2.1 Cell structure Flashcards
function of cell surface membrane
- regulates the movement of substances into and out of the cell
- has receptor molecules which allow response to chemicals
function of the nucleus
- controls cells activities by controlling the transcription of DNA
- DNA contains instructions to make proteins
- pores allow substances to move between nucleus and cytoplasm
- nucleolus makes ribsomes
describe the nucleus
- nucleus envelope > double membrane
contains chromosomes and nucleolus
description of mitochondria
- oval shaped
- double membrane > inner is folded to form cristae
- inside is the matrix > enzymes involved in respiration
function of mitochondria
- site of aerobic respiration > produces ATP
description of chloroplast
- double membrane
- thylakoid membrane
function of chloroplasts
site where photosynthesis takes place
description of golgi apparatus
group of fluid filled membrane bound flattened sacs
contain vesicles
function of golgi apparatus
processes and packages new lipids and proteins
- makes lysosomes
description of golgi vesicle
small fluid filled sac in cytoplasm
function of golgi vesicle
stored lipids and proteins made by gfi apparatus and transports them out of the cell
function of a lysosome
contains digestive enzymes called lysozymes which can be used to digest invading cells or break down worn out components of the cell
function of a ribosomes
site where proteins are made
what ribosomes are in eukaryotic cells
80s
what are ribosomes made up of
proteins and RNA
description of rough endoplasmic reticulum
system of membranes enclosing a fluid filled space
surface covered with ribosomes
function of rough endoplasmic reticulum
folds and processes proteins that have been made at ribosomes
function of smooth endoplasmic reticulum
synthesises and processes lipids
function of cell wall
supports cells and prevents them from changing shape
what is a cell wall made from in fungi
chitin
function of a cell vacuole
helps maintain pressure inside the cell and keeps the cell rigid
how are epithelial cells specialised
- walls of small intestine have villi > increase surface area
- epithelial cells on surface of villi have folds called microvilli > increase surface area
- lots of mitochondria
how are red blood cells specialised
- biconcave so increases surface area to allow more o2 absorption
- no nucleus > more haemoglobin can be stored
how are sperm cells specialised
- contain lots of mitochondria
cell organisation
cell > tissue > organs > organ system
how are prokaryotic cells different from eukaryotic
- no membrane bound organelles
- smaller ribosomes (70s in prokaryotic)
- no nucleus (circular DNA that is free in cytoplasm, not associated with proteins)
- cell wall with murein
- some contain plasmids, capsule and flagella
how do prokaryotic cells replicate
binary fission
process of binary fission
1 - circular DNA and plasmids replicate
2- cells gets bigger, DNA loops move to opposite ends of the cell
3 - cytoplasm begins to divide
4 - two daughter cells are produced, each with one copy of the circular DNA
why are viruses acellular
- non living
- nucleic acids surrounded by a protein
what are the cells viruses reproduce inside of called
host cells
structure of a virus
- no cell surface membrane, cytoplasm or ribosomes
- contain a protein coat (capsid) with attachment proteins sticking out from it which allow the virus to cling onto a suitable host cell
how do viruses replicate
inject their DNA or RNA into a hose cell which then uses its own machinery to replicate the virus particles
what do attachment proteins bind to
complementary receptor proteins on the cell surface membrane on host cells
what is a eukaryotic cell
cell containing a nucleus and other membrane bound organelles
what is a prokaryotic cell
cell that doesn’t contain membrane bound nucleus or any membrane bound organelles
what is resolution
the ability to distinguish between objects that are close together
what is magnification
how many times bigger the image is than the specimen
calculation for magnification
magnification = image / actual
light microscope
- use a pair of convex glass lenses that can resolve images up to 0.2um apart
- this is because the wavelength of light is used which restricts the resolution a light microscope can resolve to
electron microscope
- use beam of electrons to form an image
- in a vacuum so particles in air don’t deflect beam of electrons
- more detailed images higher resolution
two types of electron microscopes
transmission electron microscope
scanning electron microscope
which microscope forms a 3d image
SEM
how does a transmission electron microscope work
beam of electrons pass through a thin section of specimen
- areas that absorb electrons appear darker on the image produced
how does a scanning electron microscope work
beam of electrons is passed across a surface and scattered
- pattern of scattering builds up a 3D image depending on the contours of the specimen
limitations of SEM and TEM
- whole system must be in a vacuum so loving specimens can’t be observed
- complex staining process is required > artefacts could be introduced
- specimens have to be thin
- SEM has lower resolution than TEM
limitation of light microscope
- lower resolution than electron
how to prepare a sample to look at in a microscope
- pipette a small drop of water onto a slide
- place a thin section of specimen on top of water drop
- add a drop of stain
- add cover slip ( at an angle to prevent air bubbles)
what stain is used in plant cells to see starch grains
iodine in potassium iodide
what are artefacts
anything you can see down the microscope that aren’t part of the cell or specimen you’re looking at
- common in electron micrographs
what is cell fractionation
separating organelles within the cell
steps to cell fractionation
homogenisation
filtration
ultracentrifugation
process of homogenisation
- breaking up the cells to break up the plasma membrane and release organelles into solution
conditions during homogenisation
- solution must be kept cold (reduce enzyme activity)
- isotonic (same concentration of chemicals as the cells being broken down to prevent damage to organelles
- buffer should be aided to maintain pH
process of filtration
- homogenised cell solution is filtered through a gauze to separate large cells debris from organelles
process of ultracentrifugation
- cell fragments poured into a tube
- tube is placed in a centrifuge and spun at low speed
- heaviest organelles are flung to the bottom of the tube and form the pellet (thick sediment)
- rest of organelles stay in the supernatent
- supernatent purer into another tube and spun at higher speed > next heaviest organelle forms pellet
- processes repeated for each organelle
order of seperation in cell fractionation
- nuclei
- chloroplasts
- mitochondria
- lysosome
- endoplasmic reticulum
- ribosome
