topic 2 - cells Flashcards
how can you tell a cell is in anaphase
chromatids at opposite poles of cell
v shape shows sister chromatids have been pulled apart at their centromeres
what is the cell cycle
gap phase 1 - cell grows and new organelles and proteins are made
synthesis - cell replicates its DNA
gap phase 2- cell keeps growing and proteins needed for cell division are made
mitosis
what happens during interphase
cell prepares to divide, DNA is unravelled and replicated to double its genetic content. the organelles are replicates so it has spare ones and its ATP content is increased
what happens during prophase
the chromosomes condense getting shorter and fatter, becoming visible. tiny bundles of protein called centrioles start moving to opposite ends of the cell, forming a network of protein fibres across it called the spindle. the nuclear envelope breaks down and chromosomes lie free in the cytoplasm
what happens during metaphase
chromosomes (each with two chromatids) line up along the middle of the cell and become attached to the spindle by their centromere
what happens during anaphase
the centromeres divide, seperating each pair of sister chromatids. the spindles contract pulling chromatids to opposite poles of the spindle, centromere first. this makes the chromatids appear v shaped
what happens during telophase
the chromatids reach the opposite poles on the spindle and uncoil, becoming long and thin. a nuclear envelope forms around each group of chromosomes, so there are now two nuclei. division of the cytoplasm finishes in telophase, producing two identical daughter cells
what is the division of the cytoplasm called and when does it start
cytokinesis (starts in anaphase ends in telophase)
describe binary fission in bacteria
1) circular DNA and plasmids replicate
(DNA loop only replicated once)
2) cell gets bigger and DNA loops move to opposite poles of cell
3) cytoplasm divides and new cell wall forms
how are algal cells different to plant cells
chloroplast structure is different, could only have 1 large chloroplast
what are the differences between fungal and plant cells
fungal’s cell walls made of chitin not cellulose
they dont have chloroplasts as they don’t photosynthesise
function of cell surface membrane
d- mainly made of lipids and protein
regulates movement of substances into and out of the cell, it has receptor molecules on it which allow it to respond to hormones
function of nucleus
site of DNA replication and transcription (making mRNA)
contains genetic code for each cell
function of nucleolus
makes ribosomes and site of RNA production
description of mitochondria’s components
oval shaped and double membraned, inner membrane folds to form cristae
inside is the matrix which contains enzymes involved in respiration
what are antigens
foreign proteins that can generate an immune response when detected by the body, found on surface of cells
what are pathogens
organisms that cause disease (bacteria,viruses,fungi) and have antigens on their surface
what are abnormal body cells
cancerous or pathogen infected cells that have abnormal antigens on their surface
what are toxins
poisons produced by pathogens
why do bodys reject organ transplants
the cells will have antigens that are different to your own so the foreign antigens trigger an immune response, leading to rejection of the organ
what are the main stages of immune response
1) phagocytosis
2) t cells
3) b cells
steps of phagocytosis
1) phagocyte recognises foreign antigens on a pathogen
2) cytoplasm of phagocyte moves round the pathogen, engulfing it
3) pathogen now contained in PHAGOCYTIC VESICLE in cytoplasm of phagocyte
4) lysosome fuses with phagocytic vacuole and lysozymes break down the pathogen
5) phagocyte presents the pathogens antigens on cell membrane to activate other immune system cells
describe the function of T cells
they are white blood cells with receptor proteins on its surface that bind to complementary antigens presented by phagocytes, activating T cell.
helper T cells - release chemical signals that activate and stimulate cytotoxic T cells which kill abnormal cells
describe the function of B cells
coveried with antibodies (proteins that bind with antigens to form an antigen-antibody complex) and when they bind it activates the B cell to divide into plasma cells
describe antibody production and destruction of pathogens
plasma cells secrete antibodies specific to antigen (monoclonal) which bind to the antigen on the surface of the pathogen.
