability of its proceeding in the desired direction sharply increases.

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Cell Biology: An Overview☆

Abstract

Cell biology is the study of the composition, organization and function of cells, of which all living matter is composed. The unicellular organisms made up mostly of prokaryotes (bacteria and archaea) are architecturally distinguishable from the eukaryotes in that they lack membrane bound organelles, which in turn gives rise to many distinguishing functions. Nevertheless, all cells are composed of the same general building blocks, and all are able to generate and use energy -rich compounds, to reproduce themselves and to sense and respond to their environment. The diversity in cell structure and activity that has accompanied evolution provides a rich tapestry for understanding these basic units of life.


Glial Cells Function

The function of glial cells was previously thought to be a structural one, which is why they were named glia (Greek for glue) by nineteenth-century scientists. This function is now considered to be a minor one.

Glial cells function as modulators of the CNS and PNS environments they increase and decrease activity within the synapses by regulating neurotransmitter, oxygen, and ion uptake they also aid nerve injury recovery. Specific roles are carried out by the different glial cell types.

Glial cell abnormalities are associated with various pathologies including autoimmune disorders and cancer. This supports research that shows certain glia types are heavily involved in the immune system and inflammatory responses.

The macroglia (larger glial cells) insulate, protect, and help neurons to develop and migrate. Microglia (smaller types of glia) have phagocytic properties, digesting foreign particles. They even contribute to nervous tissue immune responses and repair processes as they can migrate to areas of damage. Furthermore, micro- and macroglia work together to ensure optimal neuron function and neurotransmission through the synapses.


Cell Biology Basics

Cell biology assays are used with cells grown in vitro to help researchers answer questions about the structure and function of cells and cellular components. Techniques used include methods to measure metabolic activity, cell signaling pathways, and regulation of gene expression, and to characterize the physiological changes associated with cell death. Assays for cell biology detect and measure these fundamental cellular processes and are used across many research, applied science and drug discovery applications.

Cell biology assays can be used with cellular model systems including :

  • monolayer cell cultures – any cell type grown on a dish. Cell types include cells that grow in a suspension or adhered to the surface of the dish
  • 3D microtissues – cells grown in a spheroid shape, using various means to create the 3D structure
  • primary cells – cells isolated directly from an organism
  • cancer and other immortalized cell lines – cell lines that grow continuously in vitro due to aberrant signaling mechanics
  • stem cells – cells isolated in a variety of ways that retain the ability to differentiate into multiple different cell types

Many cell-based and biochemical assays use bioluminescence to detect specific cellular events. Bioluminescence chemistries are increasingly popular in a variety of bioanalytical methods because they can deliver 10- to 1,000-fold higher assay sensitivity than fluorescence assays. This greatly increased sensitivity can substantially improve assay performance when applied in complex biological samples common to cell biology applications. Bioluminescence chemistry can be applied to multiple assay types in cell biology research, including reporter assays where genetic content is delivered using transfection-based methods, and cell signaling, cell viability and cytotoxicity assays that do not require cell engineering.


Cell Biology

The much-anticipated 3rd edition of Cell Biology delivers comprehensive, clearly written, and richly illustrated content to today’s students, all in a user-friendly format. Relevant to both research and clinical practice, this rich resource covers key principles of cellular function and uses them to explain how molecular defects lead to cellular dysfunction and cause human disease. Concise text and visually amazing graphics simplify complex information and help readers make the most of their study time.

The much-anticipated 3rd edition of Cell Biology delivers comprehensive, clearly written, and richly illustrated content to today’s students, all in a user-friendly format. Relevant to both research and clinical practice, this rich resource covers key principles of cellular function and uses them to explain how molecular defects lead to cellular dysfunction and cause human disease. Concise text and visually amazing graphics simplify complex information and help readers make the most of their study time.


History of Cell Biology

The cell theory, or cell doctrine, states that all organisms are composed of similar units of organization, called cells. The concept was formally articulated in 1839 by Schleiden & Schwann and has remained as the foundation of modern biology. The idea predates other great paradigms of biology including Darwin’s theory of evolution (1859), Mendel’s laws of inheritance (1865), and the establishment of comparative biochemistry (1940).

First Cells Seen in Cork

While the invention of the telescope made the Cosmos accessible to human observation, the microsope opened up smaller worlds, showing what living forms were composed of. The cell was first discovered and named by Robert Hooke in 1665. He remarked that it looked strangely similar to cellula or small rooms which monks inhabited, thus deriving the name. However what Hooke actually saw was the dead cell walls of plant cells (cork) as it appeared under the microscope. Hooke’s description of these cells was published in Micrographia. The cell walls observed by Hooke gave no indication of the nucleus and other organelles found in most living cells. The first man to witness a live cell under a microscope was Anton van Leeuwenhoek, who in 1674 described the algae Spirogyra. Van Leeuwenhoek probably also saw bacteria.

