topics 1-4 Flashcards
(297 cards)
1
Q
monomers
A
smaller units from which larger molecules are made
2
Q
examples of monomers
A
monosaccharides, amino acids, nucleotides
3
Q
polymers
A
molecules made from a large number of monomers joined together
4
Q
examples of polymers
A
polysaccharides, proteins, DNA
5
Q
condensation reaction
A
joins two molecules; removal of a water molecule; forms a chemical bond
6
Q
hydrolysis reaction
A
separates two molecules; requires the addition of a water molecule; breaks a chemical bond
7
Q
monosaccharides
A
single sugar molecules (e.g., glucose, fructose, galactose).
8
Q
disaccharides
A
formed by the condensation of two monosaccharides
(e.g., glucose + glucose = maltose, glucose + fructose = sucrose, glucose + galactose = lactose)
9
Q
polysaccharides
A
formed by the condensation of many monosaccharides
(e.g., starch, glycogen, cellulose);
releases water;
forms glycosidic bonds
10
Q
glycogen
A
store of glucose in animals; formed from α-glucose; more branches (1-6 gd bonds) than amylopectin (increases SA and allows enzymes to work simultaneously and hydrolyse it back into glucose); large and compact maximising the amount of energy it can store; insoluble means it will not affect the water potential and cannot diffuse out of cells
11
Q
starch
A
amylose and amylopectin; store of glucose in plants
12
Q
amylose
A
formed by a condensation reaction;
long, unbranched helix of alpha-glucose;
forms 1-4 glycosidic bonds;
coils up to form a helix (compact; stores a lot of energy-glucose)
13
Q
amylopectin
A
formed by condensation reaction;
long, branched chain of alpha-glucose;
more ends for hydrolysis
forms straight chains of 1-4 glycosidic bonds and branches out with 1-6 glycosidic bonds (increases surface area)
14
Q
cellulose
A
for structural strength of plant cell wall;
formed from β-glucose;
each alternate glucose is inverted;
formed by many condensation reactions and 1-4 gd bonds;
creates a long, straight chain;
the chains line up parallel to each other, held in place by H bonds which are individually weak, but collectively strong (fibril)
15
Q
triglycerides
A
formed via condensation reactions between glycerol and three fatty acids, forming ester bonds;
used as an energy storage molecules;
properties: high ratio of C-H bonds to C atoms, insoluble in water (forms droplets).
16
Q
phospholipids
A
formed via condensation reactions between glycerol, two fatty acids, and a phosphate group;
forms phospholipid bilayer in cell membranes;
properties: hydrophilic phosphate heads, hydrophobic fatty acid tails
the centre of the bilayer is hydrophobic so water-soluble molecules can’t easily pass through-the membrane acts as a barrier
17
Q
saturated and unsaturated fatty acids
A
saturated: no C=C double bonds;
unsaturated: one or more C=C double bonds
18
Q
emulsion test for lipids
A
add ethanol and shake (dissolves lipids) then add water;
positive result: milky/cloudy white emulsion
19
Q
biuret test for proteins
A
add biuret solution (sodium hydroxide + copper (II) sulfate)
positive result: purple color (negative result: stays blue)
20
Q
amino acids
A
monomer of proteins
21
Q
dipeptide
A
two amino acids joined by a peptide bond
22
Q
polypeptide
A
many amino acids joined by peptide bonds
23
Q
primary structure
A
sequence of amino acids in polypeptide chain
24
Q
secondary structure
A
hydrogen bonding causes folding into alpha-helix or beta-pleated sheet
25
tertiary structure
3D structure held by interactions between side chains (ionic bonds, disulfide bridges, hydrogen bonds)
26
ionic bonds in tertiary structure
form between the carboxyl and amino groups not involved in the peptide bonds;
weaker than disulfide bridge
27
disulfide bridges in tertiary structure
whenever two molecules of cysteine (amino acid) come close together; the S atom in one cysteine bonds to the S atom in the other cysteine
28
quaternary structure
the quaternary structure is the way the polypeptide chains are assembled tg
29
how do enzymes speed up reactions
enzymes lower the activation energy by providing alternative pathway
30
lock and key model
active site is a fixed shape/doesn’t change shape;
it is complementary to one substrate;
after a successful collision, an enzyme-substrate complex forms leading to reaction
31
induced fit model
1. before reaction, enzyme active site not completely complementary to substrate/ doesn’t fit substrate
2. active site shape changes as substrate binds and enzyme-substrate complex forms
3. this stresses / distorts bonds in substrate leading to a reaction
32
how does enzyme concentration affect the rate of enzyme-controlled reactions
there are more active sites for the substrates to bind to
however, its only applicable to a certain extent;
at some point, enzyme activity will plateau because there are too many active sites and not enough substrates
33
how does temperature affect the rate of enzyme-controlled reactions
rate of reaction increases as particles gain more kinetic energy;
leading to more collisions;
if temperature is too high enzymes denature
34
how does pH affect the rate of enzyme-controlled reactions
at very acidic and alkaline pH values the shape of the enzyme is altered so that it is no longer complementary to its specific substrate
35
competitive inhibitors
have a similar shape to substrate;
compete with the substrate molecules to bind to the active site but no reaction takes place
36
what happens when there's a higher concentration of competitive inhibitors
if there's a higher conc of inhibitors, it will take up nearly all active sites and hardly any of the substrate will get to the enzyme
37
what happens when there's a higher concentration of substrates
if there's a higher conc of substrates, the substrates chance of getting to an active site before the inhibitor increases
*increasing substrate conc increases rate of reaction*
38
non-competitive inhibitors
they bind to the enzyme away from its active site which causes the active to change shape so the substrate molecules can no longer bind to it
39
what happens when you increase the substrate concentration when non-competitive inhibitors are present
has no effect because non-competitve inhibitors don't compete with the substrate molecules to bind to the active site because they are a different shape;
inhibits enzyme activity
40
DNA
double-stranded helix, holds genetic information (ACGT)
41
RNA
single-stranded, transfers genetic information from DNA to ribosomes (ACGU)
42
nucleotide
*DNA and RNA are polymers of nucleotides*
nucleotides are made from: a pentose sugar (sugar with 5 C atoms) and phosphate group (sugar-phosphate backbone and a nitrogen-containing base (ACGT)
43
polynucleotide structure
nucleotides join tg to form polynucleotides via a condensation reaction between phosphate group of one nucleotide and the sugar of another;
form a phosphodiester bond
44
DNA structure
double-helix;
composed of two polynucleotides joined tg by H bonds between complementary bases;
(a+t, c+g)
45
complementary base pairing
adenine pairs with thymine (2 H bonds)
guanine pairs with cytosine (3 H bonds)
equal amounts of A+T and C+G
46
RNA structure
a pentose sugar (sugar with 5 C atoms) and phosphate group (sugar-phosphate backbone and a nitrogen-containing base (ACGU)
47
difference between DNA and RNA
1. deoxyribose/ribose
2. thymine/uracil
3. double strand/single strand
4. long/short
48
how does DNA replicate?
