Topic 2: Cell Biology

function of nucleus

function of nucleus

contains DNA to instruct the cell’s activities

structures of nucleus

nucleolus, chromatin, nuclear pore, and nuclear envelope

function of nucleolus

produces/transcribes rRNA and assembles ribosomes

function of nuclear pore

allow/control the transport of substances in and out the nucleus (eg. RNA)

function of mitochondria

site of aerobic respiration, producing ATP

structures of mitocondria

cristae (folds), matrix (jelly), inner and outer membrane

function of ribosomes

site of protein synthesis (translation)

structures of ribosomes

small and large subunit

difference between prokaryotic and eukaryotic ribosomes

prokaryotic = 70s (smaller)

eukaryotic = 80s (larger)

what are ribosomes made of?

proteins and rRNA

function of smooth endoplasmic reticulum

synthesises and processes lipids

structure of smooth endoplasmic reticulum

membrane enclosed, fluid-filled space

function of rough endoplasmic reticulum

folds and processes proteins

contains ribosomes on surface

structure of rough endoplasmic reticulum

membrane enclosed, fluid-filled space covered in ribosomes

function of Golgi apparatus

processes and packages new lipids and proteins,

makes lysosomes/vesicles

function of Golgi vesicle

stores lipids and proteins made in Golgi apparatus and transports them around the cell

function of lysosomes

contains digestive enzymes (lysozymes/hydrolytic) that break down invading cells or broken organelles

function of cytoplasm

where the cell’s chemical reactions/functions take place

function of cell-surface membrane

regulate movement of substances in and out the cell

function of cell wall

supports cell and prevents it from changing shape

what are cell walls made of in:

plants

fungi

bacteria

cellulose

chitin

murein

function of chloroplasts

site of photosynthesis

structures of chloroplasts

granum, thylakoids, lamella, stroma, and double membrane

functions of vacuole

maintain pressure

keeps rigidity

stops wilting

isolate unwanted chemicals

membrane of vacuole

tonoplast

magnification definition

how much bigger the image is than the specimen

magnification equation

magnification = image size / actual size

resolution definition

how detailed the image is,

how well you can distinguish between two separate points close together

advantage of light microscope

cheap, small, and portable,

about x1500 magnification, enough for eukaryotic cells,

on living cells

limitations of light microscope

samples must be thin to allow light through,

no 3D images,

maximum magnification is lower than most organelles

eyepiece lens equation

magnification = eyepiece lens x objective lens

principle of transmission electron microscope

electromagnets focus beam of electrons through the specimen,

darker the image, more electrons are absorbed, denser the area,

vacuum in the microscope, no air

advantage of transmission electron microscope

high resolution,

high magnification

limitations of transmission electron microscope

only on thin, non-living specimen,

very expensive

principle of scanning electron microscope

scan beam of electrons across the surface,

knocks electrons of specimen and these are ‘gathered’ to form image,

vacuum in the microscope, no air

advantage of scanning electron microscope

thick specimen,

3D images,

high resolution (lower than TEM)

limitations of scanning electron microscope

lower resolution than TEM,

only on non-living specimen,

very expensive

temporary/wet mount

1. pipette a small drop of water onto the slide.

2. use tweezers to add thin slice of specimen.

3. add a drop of stain, to highlight the cell.

4. place coverslip on slide: upright, tilt and lower it (no air bubbles).

artefacts

things you can see down the microscope that are not part of the cell or specimen: dust, bubbles of air, and fingerprints.

principle of cell fractionation

1. homogenise cells/tissue in blender.

2. filter through gauze to remove cell debris.

3. under cold, isotonic, and pH buffer conditions.

4. centrifuge the mixture, initially at lower speeds and removing the supernatant to spin at higher speeds.

why is cell fractionation done under cold temperatures?

to reduce enzyme activity, so that the hydrolytic enzymes/lysozymes do not digest the cell

why is cell fractionation done under isotonic conditions?

so the cell is not osmotically damaged/prevent it bursting from osmotic pressure

why is cell fractionation done under pH buffered conditions?

to maintain pH, so that the proteins do not denature/change shape

principle of ultracentrifugation

the cell solution is span at a lower speed and the most dense organelles are pushed to the bottom of the homogenate, forming a pellet

The rest stays above the pellet as a supernatant

supernatant is span at higher speeds so the second most dense organelle reaches the bottom.

Process is repeated till desired organelle is isolated

importance of mitosis

growth of new identical cells

repair of damaged tissue

reproduction asexually

interphase

cell growth and organelles are replicated so the cell is ready to divide

DNA replication

prophase

chromosomes condensing,

bundles of proteins called centrioles migrate to opposite poles, forming spindle fibres,

nuclear envelope breaks down

metaphase

chromosomes align down the equator of the cell,

centromeres attach to spindle fibres

anaphase

spindle fibres contract,

centromeres divide,

sister chromatids pulled to opposite poles

telophase

chromatids reach opposite poles,

uncoil back into chromosomes,

nuclear envelope forms around them - 2 nuclei

cytokinesis: cytoplasm divides

mitotic index equation

mitotic index = number of cells with visible chromosomes (undergoing mitosis) / total number of cells in sample

mitotic index practical: why add hydrochloric acid

to break up the tissue into individual cells

mitotic index practical: why apply pressure to/press down firmly on the slide

pressing will separate the cells into individual cells in a single layer

mitotic index practical: why should the coverslip not slide sideways over specimen

to avoid damaging the chromosomes

mitotic index practical: why should you avoid air bubbles under the coverslip

so the image is not distorted

mitotic index practical: what is the tissue called where mitosis occurs in shoot and root tips

