2.1.1 Cells Flashcards
Structure and function of nucleus
- nucleolus - densest part of the cell (site of ribosome production)
contains chromatin which makes up chromosomes ( wound around histones )
surrounded by nuclear envelope (double membrane) which has nuclear pores to let mRNA and ribosomes through
Structure of mitochondria
surrounded by double membrane
inner membrane folds to form cristae
cristae forms matrix which contains enzymes needed for aerobic respiration
small mitochondrial DNA and ribosomes found in matrix
Structure of chloroplasts
surrounded by double membrane
thylakoids (membrane bound compartments containing chlorophyll) stack to form grana
grana are joined by lamellae (thin and flat thylakoid membrane)
Structure of ribosomes
found either freely in the cytoplasm or on the rough ER
80s in eukaryotic
70s in prokaryotic, mitochondria and chloroplasts
Function of ribosomes
site of translation
Structure of rough endoplasmic reticulum
formed from folds of membrane continuous with the nuclear envelope
surface covered in ribosomes
Function of rough endoplasmic reticulum
processes proteins made by the ribosomes by folding primary structures into secondary and tertiary structures
Function of smooth endoplasmic reticulum
synthesises, processes and stores lipids carbohydrates and steroids
Structure of golgi apparatus
flattened sacs of fluid-filled membrane
has secretory vesicles to transport molecules
vesicles enter the cis face and leave via the trans face
Function of golgi apparatus
modifies proteins and lipids
packages them into golgi vesicles
vesicles transport proteins out of the cell (exocytosis), or to membrane bound organelles
Structure and function of vesicle
membrane-bound sac
used for transport and storage
Structure and function of lysosome
specialist vesicle which contains hydrolytic enzymes (break biological molecules down)
used by immune system in phagocytosis
Structure of centriole
hollow fibres made of microtubules
two centrioles at right angles to each other form a centrosome
Function of centrioles
form centrosomes which organise spindle fibres in cell division
Structure of microtubules
made of alpha and beta tubulin combined to form protofilaments
- 13 protofilaments in a cylinder make a microtubule
What is a cytoskeleton made of
- microfilaments
- microtubules
- intermediate fibres
Structure and function of microfilaments
made of actin
responsible for cell movement and contraction during cytokinesis
Function of microtubules
acts as tracks for the movement of organelles around the cell
make up spindle fibres used for cell division
Function of intermediate fibres
provide mechanical strength and help maintain integrity
What is the cell wall made of
peptidoglycan in prokaryotes
cellulose in plants
Organelles that are always present in prokaryotes
- cell wall
- cell membrane
- cytoplasm
- circular strand of DNA
- 70s ribosomes
Organelles that are sometimes present in prokayotes
- flagellum
- slime capsule
- infolding of surface membrane
- plasmids
- pili
Structure and function of flagellum
hair like structure with basal hook that attaches to cell membrane
rotates - mechanical motor
Function of slime capsule
protects bacteria from drying out
protects from attack from immune system cells
Function of plasmids
small loops of DNA that can be passed between bacterial cells
often contain genes for antibiotic resistance
Describe the role of the nucleus in protein production
- ribosomes are produced in the nucleolus
- DNA is transcribed into mRNA which leaves the nucleus via the nuclear pore to a ribosome on the rough ER
Describe the role of the rough ER in protein production
polypeptides move into the rough ER cisternae
primary structures are folded into secondary and tertiary structures
proteins are packaged into vesicles
Describe the role of the golgi in production of proteins
vesicle fuses with cis face golgi and releases protein into golgi
protein is modified and packaged into secretory vesicle
vesicle leaves the trans face golgi and fuses to the cell membrane to release the protein through exocytosis
What is the membrane surrounding the vacuole called
tonoplast
What is resolution
the smallest distance that two points can be distinguished from each other
Benefits of light microscopes
- cheap
- easy to use
- can view living organisms and cells
Drawbacks of light microscopes
- maximum resolution - 0.2 micrometres
- maximum useful magnification - x1500
- therefore cannot be used to observe smaller organelles (rough ER etc)
- 2D images only
How does a transmission electron microscope work
an electron beam is transmitted through the specimen
denser parts of the specimen absorb more electrons so appear darker
- specimen are dead and dipped in heavy metals (lead) to scatter electrons then embedded in wax
Benefits of using a transmission electron microscope
- higher resolution - 0.5 nm
- higher magnification - over x500,000
Drawbacks of using a transmission electron microscope
- black and white 2D images
- dead specimen due to vaccum
- lengthy treatment to produce very thin specimen
How do scanning electron microscopes work
a beam of electrons hits the specimen and is scattered
electrons are detected, forming an image
- SEM’s can produce 3D images of the surfaces of specimens
Benefits of scanning electron microscopes
- images of external, 3D structure can be observed
- maximum resolution of 3-10nm
- maximum magnification of x 500,000
Drawbacks of scanning electron microscopes
- maximum resolution lower than TEM
- black and white images - can colour digitally
- dead specimen due to vaccum
Benefits of staining specimen
increases the contrast - so different organelles can be visible e.g. nuclei
- so different biological molecules are visible e.g. starch grains
What is the use of methylene blue
stains DNA blue
What is the use of acetic orcein
stains DNA red
What is the use of iodine
stains starch blue/black
stains cell walls brown/yellow
What are the different types of sample preparation
- dry mount
- wet mount (specimen in liquid such as water or an immersion oil)
- squash slides
- smear slides
Describe how to measure the size of X using a light microscope
use eyepiece graticule
calibrate the graticule using a stage micrometre
measure the length of X in eyepiece units
use calibrated epu to calculate the actual length of X
