Cells (2)

eukaryotic cells

CSM

structure = made of lipids and proteins, found on surface of animal cells

function = regulates the movement of substances in & out of cell, also contains receptor molecules to respond to hormones

nucleus

structure = large organelle, surrounded by nuclear envelope (contains many pores), contains chromosomes and a nucleolus

controls cells activities via transcription of DNA, pores allow substance movement between nucleus & the cytoplasm, nucleolus makes ribosomes

mitochondrion

structure = oval shaped with double membrane, inner one is folded to form cristae, includes matrix containing enzymes in respiration

function = site of aerobic respiration where ATP is produced, found in large no. in cells that are active & require energy

chloroplast

structure = flattened structure in plant/fungal cells, double membrane, also has thylakoid membranes - stack up to form grana (linked by lamellae)

where photosynthesis occurs in grand and stroma

golgi apparatus

structure = fluid filled membrane bound flattened sacs, vesicles are often seen at the edge of the sacs

function = processes & packages new lipids and proteins, also makes lysosomes

golgi vesicle

structure = small fluid-filled sac in the cytoplasm, surrounded by membrane and produced by Golgi apparatus

function = stores lipids & proteins made, transports out of cell

lysosome

structure = round organelle surrounded by membrane, no clear internal structure

function = contains digestive enzymes called lysozymes, digest invading cells or to break down worn out components of the cell

ribosome

structure = small organelle, floats free in cytoplasm or attached to RER, made of proteins/RNA, not surrounded by membrane

function = site where proteins are made

RER

structure = system of membranes enclosing fluid-filled space , surface covered in ribosomes

function = folds & processes proteins that have been made at the ribosomes

SER

structure = same as SER but with no ribosomes

function = synthesises & processes lipids

cell wall

structure = rigid structure surrounds cells in plants, algae & fungi. plants & algae = cellulose. fungi = chitin

function = supports cells and stops them changing shape

cell vacuole

structure = membrane-bound organelle found in cytoplasm of plant, contains cell sap surrounding membrane is the tonoplast

function = helps to maintain pressure inside cell rigid, stops plant wilting, also involved in isolation of unwanted chemicals in cell

specialised cells

cells become specialised to carry out specific functions

organised into tissues, organs & organ systems

epithelial cells in small intestine, specialised to absorb food efficiently

walls of small intestine contain villi -> increase S.A for absorption

contain folds called microvilli that further increase S.A

lots of mitochondria to provide energy for absorption

prokaryotic cells

cytoplasm = no membrane-bound organelles, ribosomes are smaller than eukaryotic

flagellum = long hair-like structure, rotates to make cell move, not all cells have them, some have >1

no nucleus = DNA is circular and floats free in cytoplasm, not attached to histones

plasmids = small loops of DNA, contain genes for things like antibiotic resistance, not always present

plasma membrane = made of lipids and proteins, controls movement of substances in/out of cell

cell wall = supports cell, stops it from changing shape, made of murein (glycoprotein)

slime capsule = protects bacteria from attacks by cells in immune system

viruses

acellular

viruses are nucleic acids surrounded by proteins - they are not alive

smaller than bacteria

no plasma membrane, no cytoplasm, no ribosomes

invade and reproduce inside the cells of other organisms

have attachement proteins

binary fission

cell replicates before physically splitting into 2 daughter cells

circular DNA & plasmids replicate - DNA only replicates once, plasmids can replicate many times

cell gets bigger, DNA loops move to opposite poles of cell

cytoplasm starts to divide and new cell wall forms

cytoplasm divides and 2 new daughter cells produced

use attachment proteins to bind to complementary receptor proteins on surface of host cells

attachment proteins are unique and require different receptor proteins on host cells - some viruses can only infect 1 type of cells as a result

not alive so dont undergo cell division, instead they inject DNA/RNA into host cell and cell replicates viral particles

analysis of cell components

microscopy

magnification = size of image / size of actual object

how much bigger the image is than the specimen you are observing

resolution = how well a microscope can distinguish between 2 points that are close together

optical microscopes

use light to form an image

max resolution of 0.2 micrometres

max useful magnification is x1500

electron microscopes

use electrons to form an image

higher resolution than optical microscopes

max useful magnification is x1,500,000

max resolution = 0.0002 micrometres

transmission electron microscopes

use electromagnets to focus beam of electrons through specimen

denser parts of specimen absorb more electrons and appear darker

give high resolution images so internal structure of organelles can be seen

can only be used on very thin specimens and performed in a vacuum so specimen must be dead

