Chapter 3 Cell Structure Flashcards
What is a cell’s ultrastructure?
The organelles that make up the cell.
What are the main structures of eukaryotic cells?
Nucleus; cell-surface membrane; mitochondria; Golgi apparatus and golgi sacs; smooth endoplasmic reticulum; rough endoplasmic reticulum; ribosomes. Chloroplasts (in plants and algae); cell wall (plants, algae and fungi); cell vacuole (plants).
What is the structure of the nucleus?
Surrounded by a double membrane (the nuclear envelope). Contains chromosomes (Protein bound linear DNA); nucleoplasm; an 1 or more nucleoli.
What is the function of the nucleus?
Stores the human genome, controls the cell by providing instructions for protein synthesis.
What is the structure and function of the nucleolus?
The nucleolus is a spherical region of the nucleus that produces ribosomes. There may be multiple in one nucleus.
What is the structure of the nuclear envelope?
A double membrane embedded with channel proteins forming pores. Continuous with endoplasmic reticulum.
What is the function of the nuclear envelope?
Separates the nucleus from the rest of the cell. Pores allow ribosomes and mRNA to leave the nucleus.
What is the structure of the rough endoplasmic reticulum (RER)?
A system of fluid filled membranes studded with ribosomes. Continuous with the nuclear membrane. Large surface area formed by folding.
What is the function of the rough endoplasmic reticulum (RER)?
Synthesis of proteins and glycoproteins. Provides a pathway to transport materials, especially proteins.
What is the structure of the smooth endoplasmic reticulum (SER)?
A system of fluid filled membranes. No ribosomes.
What is the function of the smooth endoplasmic reticulum (SER)?
Synthesises, stores and transports lipids and carbohydrates.
What is the structure of the Golgi apparatus?
A stack of flattened membrane bound sacs called cisternae.
What is the function of the Golgi apparatus?
Vesicles from the ER join, bringing their products. Here they are modified, by adding sugar to make glycoproteins, adding lipids to form glycolipids. It makes secretory enzymes; secretes carbohydrates; transports and modifies lipids; creates lysosomes.
What is the structure of the ribosomes?
2 subunits, large and small. Made of rRNA . 2 types 80s found in eukaryotes, 70s found in prokaryotes.
What is the function of the ribosomes?
Proteins synthesised here.
What is the structure of the mitochondria?
Double membrane bound. Inner membrane folded into cristae within a fluid filled matrix. Contain own DNA and 70s ribosomes.
What is the function of the mitochondria?
Site of aerobic respiration, releasing ATP.
What is the structure of the lysosomes?
Membrane bound sacs containing hydrolytic (digestive) enzymes and lysozymes.
What is the function of the lysosomes?
Break down old organelles and foreign matter for reuse. Hydrolyse ingested material. Release enzymes to destroy other substances. Break down the cell after cell death (autolysis).
What is the structure of the chloroplasts?
Double membrane bound. Inner membrane forms flat discs filled with chlorophyll called thylakoids, in stacks called granum. These are surrounded by a fluid matrix called the stroma. Contain own DNA and 70s ribosomes.
What is the function of the chloroplasts?
Site of photosynthesis.
What is the structure of the cell wall?
Present in plants, algae and fungi only. Made of polysaccharides, bundles of cellulose fibres in plants, chitin in fungi.
What is the function of the cell wall?
Provides support and strength, maintaining the cell’s shape. prevents the cell from bursting when turgid. Permeable to allow solutions through.
Which structures are involved in the production of proteins?
Nucleus; RER; transport vesicle; Golgi apparatus
What is the structure of the vacuole?
Fluid filled membrane sac. In a plant the membrane is called the tonoplast.
What does the vacuole contain?
It contains salts, sugars, amino acids, waste and sometimes pigments.
What is the function of a plant’s vacuole?
The vacuole provides structure to plants by making cells turgid. It acts as a temporary food store and provides colour to plants attracting insects.
Describe the structure of the plasma membrane.
The plasma membrane is made up of a phospholipid bilayer, cholesterol, proteins, glycoproteins, glycolipids.
Give 5 functions of the plasma membrane?
- Separates cell contents from external environment.
- Controls what enters and leaves the cell.
- Identifies the cell as self.
- Acts as a receptor for various chemicals.
- Site of chemical reactions.
What kind of organisms have specialised cells?
Multicellular organisms
Why do multicellular organisms have specialised cells?
So that specific functions can be performed
What is the hierarchy of organisation in terms of cells in an organism?
Cells -> tissues -> organs -> organs systems -> organism.
Why are the cells of an organism grouped into tissues, organs, etc?
For increased efficiency.
In what basic way are specialised cells adapted to perform their role?
They have more or fewer of certain organelles, structures and biological molecules to suit its role.
How can the first few cells that make an embryo be described?
They are identical (embryonic stem cells).
What happens to the embryonic cells as it develops?
They become specialised to perform specific roles.
All body cells of an organism arise by mitotic division, they are identical. How do they become specialised and different?
