3.0 Cell Structure Flashcards
What is a light microscope used for?
Observing living and dead organisms
What are the pros and cons of a light microscope?
Pros: cheap, portable, can view live specimens
Cons: low resolution, low magnification
What is the formula to calculate magnification size?
Magnification = image size / actual size
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 points as seperate
Why do electron microscopes give a clearer image than light microscopes?
The wavelength of light limits resolution as it is long. Electron microscopes have a higher resolution due to shorter wavelength of electrons.
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, buffered, isotonic solution, why?
Cold - reduces enzyme activity
Isotonic - prevents bursting or shrinking due to osmosis
Buffered - prevent denaturing of organelles
What are the two stages of cell fractionation?
Homogenisation and ultracentrifugation
What is homogenisation?
Breaking up the cells in a blender to release the organelles into the homogenate
What is the homogenate?
Fluid contains cell organelles
Why is the homogenate filtered before ultracentrifugation?
Remove whole cells and large debris
How is ultracentrifugation carried out?
Homogenate loaded into a centrifuge which spins the solution until the heaviest particles collect at the bottom of the tube. Remaining fluid collected and spun again at a higher speed. Process repeated as lighter organelles come out at higher speeds
What is the fluid collected from the centrifuge called?
Supernatant
In what order do organelles come out the centrifuge?
- Nuclei
- Chloroplasts/ mitochondria
- Lysosomes
What is a transmission electron microscope used for?
Observing the internal ultra structure 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?
- Must be in a vacuum
- Complex preparation
- Specimen must be thin
- May create artifacts
What is the difference between a TEM and a SEM?
TEM sends a beam of electrons through the specimen while a SEM bounces electrons off the surface
What is the difference between light and electron microscopes?
Light uses lenses to focus a beam of light while an electron uses a beam of electrons
What is the difference in images produced by a SEM and TEM?
TEM gives a 2D image while a SEM gives a 3D image
What is an eyepiece graticule?
A small ruler fitted to a light microscope’s eyepiece. it must be calibrated using a stage micrometer before being used to measure specimens
What is a sage micrometer?
A millimetre long ruler etched onto a slide, it has 100 division, each of 10 micrometers, it is used to calibrate the eyepiece graticule
What is a cells ultra structure?
The organelles that make up the cell
Describe the structure of the nucleus?
Surrounded by a double membrane (nuclear envelope) Contains chromosomes within the nucleolus, contains a jelly-like substance called the nucleoplasm
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?
Spherical region of the nucleus which produces ribosomes
What is the structure of the nuclear envelope?
A double membrane embeded with channel
proteins forming pores. Continuous with
endoplasmic reticulum.
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 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 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?
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, producing 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 the cell wall?
Present in plants, algae and fungi only.Made of polysaccherides, 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 is the structure and function of the vacuole?
It cointains salts, sugars, amino acids, waste and sometimes pigments.
What is the function of a plant’s vacuole?
Provides structure to plants by making cells turgid. Temporary food store. Provides colour to plants attracting insects.
What is the structure and function of the plasma membrane?
Phospholipid bilayer, cholesterol, proteins, glycoproteins, glycolipids. Separates cell contents from external environment. Controls what enters and leaves the cell. Identifies cell as self. Acts as a receptor for various chemicals. site of chemical reactions.
What kind of organisms have specialised cells?
Multicellular
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?
Increased efficiency
In what basic way are specialised cells adapted to perform their role?
They have more or fewer of certain organelles and structures to suit it’s role.
How can the first few cells that make an embryo be described?
Identical
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. Cilliated 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 gentic information for replication of bacteria.
What are 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 differnt from pro to eukaryotes?
Prokaryotes has an area of DNA, Eukaryotes have a distinct nucleus with nuclear envelope.
How is the structure of DNA different from pro 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 photosythetic organelles different from pro to eukaryotic cells?
some prokaryotes contain chlorophyll in their memranes. 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?
Prokaryotes cell walls are made of meurin (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 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 are the 2 methods of cell division?
Mitosis and meiosis
What is created through mitosis?
What is created through mitosis?
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 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
And
What happens during cytokinesis?
The cells separates from one another. The membrane pinches in to fuse with itself causeing 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 - New cell wall forms in the middle of the cell dividing it into 2 identical daughteer 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 create al 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.
What is the name given to the different types of tumour?
Benign or malignant (cancerous).
What is the basic difference between a benign and a malignant tumour?
A benign tumour grows slowly and is kept in one place, not typically life threatening. A malignant tumour grows quickly and will spread around the body, more likely to be life threatening.
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 hapens 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 to normal body cells. Typically they die or are destroyed.
If damaged cells created the genetic mutation survive, what could happen?
They could clone themselves and form either benign or malignant tumours.
