cell structure Flashcards
place there units in order from smallest to largest:
kilometre, metre, micrometre, millimetre, nanometre
- nanometre
- micrometre
- millimetre
- metre
- kilometre
match the unit up to their equivalence to metres:
kilometre, metre, millimetre, micrometre, nanometre
km = 1000m
m = 1m
mm = 10^-3
um = 10^-6
nm = 10^-9
what is the minimum distance between 2 points that a light microscope can resolve?
200nm or 0.2 umw
what is the maximum useful magnification of a light microscope?
1500
what is the definition of magnification?
how much bigger the image is than the real specimen
what is the definition of resolution?
the ability to distinguish between two points that are close together, and see them as separate structures
what is the equation for magnification?
magnification = image size/actual size
what is cell fractionation and ultracentrifugation?
a method used to break open cell and separate all of the organelles
before the cells are broken open, they need to be placed in a solution. what 3 things does this solution need to be?
- cold
- isotonic
- buffered
why does the solution that cells are placed in before they are broken open and centrifuged need to be cold?
because this reduces enzyme activity that could lead to the break down of organelles
why does the solution that cells are placed in before they are broken open and centrifuged need to be isotonic?
so that the solution has the same water potential as the cells and does not cause the cells to burst or shrink
why does the solution that cells are placed in before they are broken open and centrifuged need to be buffered?
so that the PH of the solution doesnt fluctuate and change the function of the enzymes or structure of organelles inside the cell
what are the two stages of cell fractionation?
- homogenisation
- ultracentrifugation
how is homogenisation of cells achieved and what is removed in the process?
- cells are broken up in a blender, which releases organelles from the cell
- the homogenate (resultant fluid) is then filtered to remove complete cells and debris
describe the process of ultracentrifugation
- cellular fragments are placed in a machine called a centrifuge
- fragments are spun at a low speed so the heaviest organelles are forced to the bottom, where they form a thin layer of sediment called pellets
- the supernatant (fluid at the top of the tube) is removed
- supernatant placed into another tube and spun again at a faster speed than before, forcing the next heaviest organelle to the bottom
- the process is repeated at faster speeds until all organelles are separated
at what speed of the centrifuge are the following organelles separated?;
nuclei, mitochondria, lysosomes
- nuclei = 1000
- mitochondria = 3500
- lysosomes = 16,500
what are the two types of electron microscope?
- transmission electron microscope (TEM)
- scanning electron microscope (SEM)
what is the highest magnification of a TEM?
500,000
how does a TEM work?
- electrons fired from an electron gun and pass through a section of the specimen
- electrons can behave as very short electromagnetic waves, so give a very high resolution
- the electron beam is focused using electromagnets
- the denser part of the specimen absorbs more electrons, so appears darker
- the image is then produced on a fluorescent or photographic plate
what is the resolution of a TEM?
0.1nm or 0.0001um
give 3 limitations of a TEM?
- living specimens cannot be viewed as specimens must be in a vacuum
- specimens must be extremely thin
- specimens must be killed and chemically fixed which is a complex and time consuming process
- this method can result in artefacts
- can only capture 2d images
- the image is in black and white
what is an artefact?
something that can appear on the final image created by a transmission electron microscope that is not a part of the specimen
how does a SEM work?
- electrons are passed across the surface of the specimen
- the scattered electrons form a image on a screen
- depressions in the specimen appear dark, and extensions appear light
- creates a 3d image
give 2 limitations of a SEM
- resolving power is less than a TEM (0.2nm)
- cant see inside cells
give 2 advantages of a SEM?
- produces 3d images
- high magnification
- specimens dont need to be thin
- preparation technique is less complex so less chance of an artefact
what are the four components of the nucleus?
- nucleolus
- nuclear pore
- chromatin
- nuclear envelope
what is the nucleolus and what is it function?
- part of the nucleus
- site of ribosome synthesis
what is the nuclear pore and what is it function?
- part of the nucleus
- allows the diffusion of large molecules (MRNA) out of the nucleus
what is chromatin?
- part of the nucleus
- diffuse form of chromosomes
what is the nuclear envelope and what is its function?
the outer part of the nucleus with the rough endoplasmic reticulum (REM)
what are the three components of a mitochondria?
- cristae
- matrix
- outer membrane
what are cristae and what are their function?
- extensions of the inner membrane of the mitochondria
- increase surface area for enzyme attachment + other proteins used for respiration
what is the matrix and what is its function?
- semi- rigid material in the mitochondria
- contains proteins, lipids, ribosomes and DNA
what is the function of the outer membrane of a mitochondria?
controls entry and exit of materials
what is the mitochondria?
- site of aerobic respiration
- site of production of ATP from carbohydrates
what are the 7 components of a chloroplast?
- outer membrane
- stroma
- granum
- thylakoid
- thylakoid membrane
- inner membrane
- inter-granal lamella
what are ribosomes?
- tiny granules made from 2 subunits
- 1 small subunit and 1 large subunit
- either float freely in the cytoplasm or are attached to the rough endoplasmic reticulum
what is the function of a ribosome?
site of polypeptide synthesis
what are the 2 sizes of ribosomes and where are they found?
- 70s; found in prokaryotic cells
- 80s; found in eukaryotic cells
what is the rough endoplasmic reticulum and what is its function?
- a membrane that encloses a network of flattened tubes called cisternae
- continuous with the outer nuclear envelope
- has ribosomes attached to it for protein synthesis
- provides a pathway for the transport of materials
what is the smooth endoplasmic reticulum and what is its function?
- a membrane which encloses a network of flattened tubes called cisternae
- no ribosomes attached
- site of lipid and carbohydrate synthesis, store and transport
what is the Golgi apparatus and what are 2 of its functions?
- a stack of flattened sacs surrounded by membranes
- combination of carbohydrates and proteins (glycoproteins)
- processes enzymes
- secretes carbohydrates
- transport, store and modify lipids
what are lysosomes and what are their functions?
- small vesicles (spheres) produced by the golgi apparatus
- they contain hydrolytic enzymes (lysozymes) which digest unwanted materials in the cell
- separated from the rest of the cell by membrane
- digest pathogens, worn out organelles, and the cell when it dies
what is the structure and function of a plant vacuole?
- contains minerals, ions, sugars, amino acids, waste and pigments
- gives cell rigidity and support
- sugars and amino acids can act as temporary food stores
how are prokaryotic cells different to eukaryotic ones?
- smaller
- no nucleus
- no membrane bound organelles
what are the structures in a prokaryotic cell?
- plasmids
- ribosomes
- cytoplasm
- cell-surface membrane
- cell wall
- slime capsule
- flagellum
- genetic material
what is the role of the slime capsule on a prokaryotic cell?
- protects bacterium against other cells
- helps groups of bacteria to stick together
what is the role of the cell wall on a prokaryotic cell?
acts as a physical barrier which excludes certain substances, protects against mechanical damage and osmotic lysis
what is the function of the flagellum?
used for locomotion
what is the function of the plasmids?
posses genes that aid survival in adverse conditions
what are the structural elements of HIV?
- genetic material (RNA)
- attachment protein
- capsid
- lipid envelope
- matrix
- reverse transcriptase
what is reverse transcriptase?
an enzyme which catalyses the production of DNA to RNA
what is an attachment protein?
a protein used by the virus to identify and attach to host cells
give 2 examples of specialised cells?
- sperm
- dendrite
- root hair cell
