B1 exam qs Flashcards
describe how ATP is formed from its component molecules
adenine ribose and 3 phosphates
condensation reaction
ATP synthase
compare and contrast the properties of triglycerides and phospholipids
- both contain ester bonds between glycerol and fatty acid
- both contain glycerol
- both are insoluble
- both contain C H O, phospholipids contain P
- triglyceride has 3 fatty acids, phospholipids contain 2
- fatty acids on both may be saturated or unsaturated
- triglycerides are hydrophobic, phospholipds have hydrophobic and hydrophilic regions
- phospholipds form bilayer in water, triglycerides dont
state and explain the property of water that can help to buffer changes in temperature
high specific heat capacity
requires a lot of heat to change temp
describe a biochemical test to show that raffinose contains a non reducing sugar
heat with acid and neutralise
heat with benedicts
red precipitate
Describe the biochemical tests you would use to confirm the presence of lipid,
non-reducing sugar and amylase in a sample.
lipid = add ethanol, then water, shake - white milky emulsion
non-reducing sugar = do benedicts test, if negative, boil with acid, add HCl, heat with benedicts - red precipitate
amylase = add biuret - purple
add starch - test for reducing sugar
describe the role of iron ions, sodium ions and phosphate ions in cells
Iron ions
1. Haemoglobin transports oxygen;
Sodium ions
2. aids Co-transport of glucose(into cells);
3. sodium moved out by active transport/Na - K pump;
4. Creates a sodium concentration gradient;
Phosphate ions
- Joins nucleotides
- Used to produce ATP
- Phosphorylates other compounds making them more reactive;
- Hydrophilic/water soluble part of phospholipid bilayer/membrane
the movement of substances across cell membranes is affected by membrane structure
describe how
- Phospholipid bilayer allows diffusion of non-polar, lipid-soluble substances
- Phospholipid bilayer prevents diffusion of charged, lipid-insoluble substances
- Carrier proteins allow active transport;
- Channel and carrier proteins allow facilitated diffusion and co-transport
- Shape or charge of channel or carrier determines which substances move
-
Number of channels or carriers determines how much movement;
7.Membrane surface area determines how much diffusion; - Cholesterol affects fluidity/rigidity/permeability;
explain 6 properties that make water important for organisms
- metabolite in photosynthesis/respiration
- solvent- allows transport of substances
- high specific heat capacity - buffers changes in temp
- large latent heat of vapourisation - provides cooling effect
- cohesion - supports molecules of water
- cohesion - provides surface tension for small organisms
describe the chemical reactions involved in the conversion of polymers to monomers and monomers to polymers
- A condensation reaction joins monomers together and forms a (chemical) bond and releases water;
- A hydrolysis reaction breaks a (chemical) bond between monomers and uses water;
- alpha glucose - starch/glycogen
- beta glucose - cellulose
- e.g DNA or RNA , nucleotide and polynucleotide
describe the process of semi conservative replication of DNA
- DNA helicase unwinds DNA, breaks hydrogen bonds;
- Both strands act as templates;
- (Free DNA) nucleotides line up in complementary pairs
- DNA polymerase joins nucleotides (of new strand);
- Forming phosphodiester bonds;
- Each new DNA molecule consists of one
old strand and one new strand;
Following digestion and absorption of food, the undigested remains are processed to form
faeces in the parts of the intestine below the ileum.
The faeces of people with constipation are dry and hard. Constipation can be treated by
drinking lactulose. Lactulose is soluble, but is not digested or absorbed in the human
intestine.
Use your knowledge of water potential to suggest why lactulose can be used to help people
suffering from constipation.
- (Lactulose) lowers the water potential of faeces
- Water enters by osmosis softens the faeces
Glycogen and cellulose are both carbohydrates.
Describe two differences between the structure of a cellulose molecule and a glycogen
molecule.
- Cellulose is made up of β-glucose (monomers)
- glycogen is made up of α-glucose
- Cellulose molecule is a straight chain
- glycogen is branched
- Cellulose molecule is straight chain
- glycogen is coiled
- glycogen has 1,4 and 1,6 glycosidic bonds
- cellulose has only 1,4- glycosidic bonds
Describe and explain two features of starch that make it a good storage molecule.
- Insoluble, so doesn’t affect water potential;
- Branched / coiled , so makes molecule compact
Describe the structure of glycogen
- polymer of a-glucose
- joined by glycosidic bonds
Suggest how glycogen acts as a source of energy.