Certain genes are switched on (expressed) and certain genes are not.
What is a tissue?
A group of similar cells working together to perform a specific function.
Why are cells grouped into tissues?
This increases the working efficiency.
Describe epithelial tissue.
A sheet of cells that typically line organs. They are protective and/or secretory (release substances). E.g. thin flat cells of the alveoli aid diffusion. Ciliated epithelial tissue of trachea moves mucus.
What is an organ?
A collection of tissues, coordinated to perform specific functions
What is an organ system?
A group of organs working together as a single unit.
What is the difference between prokaryotic and eukaryotic cells?
Eukaryotic cells are larger and have a membrane bound nucleus. Prokaryotic cells are smaller and have no nucleus or nuclear envelope.
What are the main structures of bacterial cells?
Cell wall; capsule; cell-surface membrane; circular DNA; plasmids.
What is the role of the cell wall in bacteria?
Physical barrier to some substances, protects against mechanical damage and osmotic lysis.
What is the role of the capsule in bacteria?
Made of mucilaginous slime, it protects against other cells and allows bacteria to stick together for protection.
What is the role of the cell-surface membrane in bacteria?
Differentially permeable, controls entry and exit of chemicals.
What is the role of circular DNA in bacteria?
It contains the genetic information for replication of bacteria.
What is the role of plasmids in bacteria?
Possess genes that may aid survival. E.g. enzymes to break down antibiotics.
How is the organisation of DNA different from pro to eukaryotes?
Prokaryotes have an area of DNA, Eukaryotes have a distinct nucleus with a nuclear envelope.
How is the structure of DNA different in prokaryotes to eukaryotes?
Prokaryotic DNA is not associated with proteins. Eukaryotic DNA is associated with proteins called histones.
How are plasmids different from pro to eukaryotes?
Prokaryotes have rings of DNA called plasmids. Eukaryotes do not have plasmids.
How are organelles different from pro to eukaryotes?
Prokaryotes do not have membrane bound organelles, eukaryotes do.
How are photosynthetic organelles different from pro to eukaryotic cells?
Some prokaryotes contain chlorophyll in their membranes. Eukaryotes have chloroplasts (plants and algae).
How do ribosomes differ between pro and eukaryotes?
Prokaryotes contain 70s ribosomes. 80s ribosomes are found in eukaryotes.
How do cell walls vary between pro and eukaryotes?
Prokaryotic cell walls are made of murein (peptidoglycan). When present in eukaryotes they are cellulose (or chitin in fungi).
How does the capsule vary from pro to eukaryotes?
Prokaryotes have a mucilaginous outer layer. Eukaryotes do not.
How are viruses described?
A-cellular non-living particles.
What range of sizes are viruses?
Generally between 20-300 nm.
What is the basic structure of a virus?
Nucleic acids (DNA or RNA) contained within a protein coat called a capsid. Capsid contains attachment proteins. Occasionally there is an extra lipid coat surrounding the virus.
Where do viruses reproduce?
Within host cells.
What do attachment proteins allow the virus to do?
Allows the virus to identify itself and attach to a host cell.
What is a light microscope used for?
Observing living and dead specimens.
What are the pros and cons of a light microscope?
Pros: Cheap, portable, easy to use, can study living specimens.
Cons: Limited magnification, poor resolution.
What is the formula to calculate magnification?
Magnification = Image size / Actual size
What is the formula to calculate actual object size?
Actual size = Image size / Magnification
How do we work out image size?
Use a ruler and measure the image.
What is magnification?
A measure of how much larger the image of a specimen looks under the microscope.
What is resolution?
The ability to distinguish between two adjacent individual points as separate.
What resolution are light microscopes limited to?
0.2 micrometres
Why do electron microscopes give a clearer image than light microscopes?
The wavelength of light limits resolution to 0.2 micrometres. The wavelength of electrons allows a resolution of 0.1 nanometers.
By which process are large quantities of cell organelles collected?
Cell fractionation.
What is cell fractionation?
The process of breaking up cells to separate out the organelles.
The tissues to be fractionated are stored in a cold, osmotically balanced buffer, why?
Cold - reduces enzyme activity, breaking down organelles.
Equal water potential, prevents bursting or shrinking due to osmosis.
Buffered to prevent pH fluctuations altering organelle and enzyme activity.
What are the two stages of cell fractionation?
Homogenisation and ultracentrifugation
What is homogenisation (during cell fractionation)?
Breaking up of cells in a blender. This releases the organelles into the homogenate.
What is homogenate (part of cell fractionation)?
Fluid containing cell organelles, prior to ultracentrifugation.
Why is the homogenate filtered prior to ultracentrifugation? (cell fractionation)
To remove whole cells and large debris.
How is ultracentrifugation carried out? (cell fractionation)
The homogenate filtrate is loaded into a centrifuge which spins the solution until the heaviest particles collect at the bottom of the tube. This remaining fluid is collected and spun at a higher speed. This continues collecting progressively lighter material using higher speeds.
