3.2.1 | CELL STRUCTURE Flashcards
- add prokaryotes organelles and SEM + TEM
what are the distinguishing feature of eukaryotes
cytoplasm containing membrane-bound organelles and DNA enclosed in nucleus
describe the structure of the phospholipid bilayer
hydrophilic phosphate heads attracted to water pointing outwards and hydrophilic fatty acid tails repelled from water facing inwards
describe the function of the cell-surface membrane
selectively permeable which enables control of substance entering and leaving cell
receptors (glycoproteins/glycolipids) on surface allow cell recognition/signalling
describe the structure of the nucleus
surrounded by a nuclear envelope (double membrane) containing nuclear pores
contains nucleolus
contains linear DNA/chromatins
describe the function of the nucleus
holds/stores genetic information which codes for polypeptides
site of DNA replication
site of transcription, producing mRNA
nucleolus makes ribosomes/rRNA
what is a ribosome made of
ribosomal RNA and protein
describe the function of a ribosome
site of protein synthesis
describe the structure of rough and smooth endoplasmic reticulum
rER and sER are both a network of cisternae (fluid-filled membrane-bound sacs)
rER has ribosomes on surface
describe the function of rough endoplasmic reticulum
ribosomes on surface synthesise proteins
proteins processed/transported inside rER
proteins packed into vesicles for transport to golgi apparatus
describe the function of smooth endoplasmic reticulum
synthesises and processes lipids
describe the structure of golgi apparatus
flattened fluid-filled membrane-bound sacs called cisternae and golgi vesicles
describe the function of golgi apparatus
modifies proteins and lipids
packages proteins/lipids into golgi vesicles
produces lysosomes
describe the function of golgi vesicles
transports proteins/lipids to their required destination
describe the function of lysosomes
digest pathogens using enzymes (lysozymes) and break down waste material
what size are ribosomes in eukaryotes
80S
describe the structure of lysosomes
membrane bound organelle containing hydrolytic enzymes
describe the structure of mitochondria
surrounded by a double membrane with cristae (inner membrane fold)
matrix containing 70S ribosomes and circular DNA
describe the function of mitochondria
site of aerobic respiration to produce ATP for energy release
describe the structure of chloroplasts (in plant and algae)
double membrane enclosing stroma (fluid)
stroma contains thylakoids, starch granules, 70S ribosomes and circular DNA
contain lamella (thylakoid linking grana)
contain grana (stacks of thylakoid)
describe the function of chloroplasts (in plants and algae)
absorb light energy for photosynthesis
what is the cell wall in plants and algae composed of
cellulose
what is the cell wall in fungi composed of
chitin
describe the function of the cell wall in plants, algae and fungi
provides strength to cell to prevent bursting or cell changing shape under pressure
describe the structure of the cell vacuole in plants
tonoplast membrane surrounding cell sap
describe the function of the cell vacuole in plants
maintains turgor pressure in cell, preventing plant from wilting
contains cell sap which stores sugars, amino acids, pigments and any waste chemicals
what is a tissue
group of specialised cells with a similar structure working together to perform a specific function
what is an organ
group of tissues performing specific functions
what is an organ system
group of organs working together to perform specific functions
what size of ribosomes in prokaryotes
70S
what are the distinguishing features of prokaryotes
cytoplasm lacks membrane-bound organelles and DNA not enclosed in a nucleus
what is the cell wall in prokaryotes composed of
murein
explain why viruses are described as acellular
not made of cells, no cell membrane/cytoplasm/organelles
explain why viruses are described as non-living
have no metabolism, cannot independently move/respire/replicate
describe the general structure of a virus particle
nucleic acids surrounded by a capsid
attachment proteins allow attachment to host cells
no cytoplasm, ribosomes, cell wall, cell-surface membrane etc.
some also surrounded by a lipid envelope (HIV)
define resolution
the minimum distance apart two objects can be distinguished as separate objects
define magnification
number of times greater an image is than the size of the real object
give the equation for magnification
magnification = image size / actual size
describe and explain the principles of cell fractionation and ultracentrifugation as used to separate cell components
homogenise tissue/ use a blender
- breaks open cell releasing organelles
place in a cold, isotonic, buffered solution
- cold to reduce enzyme activity so organelles are not damaged
- isotonic to prevent water moving in or out of organelles causing them to burst
- buffered to keep pH constant so enzymes don’t denature
filter to remove large debris
ultracentrifugation: separates organelles in order of density
- centrifuge at a high speed
- remove pellet of heaviest organelle and respin supernatant at a higher speed
- repeat at increasing speeds until desired organelle
why do light microscopes have low resolution
long wavelength of light
why do SEM and TEM have high resolution
short wavelength of electrons
how does a TEM produce an image
electrons pass through specimen
denser parts absorb more and appear darker
how does a SEM produce an image
electrons deflected/bounce off specimen surface
what image does a SEM produce
2D image of cross section
black and white
how does an optical microscope produce an image
light passes though specimen
different structures absorb different amounts and wavelengths
what image does a TEM produce
3D image of surface
black and white
what image does an optical microscope produce
2D image of cross section
coloured (with stain)
what microscope(s) are internal structures of a specimen visible with
TEM