antibody has 2 binding sites so can clump pathogen together by agglutination
phagocytes bind to antibodies and phagocytose many pathogens at once
describe primary immune response
primary response is slow as there aren’t many B cells that can make the antibody needed to bind to it, eventually the body will produce enough of the right antibody to overcome the infection. infected person shows symptoms of disease
describe secondary immune response
-both T and B cells produce memory cells once exposed to antigen
-memory T cells remember specific antigen and will recognise it a second time round
-memory B cells record specific antibodies needed to bind to antigen
-person now immune and pathogen is gone before they show symptoms
suggest investigations that should be done before a drug is tested on patients
-healthy human volunteers
-other mammals
-investigate different conc of drug to find a safe dosage
what is active immunity
where your immune system makes its own antibodies after being stimulated by an antigen
natural- becoming immune from catching a disease
artificial- becoming immune after you’ve been given a vaccination exposing you to antigen
what is passive immunity
where you are given antibodies made by a different organism
natural- babies becoming immune due to the antibodies it recieves from its mother in placenta and breast milk
artificial- becoming immune after being injected with antibodies from someone else (blood donations)
4 differences between active and passive immunity
active requires exposure to antigen, passive doesn’t
active takes a while for protection to develop, passive is immediate
active memory cells are produced, passive they aren’t
active protection is long term as antibody is produced, passive is short term as antibodies given are broken down
what is a vaccine
a small sample of attenuated pathogen
ethical issues surrounding use of vaccines
-tested on animals
-volunteers may put themselves at unnecessary risk of contracting a disease because they think theyre protected from testing the vaccine
-some people don’t want to take the vaccine due to risk of side effects but are still protected from HI- others think this is unfair
what is antigenic variation
different antigens are formed on the surface of pathogens due to changes in the genes of it
what are monoclonal antibodies
antibodies produced from a single group of genetically identical B cells (plasma cells)
how do cancer drugs not affect normal cells
cancer cells have antigens called tumour markers which are not on normal cells so monoclonal antibodies can be made to attach to these specifically and can carry drugs to only cancer cells
describe how a pregnancy test works
1) application area contains antibodies that are complementary to HCG protein bound to a coloured bead
2) when urine is applied to application area any HCG will bind to antibodies and urine moves up stick to test strip
3) test strip contains antibodies to HCG that are immobilised and if there is HCG present the test strip turns blue because the immobilised antibodies bind to any HCG, concentraing the HCG antibody complex
4) no HCG present, beads will not bind and pass through
describe an Elisa test
1) apply sample containing antigen to well and leave to stick
2) wash well to remove any antigens that didnt stick
3) add an antibody which is specific for the antigen and wait for the antibodies to stick to antigens, wash to remove excess antibodies
4) add a second antibody which will stick to first antibody and is attached to an enzyme molecule, wash to remove excess 2nd antibodies
5) add substrate (colourless) which enzyme will turn into a coloured molecule
intensity of colour= how many antigens present
why is an Elisa test repeated at different dilutions
all of the antigens may not stick to the well and therefore antigen quantity cannot be accurately measured
ethical issues surrounding use of monoclonal antibodies
animals are used to produce cells from which the monoclonal antibodies are produced, some people disagree with this
what is AIDS and why does HIV lead to AIDS
AIDS is a condition where the immune system deteriorates and eventually fails
HIV infects and eventually kills helpers T cells (these send chemical signals that activate phagocytes, cytotoxic T cells and helper B cells) so they’re hugely important for the immune response
symptoms of HIV and AIDS
HIV - flu like symptoms
latency period: no symptoms
AIDS - minor infections of mucuous membranes
-chronic diarrhoea and severe bacterial infections
-candidiasis of respiratory system
describe HIV structure
core - reverse transcriptase and RNA
surrounded by capsid protein
surrounded by envelope, made of membrane stolen from cell membrane of a previous host cell
attachment proteins stick out of envelope
describe how HIV replicates
1) attachment protein attaches to receptors on the cell membrane of host helper T cell
2) capsid released into cell where it uncoats and releases RNA into cytoplasm