scanning electron microscope

scan a beam of electrons across specimen, knocks off electrons from specimen and collects them in a cathode ray tube to form an image

images show surface of specimen and can be 3D

can be used on thick specimens

give lower res images than TEMs

cell fractionation

homogenisation

place cells in a homogeniser, breaks up plasma membrane and release organelles into a solution

solution must be ice cold = reduce activity of enzymes

solution must be isotonic = same conc. as cells being broken down, to prevent damage to organelles via osmosis

buffer solution must be added to maintain pH

filtration

homogenised cell solution filtered through gauze to separate any cell debris

ultracentrifugation

cell fragments poured into tube & put into centrifuge, spun at low speed. heaviest organelles (nuclei) fall to bottom and form a pellet, organelles suspended in fluid above pellet (supernatant)

supernatant filtered off and put into separate tube, spun in centrifuge at higher speed, heaviest organelle (mitochondria) form pellet again

process repeated at higher speeds until all organelles are spirited out

cell division

cell cycle

consists of period of cell growth and DNA replication called interphase, then mitosis occurs

interphase = G1, S, G2

mitosis

prophase = chromosomes condense, centrioles start to form spindle fibre, nuclear envelope breaks down

G1 = cell grows, new organelles & proteins are made

S = cell replicates DNA, ready to divide via mitosis

G2 = cell keeps growing & proteins needed for division are made

metaphase = chromosomes line up along middle of cell, become attached to spindle by their centromere

anaphase = centromeres divide, separating each pair of sister chromatids. spindles contract, chromatids pulled to opposite poles

telophase = chromatids reach opposite poles, uncoil into chromosomes again, nuclear envelope starts to reform, cytokinesis finishes and 2 genetically identical daughter cells are produced.

cancer

mitotic index = number of cells with visible chromosomes / total no. of cells observed

a mutation in a genes that controls cell division means the cells can grow out of control & keep dividing -> tumour

cancer = a tumour that invades surrounding tissues

cancer treatments

designed to control the rate of cell division in tumour cells by disrupting the cell cycle

dont distinguish normal cells from cancer cells so healthy cells die as a result also

G1 (cell growth & protein production) = chemotherapy prevents synthesis of enzymes needed for DNA replication. cell cannot enter the S phase and is forced to kill itself (apoptosis)

S phase (DNA replication) = radiation & some drugs damage DNA, at several points of cell cycle the cell is checked for damage, if too severe the cell will kill itself - preventing further tumour growth

cell membranes

cell surface membranes

organelle membranes

compartmentalise the cell and acts as barrier between organelle and cytoplasm. partially permeable & determine what enters or leaves the organelle

barrier between cell and its environment, controlling which substances enter/leave cell, partially permeable. substances can move across via diffusion, active transport or osmosis

fluid mosaic model

phospholipid molecules form a continuous bilayer

fluid as phospholipids are constantly moving

cholesterol molecules give the bilayer rigidity

proteins scattered throughout bilayer "like a mosaic" including channel proteins & carrier proteins & receptor proteins

some can move sideways and others are fixed

glycoproteins & glycolipids

restrict movement of phospholipids

head is hydrophilic (attracts water)

tail is hydrophobic (repels water)

center of bilayer is hydrophobic and membrane doesn't allow water soluble substances through it

temperature & membrane permeability

below 0 = phospholipids have no energy, cannot move, rigid membrane. channel/carrier proteins deform (inc. permeability) ice crystals also from that piece membrane (inc. permeability)

between 0-45 = phospholipids are fluid, membrane partially permeable. as temp inc. phospholipids move more as they have more energy (inc. permeabililty)

above 45 = phospholipid bilayer starts to melt (inc. permeability) water in cell expands, puts pressure on membrane. channel/carrier proteins deform cannot control entry & exit (inc. permeability)

diffusion

net movement of particles from an area of higher conc to an area of lower conc

molecules diffuse both ways but net movement is to the lower conc -> until particles evenly distributed

concentration gradient = path from an area of higher conc to an area of lower conc - particles move down conc gradient

simple diffusion = when molecules diffuse directly through a cell membrane

facilitated diffusion

larger molecules = diffuse very slowly through phospholipid bilayer

charged particles = diffuse slowly as they're water soluble & centre of bilayer is hydrophobic