- Hydrolysed (to glucose);
- Glucose used in respiration
Suggest and explain two ways the cell-surface membranes of the cells lining the uterus
may be adapted to allow rapid transport of nutrients.
- folded membrane increases SA
- large number of carrier proteins for active transport
Explain one way in which starch molecules are adapted for their function in plant cells.
- Insoluble;
- Don’t affect water potential
Explain how cellulose molecules are adapted for their function in plant cells
- Long and straight chains;
- Become linked together by many hydrogen bonds to form fibrils;
- Provide strength (to cell wall).
Suggest why the water potential of apple juice decreases when apples are stored.
- Starch hydrolysis (to maltose);
- Maltose is soluble, but starch is insoluble;
Cotton is a plant fibre used to make cloth. Explain how cellulose gives cotton its strength.
(long) straight / unbranched chains;
(idea of more than 1) chains form (micro)fibrils;
H bonds holding chains together
Describe how you would test for the presence of a lipid in a liquid sample of food.
Add ethanol/alcohol then add water and shake/mix
2. white emulsion
Give one similarity and two differences between the membrane structure shown in Figure
2 and the fluid-mosaic model of membrane structure.
- Both have a phospholipid bilayer
- No channel/carrier proteins, whereas fluid mosaic does
Describe how a triglyceride molecule is formed
- One glycerol and three fatty acids;
- Condensation (reactions) and removal of three molecules of water;
- Ester bond(s) (formed);
It is known that:
* during respiration saturated fatty acids yield more energy than unsaturated fatty acids
* saturated fatty acids have higher melting points than unsaturated fatty acids
* lipases in seeds act more rapidly on liquid substrates.
Use this information and Table 2 to show how each population is better adapted for its
natural environment when compared with the other population.
- Population 1 grew longer roots in warm temperatures and population 2
grew longer roots in cool temperatures; - Standard deviations do not overlap so difference (in mean) unlikely to
be/not due to chance; - Population 1 (is better adapted to warm conditions because it) has more
saturated fatty acids so more energy available (and more growth); - Population 2 (is better adapted to cool conditions because it) has more
unsaturated/liquid fatty acids so more lipase activity (and more growth);
name the bond between a glycerol and fatty acid
ester
This fat substitute cannot be digested in the gut by lipase.
Suggest why.
not complementary;
Unable to fit/bind to (active site of) lipase
Describe how you could use the emulsion test to show that a
seed contains lipids.
- Crush / grind;
- With ethanol / alcohol;
- Then add water / then add to water;
- Forms emulsion / goes white / cloudy;
Use the information in the figure to explain two ways in which fatty acids are important in the
formation of new cells.
Fatty acids used to make phospholipids;
Phospholipids in membranes;
More phospholipids more membranes made;
Fatty acids respired to release energy;
More triglycerides more energy released;
Energy used for cell production / production of named cell component
Describe the induced-fit model of enzyme action and how an enzyme acts as a catalyst
- Substrate binds to the active site
- Active site changes shape so it is complementary to substrate
- reduces activation energy
A competitive inhibitor decreases the rate of an enzyme-controlled reactio
- Inhibitor similar shape to substrate;
- Fits/binds to active site;
- Prevents/reduces enzyme-substrate complex forming;
suggest how eating stale bread could help to reduce
weight gain.
- Less hydrolysis of starch;
- (To) maltose;
- (So) less absorption (of glucose)
Explain how the active site of an enzyme causes a high rate of reaction.
1. Lowers activation energy;
2. Induced fit causes active site to change shape;
3. enzyme-substrate complex causes bonds to form/break
Formation of an enzyme-substrate complex increases the rate of reaction.
- Reduces activation energy;
- Due to bending bonds
A decrease in temperature decreases the kinetic energy of molecules in a solution. Explain
how a decrease in temperature decreases the rate of an enzyme-controlled reaction.
molecules moving less / slower; reduces chance of collision
Urea breaks hydrogen bonds. Explain how the addition of urea would affect the rate of an
enzyme-controlled reaction.
these bonds maintain tertiary structure (of enzyme);
(shape of) active site changes;
substrate no longer fits / enzyme-substrate complex not formed
Humans and grasshoppers have very similar percentages of each base in their DNA
but they are very different organisms.