3) reverse transcriptase is used to make complementary DNA from viral RNA template
4) double stranded DNA is made and inserted into human DNA
5) host cell enzymes make viral proteins from the viral DNA
6) viral proteins are assembled into new viruses which are released from the cell
how do antibiotics work
kill bacteria by interfering with metabolic reactions by targeting the bacterial enzymes and ribosomes
viruses dont have their own enzymes or ribosomes, they use the ones in host cells, so antibiotics cannot inhibit them
most antiviral drugs are designed to target the few viral specific enzymes
what is the cell membrane mainly made of
phospholipids, proteins and carbohydrates
what does the Fluid Mosaic Model show
-phospholipid molecules form a continuous bilayer which is fluid as they are constantly moving
-channel and carrier proteins scattered through bilayer which allow large molecules and ions to pass through membrane
-receptor proteins on the membrane surface allow membrane to detect chemicals released from other cells and act on it (eg absorb more glucose)
describe phospholipids
head- hydrophilic
tail- hydrophobic
centre of bilayer is hydrophobic so water soluble substances cannot diffuse through it (eg ions)
describe cholesterols role
-gives membrane stability as it binds to hydrophobic tails so they pack together and make membrane rigid
-not present in bacterial cell membranes
-helps maintain shape of animal cells eg red blood cells
-has hydrophobic regions to further prevent polar substances from passing through
describe membrane permeability at below 0 degrees
-rigid as phospholipids don’t have much energy so cannot move
-channel and carrier proteins denature so permeability increases
-ice crystals may form and pierce the membrane, increasing permeability when it thaws
describe membrane permeability between 0 and 45 degrees
-partially permeable as phospholipids can move around and aren’t tightly packed together
-as temp increases so does permeability as phospholipids gain energy
describe membrane permeability above 45 degrees
-bilayer starts to melt and the membrane becomes more permeable
-water inside cell expands putting pressure on membrane
-carrier and channel proteins denature further increasing permeability
define diffusion
net movement of particles (molecules/ions) from a region where they are more highly concentrated to one where their concentration is lower until evenly distributed
does diffusion require energy
no its passive
factors that affect diffusion rate
surface area: bigger = faster
thickness of exchange surface: thinner = faster
conc gradient: higher = faster
what is faciliated diffusion and its conditions
diffusion of larger/charged molecules
-passive
-requires channel or carrier proteins
describe how carrier proteins carry out faciliated diffusion
1) large molecule attaches to carrier protein in membrane
2) protein changes shape
3) releases molecule on other side of membrane
describe how channel proteins carry out faciliated diffusion
form pores in the membrane for charged particles to diffuse through
two differences between channel and carrier proteins in facilitated diffusion
channel-only involved in facilitated diffusion and osmosis
carrier-also involved in active transport
channel- substances pass straight through a water filled pore
carrier- substances bind to carrier protein then it changes shape
factors affecting rate of facilitated diffusion
conc gradient: higher=faster
amount of proteins: less proteins=slower rate
define osmosis
the net movement of water from a high water potential to a low water potential through a partially permeable membrane
define water potential
potential of water molecules to diffuse out of/into a solution
what is pure waters water potential and how can it be affected
0
adding solute reduces water potential e.g squash
what are two solutions with the same water potential called
isotonic
describe movement of water in isotonic conditions
no net movement of water
describe movement of water in hypotonic conditions
solution has higher water potential than cell
cell swells as water moves into cell
describe movement of water in hypertonic conditions
water potential higher in cell than in solution
cell shrinks as water moves out of cell
factors that affect rate of osmosis
water potential gradient: higher = faster
thickness of exchange surface
surface area of exchange surface
describe active transport and its conditions
-uses energy to move molecules and ions across plasma membranes
-usually against conc gradient
-involves carrier proteins or co transporters
how do carrier proteins carry out active transport and what are the 2 main differences between this and facilitated diffusion
molecule attaches to it
protein changes shape
released on other side of membrane
active transport goes against conc gradient usually, facilitated diffusion goes down
active transport requires energy, facilitated diffusion is passive