semi-conservative replication
49
what does semi-conservative replication mean?
half of the strands in the new DNA are from the original DNA molecule;
leads to genetic continuity
50
semi-conservative replication (process)
1. DNA helicase breaks the H bonds between bases on the two polynucleotide strands (helix unwinds)
2. each original single strand acts as a template for a new strand; complementary base pairing makes free-floating DNA nucleotides are attracted to their complementary exposed bases from original template strand
3. condensation reactions join the nucleotides of the new strands together catalysed by DNA polymerase; H bonds form between the bases
4. each new DNA molecule contains one strand from the original DNA molecule and one new strand
51
meselson+stahl experiment
used 2 isotopes of N to show that DNA replicates using semi-conservative replication
(heavy-15);(light-14)
1. grow 2 samples of bacteria (one in lightN broth and one in heavyN broth)
2. sample of DNA taken from each batch and spun in centrifuge
3. bacteria grown in heavyN broth taken out and put in lightN broth and left for one round of DNA replication
4. DNA settled in the middle, mixture of both heavyN and lightN
52
ATP
adenosine triphosphate;
immediate source of energy for metabolic reactions
53
what is ATP made up of?
one adenine base, ribose sugar and 3 phosphate groups (ATP synthase)
54
where is the energy in ATP stored?
stored in high energy bonds between the phosphate groups and is released via hydrolysis reactions
ATP → ADP + Pi (ATP hydrolase)
55
properties of water
high specific heat capacity: stable temperature for organisms
high latent heat of evaporation: efficient cooling mechanism
cohesion: surface tension, water transport in plants
solvent: dissolves ionic compounds and other substances, medium for metabolic reactions
metabolite: involved in hydrolysis and condensation reactions
56
phosphate (inorganic ion)
DNA/RNA backbone;
energy storage/release in ATP
57
hydrogen (inorganic ion)
pH regulation;
impacts enzyme and haemoglobin function
58
iron (inorganic ion)
transports oxygen with haemoglobin
59
sodium (inorganic ion)
Na+, involved in cotransport of glucose and amino acids
60
cell surface membrane
phospholipid bilayer with embedded proteins; selectively permeable; barrier between internal and external environments
61
nucleus
nuclear envelope (double membrane), nuclear pores, nucleolus, DNA/chromatin;
controls the cells activities through transcription;
nuclear pores allow substances to move between nucleus and cytoplasm(mRNA);
nucleolus makes ribosomes which are made up of proteins and ribosomal RNA
62
mitochondria
double membrane; inner membrane folded to form cristae;
matrix contains small 70s ribosomes, small circular DNA and enzymes involved in glycolysis;
site of aerobic respiration to produce ATP
63
golgi apparatus
modifies proteins to glycoproteins (adds carbs) from RER; packages glycoproteins into vesicles for transport; produces secretory enzymes; transports, modifies and stores lipids, forms lysosomes
64
lysosomes
hydrolyse material injested by phagocytic cells, releases enzymes to the outside of the cell in order to destroy material around the cell, digest worn out organelles so that the useful chemicals they are made of can be reused, completely break down cells after they have died (autolysis)
65
ribosomes
made of RNA and proteins, float free in cytoplasm or bound to RER; not membrane bound; site of translation
66
RER
ribosomes bound to a system of folded membranes; folds polypeptides to secondary/tertiary structure; modifies proteins to glycoproteins; packages to vesicles, transport to the golgi apparatus
67
SER
system of folded membranes; synthesises, stores and transports lipids and carbs, packaged into vesicles
68
chloroplasts
chloroplast envelope is a double plasma membrane that surrounds the organelle (highly selective); thylakoid membranes stacked to form grana which is linked by lamellae (th contains chlorophyll); stroma is a fluid filled matrix where second stage of photosynthesis occurs, contains starch grains
chlorophyll absorbs light for photosynthesis to produce organic substances
69
cell wall
made of cellulose in plants and algae; chitin in fungi;
rigid structure, prevents the cell changing shape and bursting
provides mechanical strength to avoid cell lysis under osmotic pressure
70
vacuole
fluid filled sac bounded by a single membrane; contains cell sap; surrounding membrane is tonoplast;
maintains pressure in the cell
makes cells turgid, sugars and amino acids act as a temporary food store, pigments attract pollinating insects
71
differences in prokaryotic cells
no membrane bound organelles;
no nucleus, circular DNA, not associated with proteins;
cell wall is made of murein;
70s ribosomes;
one or more plasmids
72
scanning electron microscope
uses electrons to form a 2D image;
beam of electrons scan surface;
shorter wavelength so higher resolution; x1500000 magnification
73
transmission electron microscope
uses electrons to form a 3D image; electromagnets focus beam of electrons onto specimen, more dense=more absorbed=darker;
shorter wave,entry of electrons; x1500000 magnification
74
magnification vs resolution
how much bigger the image of a sample is compared to the real size; magnification
how well distinguished an image is between 2 points; resolution
75
viruses
acellular; not made of/cannot divide into cells
non-living; unable to exist/reproduce without a host cell
76
cell fractionation (describe)
1. homogenisation–>grinding up the cells in a blender
CONDITIONS:
>ice cold
>isotonic (solution has same water potential as cells)
>have a buffer added
2. filtration (through a gauze)
3. ultracentrifugation–>separate organelles by mass-density
>filtered solution centrifuged at low speed
>respin supernatant at higher speed
> process repeated at higher speeds
77
cell fractionation (explain)
1. homogenisation–> break opens the cells, breaking up the plasma membrane to release the organelles
> ice cold: reduces enzyme activity, preventing organelles from being broken down
> isotonic solution: prevents damage to organelles by osmosis (prevents organelle lysis)
>have a buffer added: maintain pH of a solution to prevent proteins denaturing
2. filtration–>take out debris e.g. connective tissue and whole cells
3. ultracentrifugation
>centrifuge at low speed–separate out heaviest organelles e.g. nuclei
>respin at higher speed– remove heaviest organelles from supernatant e.g. chloroplast into the pellet
>process repeated at higher speeds–to remove the heaviest organelles in pellets each time
78
stages of cell cycle
interphase (synthesis; G1; G2), mitosis (PMAT), cytokinesis
79
interphase
>G1: cell enlarges; volume and mass increases (more organelles);
more mitochondria (needed to produce ATP and release energy to allow the spindle fibres to pull the chromosomes to opposite sides of the cell)