uses carrier proteins & channel proteins to carry molecules across the CSM

passive process

carrier proteins

move large particles across membranes

different proteins facilitate movement of different particles

large molecule attaches to a carrier protein in membrane

protein changes shape

molecules is released on opposite side of membrane

channel proteins

form pores in membrane for charged particles to diffuse through

different channel proteins facilitate movement of different particles

factors affecting diffusion

conc. gradient = higher it is, the faster the rate of diffusion -> slows down over time

thickness of exchange surface = thinner surface, the shorter the diffusion distance -> faster rate

surface area = larger surface area, the faster the rate

factors affecting diffusion

conc. gradient = higher gradient, faster rate

no. of carrier/channel proteins = the greater the number of proteins, the faster the rate of diffusion

osmosis

diffusion of water molecules across a partially permeable membrane from an area of higher water potential to an area of lower water potential

water potential = likelihood of water molecules to diffuse out of or into a solution

pure water = highest water potential

isotonic = 2 solutions with the same water potential

factors affecting rate

water potential gradient = higher water potential, the faster the rate

thickness of exchange surface = the thinner the surface, the faster the rate

surface area = larger surface area, faster rate

active transport

active process, requires energy

uses energy to move molecules across membranes, against a conc gradient

differences between active transport & facilitated diffusion

active transport moves solutes from low -> high conc.

facilitated diffusion moves solutes from high -> low conc

active transport requires energy, facilitated diffusion does not

co-transporters

type of carrier proteins

bind 2 molecules at once

the conc gradient of 1 molecule is used to move the other molecules against it's own conc gradient

factors affecting active transport

speed of individual carrier proteins = faster they work, faster rate

no. of carrier proteins = the more proteins, the faster rate

rate of respiration in cell & ATP availability = inhibited respiration, no active transport

co-transport in the ileum

glucose absorbed into bloodstream in small intestine

in the ileum, conc. of glucose too low for it to diffuse into blood, so glucose absorbed into lumen of ileum via active transport

Na+ actively transported in/out of epithelial cells into blood via NaK pump -> creates conc. gradient

causes Na+ to diffuse lumen -> epithelial cell down conc. gradient via Na-glucose co-transporter protein

co-transporter carries glucose into cell with Na, conc of glucose in cell increases

glucose diffuses out of cell into blood, down conc. gradient via protein channel (facilitated diffusion)

the immune system

antigens = molecules that czan generate an immune response when detected by the body

4 main stages in immune response

found on surface of cells & used by body to identify pathogens, abnormal body cells & toxins

phagocyte recognises foreign antigen on pathogen, cytoplasm of phagocyte engulfs pathogen, pathogen in phagosome, lysosomes release lysozyme that break pathogen, phagocyte presents the antigens on its own surface

phagocytosis

T-cell = has receptor proteins on surface that bind to complementary antigens presented to it by phagocytes. Th cells = activate phagocytes & B-cells Tc cells = kill abnormal/foreign cells

B-cells = covered in antibodies & divide into plasma cells when activated

antibodies bind to antigens to form antibody-antigen complexes

plasma cells are identical to B-cells and secrete antibodies

antibodies are proteins

specificity depends on its variable regions -> form antigen binding sites

each variable region has a unique tertiary structure

all antibodies have the same control region

cellular immune response = T-cells and other immune system cells they interact with

humoral immune response = B-cells, clonal selection & production of monoclonal antibodies

primary immune response = when an antigen enters the body for the first time, slow as there aren't many B-cells, as they are produced the person suffers symptoms, memory cells are produced & remain in body for long time -> person is immune

secondary immune response = if the same pathogen enters body again, response is quicker & stronger, clonal selection happens faster, memory B-cells activated & divide into correct T-cells -> pathogen removed before symptoms even occur

immunity & vaccines

active immunity = when immune system produces it's own antibodies after being stimulated by antigen, natural -> after catching disease, artificial -> after being given a vaccination

passive immunity = immunity after being given antibodies from different organism, immune system doesn't produce any on its own, natural -> when a baby becomes immune via mothers placenta/breastmilk, artificial -> immunity after being injected with antibodies from someone else

differences between active and passive immunity

active = requires exposure, takes a while for protection to develop, memory cells made, long-term protection

passive = doesnt require exposure, immediate protection, no memory cells made, short-term protection

vaccines

contain antigens that cause body to produce memory cells against a pathogen

herd immunity = protection of enough individuals to reduce the occurrence of disease