meristem

(it is totipotent and retains ability to differentiate)

mitotic index practical: what are the knobs called that allow you to focus the microscope

coarse adjustment knobs (larger adjustments)

fine adjustment knobs (careful adjustments)

components of cell-surface membrane

phospholipid bilayer,

channel and carrier proteins,

cholesterol,

glycoprotein

fluid-mosaic model

fluid = idea of molecules moving

mosaic = idea of made up of both proteins and phospholipids

function of cholesterol

membrane stability,

packs phospholipids closely together,

restricts movement, less fluid,

helps maintain shape of cells,

lipid, so in all membrane

permeability of membrane <0 degrees Celsius

very high:

no energy = low movement,

proteins denature,

ice crystals puncture membrane

permeability of membrane 0-45 degrees Celsius

low-medium:

phospholipids can move, not too tight,

more movement = more permeable

permeability of membrane >45 degrees Celsius

very high:

phospholipid bilayer melts and more permeable

water expands = increase pressure

proteins denature

simple diffusion

diffusion of small, non-polar molecules down a concentration gradient

facilitated diffusion

facilitated diffusion down a concentration gradient via carrier and channel proteins

osmosis

osmosis/diffusion of water down a water potential gradient

active transport

movement against the concentration gradient via protein carrier using ATP

co-transport

co-transport of 2 different substances using a carrier protein

co-transport of glucose and sodium ions

1. sodium ions actively transported out of the ileum epithelial cells, creating a concentration gradient

2. sodium ions then diffuse back into the cells, via sodium-glucose co-transport proteins

3. co-transporter carries sodium with glucose into the cell, concentration of glucose increases in the cell

4. glucose diffuses out the cell, into the bloodstream, through a protein channel by facilitated diffusion

water potential practical: where is the isotonic point on the percentage change against concentration graph

where the line of best fit crosses the x-axis

water potential practical: why do you dry the potato chips

to remove excess water before weighing them

water potential practical: why calculate percentage change in mass rather than change in mass

to able to compare potato chips as they did not all have the same initial mass

membrane permeability practical: colorimeter

measures how much light is transmitted/passes through which allows you to quantitively compare amount of pigment released

ie. more pigment released = less light transmitted

membrane permeability practical: what should be used to set zero on a colorimeter

distilled water

membrane permeability practical: effect of ethanol concentration on permeability

as ethanol concentration increases, the permeability of the membrane increases so more pigment is released

because ethanol/alcohol dissolves the lipids causing more gaps and fluidity of the cell-surface membrane

tumour

uncontrolled cell division due to mutation in the gene

structure of bacteria

loop of DNA, DNA plasmids, cell wall, cell-surface membrane, capsule, flagellum, and 70s ribosomes

function of flagellum of prokaryotic cell

enables movement of prokaryotic cells

function of capsule of prokaryotic cell

protect bacteria from immune system,

prevents from drying out

binary fission

1. replicate all its circular DNA and plasmids

2. cell gets bigger and DNA moves to opposite poles

3. cell wall begins to form

4. cytokinesis to form two daughter cells (non-identical)

structures of virus

genetic information (RNA/DNA), capsid, and attachment protein

antigen

protein/glycolipid that identifies a cell and triggers an immune response

phagocytosis

1. receptor on membrane of phagocyte binds with antigen

2. engulf the pathogen, forming a phagocytic vacuole

3. phagocytic vacuole fuses with lysosome (phagosome) releasing lysozymes

4. enzymes digest the pathogen and digested parts are presented on the cell-surface membrane: antigen-presenting cell

5. exocytosis, removing broken down parts

role of helper T cells

to stimulate cytotoxic T cells, B cells, and phagocytes

clonal selection

B-lymphocytes with complementary receptors to foreign antigen are stimulated to divide by mitosis

producing a large number of B-lymphocytes to become plasma or memory cells

antibody definition

protein that is specific to an antigen

structure of antibody

Y-shaped structure which consist of 4 polypeptide chains:

2 heavy and 2 light chain

variable region that change to be complementary to antigen

two binding sites

agglutination

two binding sites bind to two pathogens, grouping together

(antibodies may neutralise or act as a marker)

primary response

slow

antigen enters 1st time

B cells must be produced for enough antibodies

long-lasting memory B cells

secondary response

fast

antigen enters 2nd time

immediate clonal selection

memory B cells activated

effect of antigenic variability

memory B cells cannot be activated by the antigen because its structure/shape changes every time

primary response is triggered each time

symptoms are displayed each time

principle of vaccines

introduce dead or inactivated pathogen into body to produce primary immune response

creating memory B cells

how vaccine protects?

1. vaccine contains antigen

2. displayed on antigen-presenting cells

3. specific helper T cells stimulates specific B cells

4. B cells divide (mitosis) to give plasma cell

5. B cells/plasma cells produce antibody

ethical issues of vaccines

production and testing may be done against animals

risk of vaccine needs to be balanced against benefits

tested on humans (to determine toxicity)

expensive

compulsory? / opt-in/opt-out schemes?

herd immunity

sufficiently large proportion of the population are immune/vaccinated so it is difficult for the pathogen to spread

natural active immunity

being exposed to the antigen/disease

artificial active immunity

through vaccination which stimulate immune response

natural passive immunity

crossing mother’s antibodies through placenta or breast milk

artificial passive immunity

antibodies are injected into a body

passive vs active immunity

active = protection is slower and requires exposure to antigen

memory cells are produced

passive = protection is immediate and does not require exposure to antigen

memory cells are not produced, antibodies broken down