what source of energy does active transport use
ATP -> ADP + P
creates energy
how do co transporters work
binds 2 molecules at a time as the concentration gradient of 1 of the molecules can help the other to move against its concentration gradient
describe co transport of glucose
1) sodium ions are actively transported out of epithelial cells in the ileum into the blood by the sodium potassium pump, this creates a conc gradient as there is now more sodium ions in the lumen than in the cell
2) sodium ions diffuse from lumen into epithelial cell down conc gradient, taking glucose molecules with it against its conc gradient. conc of glucose increases in cell
3) glucose diffuses out of cell into blood down its conc gradient through a protein channel by facilitated diffusion
what factors affect rate of active transport
speed of carrier proteins
amount of carrier proteins available
availability of ATP depending on rate of respiration
what is an antibody
a protein specific to an antigen produced by B cells
difference of light microscope and electron
electron- higher resolution and use beam of electrons focused by electromagnets inside vacuum environment
light- lower resolution as longer wavelength of light
how does TEM work
beam of electrons passes through a specimen and areas that absorb electrons appear darker
how does SEM work
beam of electrons passes across surface and scatters, building a 3d image
limitations of electron microscopes
living specimens can’t be observed in a vacuum
complex staining process required which may introduce artifacts into the image
specimens have to be very thin so electrons can pass through
SEM has lower resolving power than TEM, better resolution
describe cell fractionation
1) break open cells and filter (homogenise)
2) in ice cold, isotonic, buffered solution
3) spin in centrifuge and remove densest organelle
4) spin again faster,
why should homogenate be ice cold
to reduce enzyme activity so organelles aren’t digested
why should homogenate be isotonic
prevents osmosis so prevents organelles from bursting
why should homogenate be buffered
maintains pH so prevents denaturing of enzymes
structure and function of rough endoplasmic reticulum
folded membranes called cisternae, ribosomes on them
protein synthesis
structure and function of smooth endoplasmic reticulum
folded membranes called cisternae
stores lipids and carbohydrates
structure and function of golgi apparatus and vesicles
add carbohydrates to proteins to form glycoproteins
produce secretory enzymes
secrete carbohydrates
transport, modify and store lipids
form lysosomes
products transported in golgi vesciles where they fuse with the membrane and are released
folded membrane cisternae
secretary vesicles pinch off from cisternae
structure and function of lysosomes
bag of digestive enzymes
fuse with vesicle
release hydrolytic enzymes eg lysozymes
structure and function of mitochondria
cristae, matrix, double membraned, 70s ribosomes, DNA
aerobic respiration
ATP production
DNA to code for enzymes needed in resp
function of ribosomes
site of protein synthesis
structure and function of vacuole
filled with fluid surrounded by a single membrane called a tonoplast
make cells turgid and therefore provide support
temporary store of sugar and amino acids
the pigments may colour petals to attract pollinators
structure and function of chloroplasts
double membrane, stroma, thylakoid, granum, ribosomes
site of photosynthesis
structure and function of cell wall
plants- made of microfibrils of the cellulose polymer
fungi- made of chitin, a nitrogen containing polysaccharide
provides structural strength to the cell
role of organelles in production transport and release of proteins from cells
-DNA in nucleus is code for protein
-ribosomes produce protein
-mitochondria produce ATP for protein synthesis
-golgi apparatus package/modify
-vesicles transport
one difference between eukaryotic cell wall and prokaryotic
eukaryotic- made of cellulose
prokaryotic- made of murein
how can you make a temporary mount of a piece of plant tissue
-add drop of water to glass slide
-obtain thin section of plant tissue and place on slide
-stain with iodine in potassium iodide
-lower cover slip using mounted needle
why do you use a thin section of plant tissue when making a slide
so light can pass through it
why do you obtain plant tissue from the bottom of the root
this is where cells will be dividing so can observe mitosis
what is a homologous pair
two chromosomes that carry the same genes
2 features of an organisms absorption specialised cell
folded membrane so large surface area
large number of carrier proteins so faster rate
large number of mitochondria to make more ATP
what is tissue fluid
liquid that surrounds your cells in the body containing water glucose etc
what cells can generate an immune response
cancer cell
cells from transplants
pathogens
own cells infected by virus
what are antibodies
proteins specific to antigens produced by B cells