>S phase: DNA replicates semi-conservatively leading to two sister chromatids
>G2: cell keeps growing and protein synthesis increases to make spindle fibres for mitosis
80
mitosis (meaning)
parent cell divides = two genetically identical daughter cells
81
prophase
chromosomes condense, becoming shorter, thicker and more visible; appear as two sister chromatids joined by a centromere
nuclear envelope breaks down and centrioles move to opposite poles forming spindle network
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metaphase
chromosomes align along equator; spindle fibres attach to chromosomes by centromeres
83
anaphase
spindle fibres contract, pulling sister chromatids to opposite poles of the cell; centromere divides;
chromatids appear v shaped
84
telophase
chromosomes uncoil, becoming longer and thinner;
nuclear envelope reforms = two nuclei;
spindle fibres and centrioles break down
85
cytokinesis
division of the cytoplasm, producing two new cells
86
importance of mitosis
parent cell divides to produce 2 genetically identical daughter cells for…
- growth of multicellular organisms by increasing cell number
- repairing damaged tissues / replacing cells
- asexual reproduction
87
result of uncontrolled division
uncontrolled cell division can lead to the formation of tumours and of cancers
- malignant tumour – cancerous – spreads and affects other tissues / organs
- benign tumour – non-cancerous
88
binary fission
circular DNA and plasmids replicate (circular DNA replicates once, plasmids can be replicated many times);
cytoplasm expands (cell gets bigger) as each DNA molecule moves to opposite poles of the cell;
cytoplasm divides = 2 daughter cells, each with a single copy of DNA and a variable number of plasmids
89
viral replication
1. attachment protein binds to complementary receptor protein on surface of host cell
2. inject nucleic acid (DNA/RNA) into host cell
3. infected host cell replicates the virus particles
90
fluid mosaic model of cell surface membrane
molecules within membrane can move laterally (fluid) e.g. phospholipids;
mixture of phospholipids, proteins, glycoproteins and glycolipids
91
structure of cell surface membrane
phospholipid bilayer;
phosphate heads are hydrophilic so attracted to water;
fatty acid tails are hydrophobic so repelled by water;
embedded proteins;
channel and carrier proteins;
glycolipids (lipids and attached polysaccharide chain) and glycoproteins (proteins with polysaccharide chain attached);
cholesterol (binds to fatty acid tails)
92
phospholipid bilayer
allows movement of non-polar small/lipid-soluble molecules e.g. oxygen or water, down a concentration gradient (simple diffusion);
restricts the movement of larger/polar molecules
93
channel proteins
allows movement of water-soluble/polar molecules / ions, down a concentration gradient (facilitated diffusion)
94
carrier proteins
allows movement of water-soluble/polar molecules / ions, down a concentration gradient (facilitated diffusion);
allows the movement of molecules against a concentration gradient using ATP (active transport)
95
features of the plasma membrane adapt it for its other functions
phospholipid bilayer; maintains a different environment on each side of the cell
phospholipid bilayer is fluid; can bend to take up different shapes for phagocytosis / to form vesicles
surface proteins (glycoproteins / glycolipid) ; used for cell recognition / act as antigens
cholesterol; regulates fluidity / increases stability
96
role of cholesterol
makes the membrane more rigid / stable / less flexible, by restricting lateral movement of molecules making up membrane e.g. phospholipids (binds to fatty acid tails causing them to pack more closely together)
note: not present in bacterial cell membranes
97
what is ventilation needed for
maintains an oxygen concentration gradient
-brings in air containing higher concentration of oxygen
-removed oxygen with lower concentration of oxygen
98
gas exchange in alveoli (oxygen)
oxygen diffuses from alveoli down its concentration gradient;
across the alveolar epithelium;
across the capillary endothelium;
into the blood
99
gas exchange in alveoli (oxygen)
oxygen diffuses from alveoli down its concentration gradient;
across the alveolar epithelium;
across the capillary endothelium;
into the blood
100
features of alveolar epithelium
thin/one cell thick: short dp and fast diffusion;
large SA:V: fast diffusion;
permeable;
good blood supply from capillaries: maintains concentration gradient;
elastic tissue: recoils after expansion
101
adaptions of lungs
many alveoli/capillaries: large SA for fast diffusion;
thin walls (A/C): short dp for fast diffusion;
ventilation: maintains concentration gradient for fast diffusion
102
inspiration
external IM contract, internal IM relax;
ribcage moves up and out;
diaphragm muscles contract/flatten;
increasing volume and decreasing pressure in thoracic cavity;
atmospheric pressure higher than pressure in lungs;
air moves down pressure gradient into lungs;
ACTIVE PROCESS
103
expiration
internal IM contract, external IM relax;
ribcages moves down and in;
diaphragm relaxes and moves upwards;
decreasing volume and increasing pressure in thoracic cavity;
atmospheric pressure lower than pressure in lungs;
air moves down pressure gradient out of lungs;
PASSIVE PROCESS
104
tidal volume
volume of air in each breath
105
ventilation rate
number of breaths per minute
106
forced expiratory volume (FEV)
maximum volume of air that can be breathed out in 1 second
107
forced vital capacity (FVC)
maximum volume of air possible to breathe forcefully out of lungs after a deep breath in
108
fibrosis
scar tissue in lungs; thicker and less elastic;
diffusion distance increased; rate of diffusion decreased; faster ventilation rate to get enough oxygen;
lungs can expand and recoil less (can’t hold as much air);
reduced tidal volume and FVC
109
asthma
inflamed bronchi;
asthma attack= smooth muscle lining bronchioles contracts;
constriction of of airways-narrow diameter; airflow reduced (FEV);
less oxygen enters alveoli/blood;
reduced rate of gas exchange - less oxygen diffuses into the blood - cells receive less oxygen - rate of aerobic respiration - less energy released = fatigue, weakness
110
digestion
large biological molecules are hydrolysed into smaller molecules that can be absorbed
111
digestion of starch (polysaccharides)
amylase hydrolyses starch to maltose;
maltase hydrolyses maltose to glucose;
hydrolysis of glycosidic bond
amylase produced by salivary glands, released into mouth;
amylase produced by pancreas, released into small intestine
112
digestion of lipids
bile salts emulsify lipid to smaller lipid droplets (increases SA to speed up action of lipases);
lipase hydrolyses lipids to monoglycerides and fatty acids;
breaking ester bond;
monoglycerides, fatty acids and bile salts stick together to form micelles
bile salts produced by the liver;