What is the fluid collected from the centrifuge called?
Supernatant.
What is the solid left in the centrifuge tube after the supernatant has been removed, called?
The remaining sediment is known as a pellet.
List the cell organelles in order of density
- Nuclei
- Mitochondria and Chloroplasts
- Microsomes (RER and other membranes)
- Ribosomes
What is a transmission electron microscope used for?
Observing the internal ultrastructure of cells under high magnification and resolution
What is a scanning electron microscope used for?
Viewing the surface of objects under high magnification and resolution
What are the limitations of a TEM?
Subject must be in a vacuum, so no living specimens; Complex preparation; No colour; Specimen must be extremely thin; Preparation of specimen may create artefacts.
What are TEM artefacts?
Things created during sample preparation. They can be mistaken for cellular components.
What is the difference between a transmission and scanning electron microscopes?
TEM sends a beam of electrons through the specimen, the SEM bounces electrons off the surface.
What is the difference between light and electron microscopes?
Light microscopes use lenses to focus a beam of light. Electron microscopes use a beam of electrons, focused by magnets.
What is the resolving power of a TEM compared to a SEM?
TEM = 0.1nm; SEM = 20nm
What is the difference in images between TEM and SEM?
TEM gives a 2D image of the contents of a cell. SEM gives a 3D image of the surface of an object.
What is an eyepiece graticule?
A small ruler fitted to a light microscope’s eyepiece. It must be calibrated using a stage micrometre before being used to measure specimens. Each lens needs to be calibrated individually.
What is a stage micrometre?
A millimetre long ruler etched onto a slide. It has 100 divisions, each of 0.01mm or 10 micrometres. It is used to calibrate the eyepiece graticule
How is the eyepiece graticule calibrated?
- The eyepiece graticule and stage micrometre are lined up.
- The number of divisions that match up are compared.
- The length of 1 eyepiece division to be calculated.
What are the maximum resolutions of the different microscopes?
Light: 200 nm; SEM: 20 nm; TEM: 0.1 nm.
What are the 2 methods of cell division?
Mitosis and meiosis
What is created through mitosis?
2 genetically identical daughter cells. They have the same number of chromosomes as the parent cell.
What is created through meiosis?
4 genetically unique daughter cells. They each have half the number of chromosomes as the parent cell.
What is the stage of the cell cycle in which the cell is not dividing?
Interphase.
What are the main stages of mitosis?
Prophase, metaphase, anaphase and telophase & cytokinesis.
Describe the main events of prophase
Nuclear envelope breaks down; chromosomes condense; nucleolus disappears; spindle fibres start to form spindle apparatus which draws chromosomes to the centre of the cell.
How is prophase different between animals and plants?
In animals the 2 centrioles move the poles of the cell. Plants do not have centrioles.
Describe the main events of metaphase.
Chromosomes are seen to be made of two identical chromatids. They line up along the equator (metaphase plate); microtubules attach to centromeres pulling the chromosomes along the spindle apparatus.
Describe the main events of anaphase
Sister chromatids pulled to opposite poles of the cell by shortening tubulin spindle fibres. The chromatids are now called chromosomes. This phase can be stopped by chemicals which destroy spindle fibres.
Where does the energy for anaphase come from?
Mitochondria which surround the spindle fibres.
Describe the main events of telophase
Nuclear envelope reforms around each set of chromosomes; Chromosomes relax, and disappear leaving widely spread out chromatin; nucleolus reappears.
What happens during cytokinesis?
The cells separate from one another. The membrane pinches in to fuse with itself causing the cytoplasm to divide.
What is the name given to cell division in prokaryotes?
Binary fission.
What are the main stages of binary fission?
1 - The circular DNA replicates and attaches to the cell membrane.
2 - Plasmids replicate.
3 - The cell membrane pinches in between the DNA to divide the cytoplasm.
4 - A new cell wall forms in the middle of the cell dividing it into 2 identical daughter cells.
Why do viruses not undergo cell division?
They are not living.
How do viruses replicate?
They attach to the cell using attachment proteins. It then injects genetic information into the cell, whose metabolic reaction creates all the parts necessary to create new viruses.
What are the 3 main stages of the cell cycle?
Interphase, nuclear division and division of cytoplasm (cytokinesis).
What is happening during interphase?
During interphase, the DNA is being replicated so that there is a copy for each of the 2 daughter cells. Organelles are also being replicated.
How are tumours linked to cell division?
Tumours are caused by uncontrolled cell division.
Why do cells replicate by mitosis?
To increase the size of tissues, ( growth); or to replace dead or damaged cells (repair).
What affects the rate of cell division?
The environment, growth factors and 2 genes.
What happens if the genes controlling cell division are damaged (mutated).
Uncontrolled mitosis can occur.
If uncontrolled mitosis due to mutation occurs, how does this affect the cells being created?
They are usually structurally and functionally different from normal body cells. Typically they die or are destroyed.
