2.1 CELL STRUCTURE Flashcards
What is a eukaryotic cell?
The DNA has a nucleus, and it has membrane bound organelles.
What is a prokaryotic cell?
The DNA is free in the cytoplasm and it has no membrane bound organelles.
What is the structure of the nucleus?
- Nuclear envelope membrane.
- Nuclear pores, controls what come in and out of nucleus.
- Nucleoplasm to make rRNA.
What is the function of the nucleus?
- Site of protein synthesis.
- Contains genetic information.
- Makes ribosomes.
What is the structure of the mitochondria?
- Double layer membrane controlling what enters and leaves.
- Membranes folded over to form cristae that increase SA.
- Matrix of biological molecules.
What is the function of mitochondria?
- Site of aerobic respiration.
- Produces ATP for respiration.
What is the structure of the chloroplast?
- Double membrane to control entry and exit.
- Have discs of membrane called thylakoids.
- Many thylakoids together form the grana to increase SA.
- Stroma of biological molecules (matrix).
What is the function of chloroplasts?
- Site of photosynthesis
- Stroma provides glucose for photosynthesis.
What is the structure of the Golgi apparatus?
Stacks of membranes with vesicles on them. (cisternae)
What is the function of the Golgi apparatus?
- Modifies and packages proteins.
- Forms lysosomes.
- Makes glycoproteins.
- Lipids come here to get modified, bind to vesicles, and the leave the apparatus.
What is the structure of a lysosome?
- Single layer membrane
- Simple sac filled with lysozyme, digestive enzymes.
What is the function of a lysosome?
- Breaks down cells after death.
- Releases digestive enzymes by exocytosis.
- Hydrolyses digested cell.
What is the structure of the endoplasmic reticulum?
- 3d sheets of membrane, forming the cisternae.
Rough: has ribosomes on the surface
What is the function of rough endoplasmic reticulum?
Site of protein-synthesis.
What is the function of smooth endoplasmic reticulum?
Site of lipid-synthesis
What is the structure of ribosomes?
Has two subunits, and is formed by the combination of rRNA and proteins.
What is the function of ribosomes?
Site of translation where:
Large sub-unit: holds the amino acid binding site.
Small sub-unit: holts the mRNA binding site.
What is the structure of the cell wall?
- Made up of polysaccharides
- Has a middle boundary lamallae to separate adjacent cell walls.
What is a plant cell wall made of?
Cellulose
What is a bacteria / fungi cell wall made of?
Murein
What is the function of the cell wall?
- Provides support to cell.
- Acts as a barrier to pathogens.
- Provides the apoplast pathway for the diffusion of water in plants.
What is the structure of the vacuole in plants?
Simple membrane containing cell sap.
What is the function of the vacuole in plants?
- Support the plant.
- Provides and stores sugars / amino acids / minerals / enzymes etc.
What is the function of plasmids in prokaryotes?
Carries DNA.
What is the function of the flagella in prokaryotes?
Allow some organisms to travel.
What is the function of the capsule in prokaryotes?
Provides mechanical and structural support to prokaryotes.
What are the similarities between eukaryotes & prokaryotes?
- Cell membrane
- Cytoplasm
- Ribosomes
How are prokaryotes different to eukaryotes?
- No organelles
- No nucleus
- circular DNA
- smaller ribosomes
- DNA is not associated with histones
(some have flagella, pilli, plasmids)
What are the principles of optical microscopes?
- Lenses focus light on specimen.
- Reflected light can be seen through the eyepiece.
What are the advantages of an optical microscope?
- Colour image
- Can use lining specimen
- Cheaper
What are the limitations of an optical microscope?
- Needs a long wavelength of light.
- Has low/no resolution.
- Specimen need to be dyed before they are observed.
What are the principle of the transmission electron microscope?
- Beam of electrons is absorbed by a thin specimen.
- Darkest means more electrons absorbed.
- Lighter means less electrons absorbed.
What are the advantages of a TEM?
- Very powerful magnification
- High resolution
What are the limitations of a TEM?
- 2D image.
- Black and white image.
- Electron beam kills specimen.
- Very complex staining process for a thin specimen.
What are the principles of the scanning electron microscope?
- Beam of electrons is focused onto the specimen.
- Electrons are reflected off onto an observable plate. (where the image is produced)
What are the advantages of a SEM?
3D image
What are the limitations of a SEM?
- Needs a vacuum for the specimen.
- Lower resolution than TEM
- Black and white image.
- Very complex staining process for specimen.
How do you prepare a slide for an optical microscope?
- Put a thin specimen onto a slide.
- Add a drop of stain on top.
- Add a coverslip, using a mounted needle at a 45 degree angle. (this prevents air bubbles)
What is the definition of resolution?
The ability to distinguish between two objects.
What is the definition of magnification?
How many times bigger images appear compared to the actual object.
What is the formula that shows the relationship between magnification, image size and actual size?
Magnification = Image size / actual size
How do you calibrate a microscope?
Using the eyepiece graticule and stage graticule.
What does the stage graticule do?
Shown the true length (essentially a ruler)
What does the eyepiece graticule do?
- Has regular divisions, calibrated against the stage graticule at every magnification.
- Stay the same at every magnification.
- You need to find out the length of each division to calibrate to actual lengths of a structure.
What is the process of cell fractionation?
When cells are broken up into their organelles.
What are the conditions necessary for cell fractionation?
COLD, to stop enzyme action
BUFFERED, to keep a constant pH
ISOTONIC: to prevent osmotic changes in organelles
What is the first stage of cell fractionation?
Homogenisation.
Outline homogenisation.
- Cells are broken up in a homogeniser.
- This releases the organelles.
- The homogenate is then filtered to get rid of debris.
What is the second stage of cell fractionation?
Ultracentrifugation
Outline ultracentrifugation.
- Homogenate us spun in a centrifuge at low speeds.
- The heaviest organelle is forced to the bottoms and forms the sediment.
- The sediment is removed, leaving the supernatant.
- The supernatant is re-spun at a higher speed to obtain the next heaviest organelle as the sediment.
- This process continues until all the organelles are separated.
What is the order of sediment after ultracentrifugation?
- Nucleus
- Mitochondria
- Chloroplasts