lipase made in the pancreas, released to small intestine
113
digestion of proteins
endopeptidases;
-hydrolyses peptide bonds between amino acids in the central region; breaking protein into two two or more smaller peptides
exopeptidases;
-hydrolyse peptide bonds at the ends of protein molecules; removing a single amino acid
dipeptidases;
-hydrolyses peptide bond between a dipeptide
114
circulatory system
general pattern of blood circulation;
involves lungs, pulmonary artery/vein, aorta, vena cava, hepatic artery/vein, renal vein/artery, coronary arteries
115
double circulatory system
blood passes through heart twice for each complete circulation of body
116
pulmonary circulation
deoxygenated blood in right side of heart pumped to lungs; oxygenated blood returns to left side of the heart
117
systematic circulation
oxygenated blood in left side of heart pumped to tissues/ organs of body; deoxygenated blood returns to the right side
118
why is a double circulatory system important
prevents mixing of oxygenated and deoxygenated blood; ensures full oxygen saturation of blood going to the body for respiration
119
coronary arteries
deliver oxygenated blood to cardiac muscle
120
aorta
takes oxygenated blood from heart to respiring tissue
121
vena cava
takes deoxygenated blood from respiring tissues to heart
122
pulmonary artery
takes deoxygenated blood from the heart to lungs
123
pulmonary vein
takes oxygenated blood from the lungs to heart
124
renal arteries
takes oxygenated blood to kidneys
125
renal veins
take deoxygenated blood from the kidneys to the vena cava
126
structure of the heart related to its function
atrioventricular valves
-prevent backflow of blood from ventricles to atria
semi lunar valves
-prevent backflow of blood from arteries to ventricles
left ventricle has thicker muscular wall
-generates higher blood pressure
-oxygenated blood has to travel greater distance around the body
right has thinner muscular wall
-generates lower blood pressure (high pressure would damage alveoli)
-deoxygenated blood travels a smaller distance to the lungs
127
structure of arteries in relation to their function
carries blood from heart to rest of body at high pressure
-thick, smooth muscle layer; contracts pushing blood along; controls blood flow/pressure
elastic tissue layer
-stretch as ventricle contracts and recoils as ventricle relaxes; reduces pressure surges
thick wall
-withstands high pressure and prevents artery bursting
smooth, thin endothelium
-reduces friction
narrow lumen
-increases and maintains high blood pressure
128
arterioles
division of arteries to smaller vessels which can direct blood to specific capillaries/ areas
129
structure of arterioles in relation to its function
thicker muscle layer than arteries
-constricts to reduce blood flow by narrowing lumen; dilates to increase blood flow by enlarging lumen
thinner elastic layer for lower pressure surges
130
structure of veins in relation to in function
wider lumen than arteries; very little elastic and muscle tissues; valves to prevent backflow of blood; contraction of skeletal muscles squeezes veins, maintaining blood flow
131
structure of capillaries and capillary beds
capillaries allow the efficient exchange of gases and nutrients between blood and tissue fluid;
capillary wall is a thin layer of squamous endothelial cells; short dp for rapid diffusion;
capillary bed is made a large network of branched capillaries; increase SA:V for rapid diffusion;
narrow lumen; reduces flow rate so more diffusion/exchange;
capillaries permeate tissues; short dp;
pores in walls between cells; allows substances to escape
132
atrial systole
atria contract; decreasing volume and increasing pressure inside atria;
AV valves forced open;
blood pushed into ventricles
133
ventricular systole
ventricles contracts from the bottom up; decreasing volume and increasing volume;
SL valves forced forced upon;
AV valves shut;
blood pushed out of heart through arteries
134
diastole
atria and ventricles relax; increasing volume and decreasing pressure inside the chambers;
blood from veins fills atria and flows passively to ventricles;
AV valves open;
SL valves shut
135
cardiac output
amount of blood pumped out of the heart per minute
stroke volume x heart rate
136
stroke volume
volume of blood pumped by the ventricles in each heart beat
cardiac output / heart rate
137
heart rate
number of beats per minute
cardiac output / stroke volume
138
haemoglobin
group of chemically similar molecules found in many different organisms
-chemical structure may differ between organisms e.g. sequence of amino acids
found in rbc
-no nucleus
-biconcave shape; increases SA for rapid diffusion/absorption of oxygen
139
structure of haemoglobin
quaternary structured protein- made of 4 polypeptide chains;
each polypeptide contains a haem group containing an iron (II) ion which combines with oxygen
140
transport of oxygen using haemoglobin
haemoglobin in rbc carries oxygen (oxyhaemglobin);
haemoglobin can carry 4 oxygen molecules-one at haem group
141
transport of oxygen at high pO2
haemoglobin has a high affinity for oxygen;
oxygen readily loads/associates with haemoglobin
142
transport of oxygen at low pO2
oxygen readily unloads/dissociates from haemoglobin;
concentration of CO2 is high so rate of unloading is high
143
simple diffusion
net movement of small, non polar molecules across a partially permeable membrane down its concentration gradient
-passive
144
factors affecting rate of simple diffusion
surface area;
concentration gradient;
diffusion pathway
145
facilitated diffusion
net movement of larger/polar molecules across a partially permeable membrane down its concentration gradient through a transport protein
-passive
146
factors affecting the rate of facilitated diffusion
surface area;
concentration gradient;
number of channel/carrier proteins
147
role of transport proteins
carrier proteins transport large molecules; changes shape when molecule attaches
channel proteins transport charged/polar molecules through its pore
different carrier and channel proteins facilitate the diffusion of different specific molecules
148
active transport
net movement of molecules/ions against a concentration gradient using carrier proteins using energy from ATP
149
factors affecting the rate of active transport
pH/temperature;
speed of carrier protein;
number of carriers proteins;
rate of respiration (ATP production)
150
osmosis
net movement of water molecules across a selectively permeable membrane down a water potential gradient
-passive
151
water potential
the likelihood of water molecules to diffuse out of or into a solution;
pure water has the highest water potential
152
factors affecting the rate of osmosis
surface area;
water potential gradient;
thickness of exchange surface
153
antigen
proteins which can stimulate an immune response
154
antigen allow the immune system to identify..