Formulation of the Cell Theory

In 1838, Theodor Schwann and Matthias Schleiden were enjoying after-dinner coffee and talking about their studies on cells. It has been suggested that when Schwann heard Schleiden describe plant cells with nuclei, he was struck by the similarity of these plant cells to cells he had observed in animal tissues. The two scientists went immediately to Schwann’s lab to look at his slides. Schwann published his book on animal and plant cells (Schwann 1839) the next year, a treatise devoid of acknowledgments of anyone else’s contribution, including that of Schleiden (1838). He summarized his observations into three conclusions about cells:

  1. The cell is the unit of structure, physiology, and organization in living things.
  2. The cell retains a dual existence as a distinct entity and a building block in the construction of organisms.
  3. Cells form by free-cell formation, similar to the formation of crystals (spontaneous generation).

We know today that the first two tenets are correct, but the third is clearly wrong. The correct interpretation of cell formation by division was finally promoted by others and formally enunciated in Rudolph Virchow’s powerful dictum, Omnis cellula e cellula,: “All cells only arise from pre-existing cells”.

Modern Cell Theory

  1. All known living things are made up of cells.
  2. The cell is structural & functional unit of all living things.
  3. All cells come from pre-existing cells by division. (Spontaneous Generation does not occur).
  4. Cells contains hereditary information which is passed from cell to cell during cell division.
  5. All cells are basically the same in chemical composition.
  6. All energy flow (metabolism & biochemistry) of life occurs within cells.

As with the rapid growth of molecular biology in the mid-20th century, cell biology research exploded in the 1950’s. It became possible to maintain, grow, and manipulate cells outside of living organisms. The first continuous cell line to be so cultured was in 1951 by George Otto Gey and coworkers, derived from cervical cancer cells taken from Henrietta Lacks, who died from her cancer in 1951. The cell line, which was eventually referred to as HeLa cells, have been the watershed in studying cell biology in the way that the structure of DNA was the significant breakthrough of molecular biology.

In an avalanche of progress in the study of cells, the coming decade included the characterization of the minimal media requirements for cells and development of sterile cell culture techniques. It was also aided by the prior advances in electron microscopy, and later advances such as the development of transfection methods, the discovery of green fluorescent protein in jellyfish, and discovery of small interfering RNA (siRNA), among others.

The study of the structure and function of cells continues today, in a branch of biology known as cytology. Advances in equipment, including cytology microscopes and reagents, have allowed this field to progress, particularly in the clinical setting.

1595 – Jansen credited with 1st compound microscope
1655 – Hooke described ‘cells’ in cork.
1674 – Leeuwenhoek discovered protozoa. He saw bacteria some 9 years later.
1833 – Brown descibed the cell nucleus in cells of the orchid.
1838 – Schleiden and Schwann proposed cell theory.
1840 – Albrecht von Roelliker realized that sperm cells and egg cells are also cells.
1856 – N. Pringsheim observed how a sperm cell penetrated an egg cell.
1858 – Rudolf Virchow (physician, pathologist and anthropologist) expounds his famous conclusion: omnis cellula e cellula, that is cells develop only from existing cells [cells come from preexisting cells]
1857 – Kolliker described mitochondria.
1879 – Flemming described chromosome behavior during mitosis.
1883 – Germ cells are haploid, chromosome theory of heredity.
1898 – Golgi described the golgi apparatus.
1938 – Behrens used differential centrifugation to separate nuclei from cytoplasm.
1939 – Siemens produced the first commercial transmission electron microscope.
1952 – Gey and coworkers established a continuous human cell line.
1955 – Eagle systematically defined the nutritional needs of animal cells in culture.
1957 – Meselson, Stahl and Vinograd developed density gradient centrifugation in cesium chloride solutions for separating nucleic acids.
1965 – Ham introduced a defined serum-free medium. Cambridge Instruments produced the first commercial scanning electron microscope.
1976 – Sato and colleagues publish papers showing that different cell lines require different mixtures of hormones and growth factors in serum-free media.
1981 – Transgenic mice and fruit flies are produced. Mouse embryonic stem cell line established.
1995 – Tsien identifies mutant of GFP with enhanced spectral properties
1998 – Mice are cloned from somatic cells.
1999 – Hamilton and Baulcombe discover siRNA as part of post-transcriptional gene silencing (PTGS) in plants


Watch the video: Biology - Intro to Cell Structure - Quick Review! (January 2022).