Use your knowledge of DNA structure and function to explain how this is possible
- Have different genes;
- a different sequence
- so different amino acid
Use the figure in part (a) and your knowledge of enzyme action and DNA replication to
explain why new nucleotides can only be added in a 5’ to 3’ direction.
- Reference to DNA polymerase;
- (Which is) specific;
- Only complementary with / binds to 5’ end (of strand);
- Shapes of 5’ end and 3’ end are different
Use Figure 1, Figure 2 and your knowledge of enzyme action to explain why the arrows
point in opposite directions.
- ) DNA has antiparallel strands / described;
- (Figure 1 shows) shape of the nucleotides is different / nucleotides aligned
differently; - Enzymes have active sites with specific shape;
- Only substrates with complementary shape can bind with
active site of enzyme
Contrast the structures of ATP and a nucleotide found in DNA to give two differences.
- ATP has ribose and DNA nucleotide has deoxyribose;
- ATP has 3 phosphate (groups) and DNA nucleotide has 1
phosphate (group); - ATP – base always adenine and in DNA nucleotide base can
be different / varies;
The enzymes DNA helicase and DNA polymerase are involved in DNA replication.
Describe the function of each of these enzymes.
- DNA helicase – (unwinding DNA and) breaking hydrogen
bonds - DNA polymerase – joins (adjacent) nucleotides
name the bond between phosphate and pentose sugar / between two nucleotides
phosphodiester
Use your knowledge of semi-conservative replication of DNA to suggest:
1. the role of the single-stranded DNA fragments
2. the role of the DNA nucleotides.
Role of single-stranded DNA fragments
1. Template;
2. Determines order of nucleotides/bases;
Role of DNA nucleotides
3. Forms complementary pairs / A – T, G - C
Name the protein associated with DNA in a chromosome.
histone
Describe how a phosphodiester bond is formed between two nucleotides within a DNA
molecule.
- Condensation
- (Between) phosphate and deoxyribose;
- (Catalysed by) DNA polymerase;
Describe how an ATP molecule is formed from its component molecules.
- adenine, 3 phosphates, ribose
- condensation reaction
- ATP synthase
State and explain the property of water that can help to buffer changes in temperature
- high specific heat capacity
- requires a lot of energy to change temp
Water and inorganic ions have important biological functions within cells.
(a) Give two properties of water that are important in the cytoplasm of cells.
- Polar molecule;
- Acts as a (universal) solvent;
- Reactive;
- Takes place in hydrolysis/condensation
Compare and contrast the processes by which water and inorganic ions enter cells
- Comparison: both move down concentration gradient;
- Comparison: both move through (protein) channels in membrane;
- Contrast: ions can move against a concentration gradient by active transport
describe the structure of proteins
- polymer of amino acids
- joined by peptide bonds
- forms by condesation
- primary structure is the sequence of amino acids
- secondary structure us folding due to hydrogen bonding to a-glucose and b-pleated sheets
- tertiary structure 3D folding due to hydrogen bonding/ionic/disulphide bonds
- Quaternary structure is two or more polypeptide chains
describe 5 uses for ATP in orgsnisms
metabolic processes
muscle contraction for movement
active transport to move ions against conc. gradient
secretion where lysosomes are made to aid movement of products out of cell
activation of molecules - phosporylation ny addition of Pi makes molecules more reactive
describe how the structure of DNA is related for its functions
- sugar phosphate backbone - provides strength
- long molecule - store lots of info
- helix - compact
- base sequence codes for amino acids
- double stranded- accurate replication can occur semi conservatively
- weak hydrogen bonds - for replication
- many hydrogen bonds so stable and strong
describe competitive and non competitive inhibition of enzymes
- inhibitors prevent ES complexes forming
- competitive inhibitor is similar shape to substrate
- binds to active site
- overcome by having more substrates
- non-competitive inhibitors bind to allosteric site on enzyme
- changes shape of active site
- cant be overcome by adding more substrate
Give three properties of water that are important in biology
- metabolite
- solvent
- high heat capacity
*large latent heat of vaporisation - cohesion
describe DNA replication
DNA helicase breaks hydrogen bonds between bases
unwinds the helix separating the two strands
new strands formed on each of the two single strands;
nucleotides added to form new strands;
complementary base pairing;
A to T and G to C;
DNA polymerase forms the new complementary strands;
replication is semi-conservative;
each of the DNA molecules formed has one old and one new strand