pathogens;
cells from other organisms of the same species (organs, blood);
abnormal cells (tumours);
toxins released from bacteria
155
phagocytosis
phagocyte recognises foreign antigens on the pathogen and binds to the antigen;
phagocyte engulfs pathogen by surrounding it;
pathogen contained in phagosome and fused with lysosome to release lysozymes;
hydrolyse/digest the pathogen;
antigens presented on cell surface membrane
156
rs between SA:V
rate of heat loss increases as SA:V increases
-more heat lost in smaller organisms
-so they need a higher metabolic rate to generate enough heat to maintain a constant body temperature
157
why do larger organisms need a specialised surface
they have a smaller SA:V and a long diffusion pathway;
and a high demand for oxygen and to remove carbon dioxide
158
adaptions for gas exchange in a single celled organism
-thin, flat shape
-large SA:V
-short diffusion pathway
for rapid diffusion
159
adaptions for gas exchange in the tracheal system
1. air moves through spiracles on the surface
2. air moves through tracheae
3. gas exchange at tracheoles directly to/from cells
-oxygen diffuses to respiring cell
-carbon dioxide diffuses out of respiring cells
160
more adaptions of tracheal system
lots of thin, branching tracheoles;
short diffusion pathway and SA:V;
for rapid diffusion
thick waxy cuticle;
increases diffusion distance;
less evaporation
spiracles can open and close;
open to allow oxygen in, close when water loss too much
rhythmic abdominal movements increases the efficiency of gas exchange by increasing the amount of air/oxygen entering;
maintains greater concentration gradient for diffusion
161
adaptions for gas exchange across the gills of fish
counter current flow
-blood flows through lamellae and water flows over lamellae in opposite directions
-always a higher conc of oxygen in water than the blood it’s near
-hence a conc gradient of oxygen between water and blood maintained along the whole length of lamellae
-equilibrium is never met
-maximises diffusion of oxygen
162
physical adaptions of fish gills
each gill is made of lots of gill filaments which are covered in many lamellae;
gill filaments and lamellae provide a larger surface area;
vast network of capillaries on lamellae; remove oxygen to maintain a concentration gradient;
thin/flattened epithelium; short dp
163
adaptions of gas exchange in leaves
lots of stomata that are close together;
-large SA for gas exchange;
interconnecting air space in mesophyll layer;
-gases come into contact with mesophyll cells;
mesophyll cells have a large SA;
-rapid diffusion;
thin;
-short dp
164
adaptions for gas exchange in xerophytic plants
thick waxy cuticle
-increase diffusion distance; less evaporation
stomata and rolled leaves and hairs
-traps water vapour; water potential gradient decreased; less evaporation
spindles/meedles
-reduces SA:V
165
co-transport (Na+ and glucose)
1. sodium ions actively transported out of epithelial cells lining the ileum into the blood by the sodium-potassium pump; creates a sodium concentration gradient
2. sodium ions and glucose move by facilitated diffusion into the epithelial cell from the lumen via a co transporter protein
3. creates a glucose concentration gradient
4. glucose moves out of cell into blood by facilitated diffusion through a protein channel
166
cohesion-tension theory
water evaporates from the leaves via the stomata due to transpiration;
water potential is reduced and increases water potential gradient;
water drawn out of xylem creating tension;
cohesive forces between water molecules pull water up as a column;
water lost enters the roots via osmosis;
water is moving up against gravity and sticks to the edges of the column
167
isomers
same molecular formula but different structure (alpha-glucose and beta-glucose)
168
RNA function
transfer the genetic code from the DNA in the nucleus to the ribosomes
169
DNA function
used to store your genetic info
170
properties of ATP
1. released in small, manageable amounts so energy is wasted
2. small and soluble and can easily be transported around the cell
3. only one bond needs to be broken to release energy
4. can transfer energy to another molecule by transferring one of its phosphate groups
5. cannot leave the cell, always in immediate supply
171
how does the structure of ATP make it a good source of immediate energy?
the bonds between the phosphate groups have a low activation energy;
this means they can be easily broken;
breaking the bonds releases energy
172
function of ATP
an immediate source of energy for biochemical processes and synthesis of biological molecules
173
antigens
foreign proteins present on the cell-surface membrane that stimulates an immune response;
can mutate to change their tertiary structure so they're not complementary (antigen variation)
174
antigens are specific to allow the immune system to identify...
- pathogens (disease causing organisms) e.g. viruses, fungi, bacteria
- cells from other organisms of the same species e.g. organ transplant, blood transfusion
- abnormal body cells e.g. cancerous cells / tumours
- toxins released from bacteria
175
phagocytosis
1. phagocyte e.g. macrophage recognises foreign antigens on the pathogen and binds to the antigen
2. phagocyte engulfs pathogen by surrounding it with its cell surface membrane / cytoplasm
3. pathogen contained in vacuole/vesicle/phagosome in cytoplasm of phagocyte
4. lysosome fuses with phagosome and releases lysozymes (hydrolytic enzymes) into the phagosome
5. these hydrolyse / digest the pathogen
6. phagocyte becomes antigen presenting and stimulates specific immune response
176
cellular response (T-cell response)
1. T-lymphocytes recognises APCs after phagocytosis (foreign antigen)
2. specific Th cell with receptor complementary to specific antigen binds to it, becoming activated and dividing rapidly by mitosis to form clones which:
a) stimulate B cells for the humoral response
b) stimulate cytotoxic T cells to kill infected cells by producing perforin
c) stimulate phagocytes to engulf pathogens by phagocytosis
177
humoral response (B-cell response)
1. clonal selection:
a) specific B cell binds to antigen presenting cell and is stimulated by helper T cells which releases cytokines
b) divides rapidly by mitosis to form clones (clonal expansion)
2. some become B plasma cells for the primary immune response – secrete large amounts of monoclonal antibody into blood
3. some become B memory cells for the secondary immune response
178
primary response
primary response – antigen enters body for the first time (role of plasma cells)
- produces antibodies slower and at a lower concentration because
- not many B cells available that can make the required antibody
- Th cells need to activate B plasma cells to make the antibodies (takes time)
- so infected individual will express symptoms
179
pathogen
microorganism that causes diseases
179
secondary response
at the second exposure, the immune system produces a quicker, stronger immune response
- clonal selection happens faster
- memory B-cells are activated and divide into plasma cells that produce the right antibody to the antigen
-memory T-cells are activated and divide into the correct type of T-cells to kill the cell carrying the antigen
this response often gets rid of the pathogen before you begin to show symptoms
180
2 types of wbc
lymphocyte and phagocyte
181
why must wbcs be able to differentiate between self and foreign cells?
allows the white blood cells to know what is part of your body, and what is not;
so that the body's own tissues aren't destroyed
182
what is used to identify cells as self or non-self?
proteins on the cell surface membrane
183
what is the immune system able to identify?