can be injected or given orally

oral = less effective as molecules may be too larger to be absorbed into blood

antigenic variation

different antigens form due to changes in genes of a pathogen

memory cells from first infection will not recognise different antigen

antibodies in medicine

monoclonal antibodies are antibodies produced from a single group of genetically identical B-cells

cancer cells

cancer cells have antigens - tumour markers (not found on normal body cells)

monoclonal antibodies can be made to bind to tumour markers

anti-cancer drugs can be attached to monoclonal antibodies

drug will accumulate in body where there are cancer cells

side effects of anti-cancer drugs less than others as they accumulate at specific cells

pregnancy testing

detect hCG in urine of pregnant women

application area contains antibodies for hCG bound to coloured bead

when urine applied, hCG will bind to antibody on beads forming antigen-antibody complex

urine moves up test stick, carries beads with it

test strip contains immobilised antibodies to hCG

if hCG is present test strip turns blue as immobilised antibody binds to any hCG, if no hCG present the beads pass through test without binding so no blue is present

ELISA testing

direct ELISA = uses single antibody complementary to antigen being tested for

indirect ELISA = uses 2 different antibodies complementary to antigen being tested for

ELISA as a HIV test

HIV antigen bound to bottom of well in a well plate

sample of blood plasma added to well, any HIV antibodies will bind to HIV antigen stuck to bottom of well - then washed to remove unbound antibodies

a secondary antibody with a specific enzyme attached is added to the well, can bind to HIV antibody & well is washed out to remove any unbound secondary antibody

a solution is added to the well containing a substrate, can react with enzyme attached to 2nd antibody and form a coloured solution. if solution changes colour, patient has HIV antibodies and is positive for HIV

interpreting vaccine & antibody data

MMR vaccine

in 1998 a study was published linking MMR vaccine & autism

had a very small sample size - 12 children

potential for bias - one of the scientist was working to gain evidence for a lawsuit against the MMR vaccine

further studies carried out in Japan with larger sample sizes to sort conflicting evidence

describing data - look for patterns, trends, anomalies - quote specific data & manipulate it

draw conclusions - look if there is an overall link

evaluate methodology - smaller sample size = result more likely to be due to chance

Herceptin - monoclonal antibodies

describe data - almost 2x as many women in control group developed breast cancer again or died compared to group taking Herceptin

draw conclusions - after a 1 year treatment, after chemo, disease free survival rate increases

ethical issues with vaccines

animal testing or contain animal-based substances (unable to be used by vegetarians/vegans)

testing on humans - volunteers may put themselves at unnecessary risk as a last ditch effort

some dont take vaccine due to fear of side effects but are still protected by herd immunity - causes social tension

if there was an epidemic, it is difficult to decide who needs the vaccine first

ethical issues with monoclonal antibodies

often involve animal rights issues, animals used to produce monoclonal antibodies

HIV & viruses

HIV

a virus that affects the immune system & leads to AIDS

AIDS = condition where immune system deteriorates & eventually fails

HIV infects/kills Th cells (act as host cells) without them, no signals can be sent to activate phagocytes, Tc cells & B cells

structure of HIV

spherical

core = contains genetic material (RNA) & some proteins (reverse transcriptase) needed for virus replication

capsid = outer coating of protein

envelope = extra outer layer made of membrane stolen from CSM of previous host cell

attachment protein = stick out from envelope, help HIV attach to host Th cell

replication of HIV

attachment protein attaches to receptor molecule on cell membrane of host Th cell

capsid released into cell, uncoats & releases RNA into cells cytoplasm

inside cell, reverse transcriptase makes complementary strand of DNA from viral RNA template

double stranded DNA is made & inserted into human DNA

viral proteins assembled into new viruses which bud from cell & go on to infect other cells

latency period = when HIV drops after initial infection to lower level, no symptoms felt for years

AIDS

initial symptoms = minor infections of mucous membranes, recurring respiratory infections

as AIDS progresses, more severe infections occur e.g. tuberculosis, chronic diarrhoea

late stage AIDS = very low no Th cells, serious infections e.g. toxoplasmosis of brain & candidiasis of respiratory system

viruses

antibiotics kill bacteria by interfering with metabolic reactions - target bacterial enzymes & ribosomes

viruses dont have enzymes & ribosomes of their own therefore are unaffected by antibiotics

anti-viral drugs target the few virus-specific enzymes e.g. reverse transcriptase

currently no cure for HIV but anti-viral drugs can slow down progression