1. pathogens (e.g. HIV)
2. non-self material (e.g. cells from another organism);
3. toxins;
4. abnormal body cells (e.g. cancer)
184
what issue may arise with the immune system, due to transplants?
the immune system may recognise the tissues as non-self, and therefore attack transplanted organs/tissues.
185
plasma cells
identical to B-cells (clones);
they secrete loads of antibodies specific to the antigen – monoclonal antibodies – which bind to the antigens on the surface of the pathogen to form antigen-antibody complexes
186
neutrophils
engulf and digest pathogens (and dead human cells/debris)
187
macrophages
can punch holes in the bacteria or stick proteins to the outside of the bacteria to make them more appealing for the neutrophils to destroy
188
role of phagocyte
ingest and destroy pathogens
189
what attracts phagocytes?
chemical products of pathogens, or dead, damaged or abnormal cells
190
what allows phagocytes to recognise and attach to chemicals on the surface of the pathogen?
receptors on the cell-surface membrane
191
T-cell response to being infected by a pathogen
1. phagocyte ingests pathogen
2. pathogen's antigens are placed onto the phagocyte's surface membrane (It becomes an APC)
3. the receptors of a specific Th cell bind perfectly to the antigen being presented
4. this binding activates the Th cell to divide and produce many clones (clonal expansion)
5. these cloned cells specialise
192
in what way might cloned Th cells differentiate?
1. develop into memory cells
2. stimulate phagocytes
3. stimulate B-cells to divide and secrete antibodies
4. activate Tc cells (cytotoxic cells)
193
cell-mediated response
-once a pathogen has been destroyed by a phagocyte, the antigens are positioned on its cell surface and its referred to as an antigen-presenting cell
- helper T-cells have receptors on its surface that attach to the antigens on the APC
- once attached, the T-cells divide by mitosis to replicate and make large numbers of clones
- cloned helper T-cells differentiate into different cells
- some remain as helper T-cells and activate B-lymphocytes
- some stimulate macrophages to perform more phagocytosis
- some become memory cells for that shaped antigen
- some become cytotoxic T-cells (killer T-cells)
194
cytotoxic T-cells
- destroy abnormal or infected cells
- they release a protein (perforin) which embeds in the cell surface membrane and makes a pore so substances can enter and leave a cell, causing the cell death
- most common in viral infections as they affect body cells
195
why are there millions of types of B-cells?
each one creates an antibody to respond to a specific antigen;
the variations in antigens require a large number of different antibodies
196
how is a B-cell stimulated to divide by mitosis?
an activated Th cell binds to the processed antigens on the B cell to stimulate it to divide by mitosis, creating clones;
this is clonal selection
197
what are the antibodies created from cloned B-cells called?
monoclonal antibodies
198
what do memory cells do?
involved in secondary immune response
they last a long time in the body, when they encounter the complimentary antigen to their antibody, they are stimulated to divide rapidly;
this creates lots of memory and plasma cells quickly, and therefore lots of antibodies are created quickly
199
what does an antibody do?
it binds to a specific antigen, which is complimentary to its specific binding site
200
what are antibodies made of?
they are made of 4 polypeptide chains;
2 long (heavy chains), 2 short (light chains)
201
what is the name given to the binding site of an antibody?
the variable region; has a specific tertiary structure
202
what do antibodies do to pathogens?
1. cause agglutination through binding to two pathogens at once; clumps together many pathogens
2. they act as markers to stimulate phagocytosis
203
vesicle
fluid filled sac, transports substances around the cell
204
spiracles
tiny pores along the length of the abdomen;
opened and closed by valves, they usually stay closed to prevent water loss
205
trachea
network of internal tubes; have rings to strangthen them and keep them open
206
207
smaller organisms have…
a higher SA:V so they lose heat more quickly
208
adaptions for larger organisms (gas exchange)
need a specialised surface/organ;
they have a smaller SA:V and long diffusion pathway;
high demand for oxygen and removal CO2
209
process of gas exchange in leaves
CO2/O2 diffuse through the stomata;
stomata opened by guard cells;
CO2/O2 diffuse into mesophyll layer into air spaces;
CO2/O2 diffuse down concentration
210
process of gas exchange in leaves
CO2/O2 diffuse through the stomata;
stomata opened by guard cells;
CO2/O2 diffuse into mesophyll layer into air spaces;
CO2/O2 diffuse down concentration
211
structure of human gas exchange system
trachea
splits into 2 bronchi;
splits into bronchioles;
ends in alveoli;
diaphragm underneath
212
how does gas exchange happen in the alveoli? (O2)
oxygen diffuses from alveoli;
down conc gradient;
across alveolar epithelium;
across capillary endothelium;
into the blood (haemoglobin)
213
how does gas exchange happen in the alveoli? (CO2)
carbon dioxide diffuses from capillary;
down conc gradient;
across alveolar epithelium;
across capillary endothelium;
into alveoli
214
why is ventilation needed?
maintains an oxygen concentration gradient;
brings in air with high O2 conc and removes air with low O2 conc
215
calculating heart rate from cardiac cycle data
one beat=one cardiac cycle;
find the length of one cardiac cycle (human average=0.83 seconds)
heart rate in beats=60 seconds/length of one cardiac cycle
216
how to interpret if semi lunar valves are closed
when pressure in aorta/pulmonary artery is higher than ventricle;
prevents back flow of blood from artery to ventricles
217
how to interpret if semi lunar valves are open
when pressure in ventricle is higher than aorta/pulmonary artery;
blood is flowing from ventricle to aorta
218
how to interpret if atrioventricular valves are closed
when pressure in atrium is higher than in ventricle;
prevents backflow of blood from ventricle to atrium
219
how to interpret if the atrioventricular valves are open
when pressure is higher in ventricle than atrium;
blood flows from ventricle to atrium
220
how to interpret if the atrioventricular valves are open
when pressure is higher in ventricle than atrium;
blood flows from ventricle to atrium
221
cardiovascular diseases
conditions affecting structures or functions of the heart e.g. chd
222
how an atheroma can result in a heart attack
atheroma causes narrowing of coronary arteries;
restricts blood flow to heart muscle supplying glucose, oxygen etc.
heart respires anaerobically, less ATP produced, not enough energy for heart to contract, lactate produced, damages heart tissue/muscle
223
risk factors of cardiovascular diseases
age, diet high in salt or saturated fat, high consumption of alcohol, stressful lifestyle, smoking cigarettes, genetics;
also high blood pressure increases damage to the artery endothelium which increases risk of atheroma which can cause blood clots
224
adaptions of the xylem
elongated cells arranged end to end to form a continuous column;
few organelles so no disruption to water flow;
end walls break down for flow;
thick cell walls with lignin-rigid so less likely to collapse under low pressure;
water proof to prevent water loss;
pits allow lateral water movements;
narrow lumen increases height water can rise due to cohesion-tension/capillary action
225
translocation
movement of solutes from source to sink
e.g. sugars made from photosynthesis in the leaves are transported to the site of respiration
226
movement of substances at the source
high conc of solute;
active transport loads solute from companion cells to sieve tubes of the phloem;
lowering the water potential inside the sieve tubes;
water enters sieve tubes by osmosis from xylem and companion cells;
increasing pressure inside sieve tubes at the source end
227
movement of substances at the sink
low conc of solute;
solutes removed to be used up;
increasing water potential inside the sieve tubes;
water leaves tubes via osmosis;
lowering pressure inside sieve tubes
228
mass flow hypothesis process
1. active transport moves sucrose from a companion cell into the sieve tube elements, reducing the water potential inside
2. osmosis moves water into the phloem, which increases the hydrostatic pressure (pressure higher near the source cell and lower near the sink)
3. solutes move down the pressure gradient, moving into the sink cells where they are converted into the molecules
4. as the solutes are removed, the water potential near the sink end increases, causing osmosis to move water out of the phloem in order to maintain hydrostatic pressure gradient between the source and the sink
229
source cells
cells that produce sugars and pump them into the phloem
230
sink cells
areas which needs the substances from the source e.g. leaves
231
what happens when sucrose reaches the sink
it is converted into starch for carbohydrate storage, which maintains the concentration gradient between the source and the sink to increase movement of sucrose into the source
232
mass flow hypothesis def
theory which states that mass flow of solutes takes place in the phloem
233
adaptions of the phloem
sieve tube elements have no nucleus and few organelles;
companion cell for each sieve tube element to carry out the living functions for the sieve cells
e.g. lots of mitochondria for ATP needed for active transport
234
how DNA is stored in eukaryotes
long, linear, associated with proteins called histones, tightly coiled into chromosomes
235
how DNA is stored in prokaryotes
short, circular, not associated with histones
236
DNA in mitochondria and chloroplasts
short, circular, not associated with histones
237
genes
sequence of DNA bases that codes for:
-amino acid sequence of a polypeptide
-a functional RNA
a gene occupies a locus (fixed position) on particular DNA molecules
238
nature of genetic code
sequence of DNA triplets (or codons) codes for a sequence of amino acids
universal: same specific DNA base triplets code for the same amino acids in all living organisms
non overlapping: discrete, each base can only be used once and in only one triplet
degenerate: the same AA can be coded for by more than one base triplet
239
genome
the complete set of genes in a cell, including those in mitochondria and/or chloroplasts
240
proteome
the full range of proteins that a cell/genome is able to produce
241
alleles
different version of the same gene
diff triplets
242
homologous pair of chromosomes
same size chromosomes with the same genes but different alleles
243
transcription
production of mRNA from DNA
occurs in the nucleus
244
translation
production of polypeptides from the sequence of codons carried by mRNA
occurs in the cytoplasm on ribosomes
245
mRNA
made by transcription;
acts as a template for translation in the cytoplasm;
sequence of bases on RNA determines sequence of AA;
straight chain molecule;
sequence of bases on RNA determined by sequence of bases on DNA;
chemically unstable so breaks down after a few days
246
tRNA
carries an amino acid (binding site);
anticodon=3 bases
anticodon bases complementary to mRNA codon;
each tRNA specific to one amino acid, in relation to its anticodon
single polynucleotide strand (3 leafed clover shape-held together by H bonds)
247
similarities between mRNA and tRNA
both single polynucleotide strand
248
differences between mRNA and tRNA
mRNA single helix/straight chained; tRNA folded into clover shape
mRNA is longer; tRNA is shorter
mRNA contains no paired bases or H bonds; tRNA has some paired bases and H bonds
249
transcription process
1.DNA double helix unwound by DNA helicase; H bonds broken
2. RNA nucleotides align next to their complementary bases on their template strand; forms temp H bonds and U replaces T
3. RNA polymerase joins adjacent nucleotides; condensation reaction; forming phosphodiester bonds
4. when RNA polymerase reaches stop codon, mRNa (prokaryotes) or pre-mRNA (eukaryotes) detaches from DNA
5. mRNA leaves nucleus via nuclear pore
250
post transcriptional modification
eukaryotic genes contain:
exons-coding
introns-non coding
pre-mRNA contains introns and exons
splicing
introns removed and exons spliced together;
spliced together in different combos for different proteins
prokaryotic DNA doesn’t contain introns;
no splicing; mRNA produced directly from DNA
251
translation
sequence of mRNA codons determines sequence of amino acids;
tRNAs carry specific amino acids, in relation to their anticodon;
at the ribosome, tRNA codon binds to mRNA codon
-tRNA anticodon complementary to mRNA codon
-H bonds formed
two AA joined by condensation, forming a peptide bond using energy from ATP;
tRNA detaches without AA and ribosome moves along mRNA to next codon
continues until stop codon where polypeptide is released
252
role of ATP in translation
hydrolysis of ATP releases energy;
for the bond between the AA and it’s corresponding tRNA molecule—AA attaches at binding site;
for peptide bond formation between amino acids
253
role of tRNA in translation
tRNA attaches to and transports a specific AA;
tRNA anticodon complementary base pairs to mRNA codon, forming H bonds;
2 tRNAs being AA tg for the formation of peptide bonds;
around 60 types of tRNA to carry 20 diff AA—genetic code is degenerate
254
role of ribosomes in translation
attaches to mRNA and houses tRNA, allowing codon-anticodon complementary base pairing;
allows peptide bonds to form between amino acids
255
gene mutation
a change in the base sequence of DNA on chromosomes;
can arise spontaneously during DNA replication (interphase);
involves base deletion/substitution
256
how can a mutation lead to the production of a non-functional protein
change in base/triplet sequence of DNA/gene;
changes sequence of codons on mRNA;
changes sequence of AA in the primary structure of the polypeptide;
changes position of H/ionic/disulphide bonds in tertiary structure of protein
257
how can a mutation lead to the production of a non-functional enzyme
change in base/triplet sequence of DNA/gene;
changes sequence of codons on mRNA;
changes sequence of AA in the primary structure of the polypeptide;
changes position of H/ionic/disulphide bonds in tertiary structure of active site;
substrate can’t bind to active site and form an ES complex
258
base deletion
one nucleotide/base removed from DNA sequence;
changes triplet/codon sequence from the point of mutation;
changes sequence of codons on mRNA after point of mutation;
changes sequence of amino acids in primary structure of polypeptide;
change position of hydrogen/ionic/disulphidr bonds in tertiary structure of protein;
change tertiary structure/shape of protein
259
base substitution
nucleotide/base in DNA replaced with another nucleotide/base; change in one base=changes one triplet;
changes one mRNA codon and one amino acid-> sequence of amino acids in primary structure of polypeptide changes
ORR
due to the genetic nature of the genetic code, the new triplet may still code for the same AA so the sequence of amino acids in the primary structure of the polypeptide remains unchanged
260
mutagenic agents
increase the rate of gene mutation
e.g. UV light or alpha particles
261
skipped meiosis
262
genetic diversity
number of different alleles of a gene in a population
263
population
group of interbreeding individuals of the same species
264
principles of natural selection
1. variation of alleles exist in population due to random DNA mutations—e.g. some bacteria contain genes for antibiotic resistance due to a mutation
2. selection pressure/change in environment—e.g. antibiotic introduced
3. those with advantageous alleles have increased chance of survival and reproduction—e.g. bacteria w gene for resistance survive and reproduce while those without it die
4. those surviving/reproducing pass on advantageous allele to offspring
5. frequency of advantageous allele increases in the population
3. happens over many generations
265
directional selection
change to environment;
selection pressure moves to one extreme or the other;
one extreme phenotype is more likely to survive and reproduce;
mean phenotype changes
266
stabilising selection
stable environment;
selection pressure acts either side of the mean;
both extremes of phenotype less likely to survive and reproduce (very small or very large babies);
mean phenotype stays the same
267
how/why does natural selection result in better adapted species
these adaptions all increase an organisms chance of survival
ANATOMICAL: structural features of an organisms body e.g. polar bears fur or whales thick layer of blubber keeps them warm
PHYSIOLOGICAL: processes inside the body e.g. brown bears hibernate in winter, lower metabolism to conserve energy so they don’t need to look for food when it’s scarce
BEHAVIOURAL: ways an organisms acts e.g. possum plays dead if they’re being threatened by a predator to escape attack
268
species
when two organisms are able to produce fertile offspring
269
courtship behaviour
allows recognition of members of the same species because courtship behaviour is species specific;
indication of sexual maturity;
stimulate release of gametes
270
phylogenetic classification system
arranges species into groups based on their evolutionary origins and relationships
hierarchical: no overlap between groups
271
genome sequencing
compare the order of base sequence of whole genome of different species
high%=more closely related
272
immunology
DNA-> mRNA -> sequence of amino acids in polypeptide;
so tertiary structure of protein tells us about sequence of DNA;
if same antibody binds to a specific antigen then it’s closely related to
273
biodiversity
the variety of living organisms in an area
274
3 types of biodiversity
species diversity
genetic diversity
ecosystem diversity
275
species diversity
the number of different species and the number of individuals of each species within a community
276
community
all of the different species in a habitat
277
local biodiversity
the variety of species living in a small habitat e.g. pond/meadow
278
global biodiversity
the variety of species living on earth
279
species richness
the number of different species in a community
280
index of diversity
describes the relationship between the number of species in a community and the number of individuals in each species
N=total number of organisms of ALL species
n=total number of organisms of each individual species
lowest possible number=1
281
why is index of diversity more useful than species richness
it measures both the number of species and the number of individuals in each species;
takes into account that some species may be present in low/high numbers
282
farming techniques that reduce biodiversity
removal of woodlands and hedgerows;
monoculture e.g. replace natural meadows with one cereal crop;
use of pesticides, herbicides and organic fertilisers;
crops better competitors for resources
283
variation
differences in characteristics between individuals within a species or between different species;
could be the result of
-genetic factors
-environmental factors
-or both
284
continuous variation
-no distinct categories;
-data tends to be quantitative;
-controlled by many genes
-strongly influenced by the environment
285
discontinuous variation
-distinct categories;
-data tends to be qualitative;
-controlled by a single/few genes;
Yeah yeah-unaffected/not strong,y influenced by the environment
286
HIV core
genetic material (RNA) and reverse transcriptase (enzyme);
needed for viral replication
287
capsid
outer protein coat
288
HIV envelope
extra outer layer, made out of the host cell’s membeane
289
protein attachments
on the exterior of the envelope to enable the virus to attach to the host’s Th cell
290
HIV replication
1. attachment proteins attach to receptors on Th cell
2. nucleic acid/ RNA enters the cell
3. reverse transcriptase converts DNA to RNA
4. viral proteins produced
5. virus particles assembled and released from cell
291
antibiotic resistance in bacteria
1. random mutations creates a resistance allele in the bacteria population
2. when exposed to the antibiotic, only those with the resistance allele will survive and reproduce
3. resistance allele frequency increases over generations
292
describe the role of antibodies in producing a positive result in an ELISA test
1. first antibody binds to antigen
2. second antibody with enzyme attached is added
3. second antibody attaches to antigen
3. substrate added and colour changes
293
describe the principles and limitations of using a TEM to investigate cell structure
PRINCIPLES:
1. electrons pass through thin specimen
2. denser parts absorb more electrons so appear darker
3. electrons have shorter wavelengths so gives higher resolution
LIMTATIONS:
1. cannot view living cells
2. complex + long preparation
3. specimen must be very thin
294
describe and explain how cell fractionation can be used to isolate mitochondria from a suspension of animal cells
1. homogenise in a blender to break down cells
2. place in an ice cold, isotonic and buffered solution
3. centrifuge at low speed to separate nuclei
4. response supernatant at higher speed to separate mitochondria in the pellet
295
name two ways in which meiosis produces genetic variation
1. crossing over
2. independent segregation
296
a mutations can lead to the production of a non-functional enzyme. explain how.
1. change in base/nucleotide sequence of DNA
2. change in amino acid sequence/primary structure
3. change in H/ionic/ disulfide bonds
4. change in tertiary structure
5. change in active site
6. substrate no longer complementary / no ES complexes formed
