Exam questions Flashcards
Describe how an unsaturated triglyceride is synthesised (3)
- one glycerol and three fatty acids
- joined by condensation reactions/ester bonds
- by enzymes
- one fatty acids is unsaturated/has CC double bond
Explain the role of collagen in the wall of the aorta (2)
- gives the wall strength
- so that the aorta doesn’t get damaged/can withstand pressure of blood
Proteases are enzymes that break down proteins
Explain how a protease breaks down elastin (3)
- active site of protease {binds to/fits} the elastin substrate
- activation energy is lowered by protease
- breaking the peptide bonds
- by hydrolysis
Describe the arrangement of phospholipids in the cell membrane in the fluid mosaic model (3)
- a phospholipid bilayer/2 layers
- polar/hydrophilic phosphate heads pointing outwards/aqueous environment
- non-polar/hydrophobic fatty acid tails pointing inwards/away from water
Describe the structure of a mRNA molecule (3)
- single stranded
- consists of ribose, phosphate and a base
- phosphodiester bonds between mononucleotides
- adenine, uracil, cytosine and guanine
Compare and contrast the structure of a triglyceride and a phospholipid (3)
similarities:
- both contain a glycerol
- both contain fatty acids
- both contain ester bonds
differences:
- triglycerides have three fatty acids whereas a phospholipid only has two
- a phospholipid contains a phosphate group whereas a triglyceride does not
Explain why the properties of LDLs enable cholesterol to be transported in the blood (3)
- {protein/phosphate heads/hydrophilic heads} are {soluble/hydrophilic/polar} and interact with blood/plasma
- fatty acids/triglycerides/cholesterol is insoluble/non-polar/hydrophobic
- therefore cholesterol is surrounded by fatty acid tails/triglycerides
Explain why an increase in temperature increases the fluidity of the membrane (2)
- because phospholipid/molecules have more kinetic energy
- because forces/interactions between fatty acid chains/phospholipids break
- therefore phospholipids can move around within the phospholipid bilayer more
State what is meant by the term osmosis (1)
- diffusion of water molecules down a water potential gradient through a semi-permeable membrane
Explain why oxygen molecules can pass directly through the cell membrane (3)
- oxygen is a small molecule
- oxygen is non-polar
- therefore can pass through gaps in the cell {membrane/hydrophobic tails}
Describe the structure of a nucleotide pair (3)
- contains deoxyribose/pentose/5 carbon sugar, phosphate and bases
- mononucleotides are held together by hydrogen bonds
- between complementary base pairs
State what is meant by the term gene (1)
- sequence of bases of DNA that codes for a polypeptide chain
Describe how the two strands of DNA forming the double helix in a gene are held together (2)
- complementary base pairing (A,T and C,G)
- enables the formation of two hydrogen bonds between adenine and thymine and three hydrogen bonds between cytosine and guanine
State what is meant by the term semi-conservative replication (2)
- increase in the number of DNA {molecules} (two new molecules are made from one molecule)
- each new molecule consists of one {parent/one original/old} strand and one new strand
Explain the importance of semi-conservative replication in the production of new cells (2)
- because it results in genetically identical daughter cells
- that will have the same structure and function as the parent cell
Describe the roles of messenger RNA (mRNA) and transfer RNA (tRNA) in protein synthesis (4)
mRNA-
- is a copy of the {code/DNA/sequence/genes}
- mRNA {moves/carries code} out of the nucleus/to the ribosomes
tRNA-
- {binds to/carries} its specific amino acid
- tRNA anticodon binds to the mRNA codon
- holds the amino acid in place until the peptide bonds have formed
Collagen is an insoluble, fibrous protein
Describe the roles of RNA in the synthesis of collagen (5)
- an mRNA molecule codes for each of the polypeptide chains in collagen
- mRNA carries a copy of the genetic code for collagen out of the nucleus to ribosome
- each tRNA molecule carries its own specific amino acid to the {ribosome/mRNA}
- anticodon on tRNA binds to the codon on the mRNA
- tRNA holds the amino acid in place whilst the peptide bonds forms
- start codon and stop codons on mRNA begin and end synthesis
Explain how the primary structure of collagen determines its properties (4)
- insoluble as there are hundreds of amino acids
- insoluble because there are many hydrophobic R groups
- strong because of the triple helix
- therefore there are many repeating amino acid sequences
- many small R groups so the triple helix can be formed
Explain why some amino acids have more than one genetic code (3)
- because it is a degenerate code
- which means there is more codes than number of amino acids
- arranging the four bases in a triplet gives 64 possible combinations and there are 20 amino acids to code for
- minimises the effect of mutations
Explain the role of the other three genetic codes (2)
- remaining codes are stop codons
- therefore no more amino acids can be added to the polypeptide chain
Explain why adding citric acid to cut fruit reduces the rate at which the fruit turns brown (2)
- active site {structure/shape} changes
- because of {acid/H+ ions} {affects hydrogen bonding/ionic bonds} of enzyme
- so substrate no longer fits (no E-S complexes formed)
Explain why a mutation might lead to a change in the activity of an enzyme (4)
- mutation results in a different sequence of amino acids
- therefore different R groups/side chains
- results in different {ionic/hydrogen/disulphide} bonds forming
- changes the shape of the active site, changing the activity of the enzyme
Describe an experiment that could be carried out to investigate the effect of enzyme concentration on the initial rate of reaction (4)
- range of different enzyme concentration (at least 5)
- idea of substrate not limiting
- reference to mixing substrate and enzyme
- description of how to measure the dependent variable with time
- description of how to measure the initial rate of reaction
- controlled variables e.g. temperature/volume/concentration of substrate
- repeat each enzyme concentration
- use a control such as distilled water for comparison
State why enzymes are described as biological catalysts (1)
- proteins which reduce the activation energy of a biological reaction
Explain why a gene mutation can result in an enzyme that is unable to break down lipids (5)
- change in the DNA base sequences
- changes the sequence of amino acids in primary structure of a {protein/enzyme}
- causes different R groups to be formed
- leading to different types of {hydrogen/ionic/disulphide} bonds
- changes folding of tertiary structure
- changes the shape of the active site
- substrate no longer fits into the enzymes active site
Suggest how the primary structure of pepsin (protein) determines its three-dimensional structure and properties (4)
- primary structure is the sequence of amino acids
- primary structure determines the position of the bonds/folding
- hydrogen/ionic/disulphide
- polar/hydrophilic R groups on the outside of the enzyme or non-polar/hydrophobic R groups on the inside of the enzyme
- pepsin is globular/soluble
- bonds determine the structure and function of the active site
- determines if the enzyme is pepsin
Describe the blood clotting process (4)
- cascade of events leading to blood clotting
- thromboplastin begins the cascade
- thromboplastin in the presence of calcium ions and vitamin K converts prothrombin into thrombin
- thromboplastin/thrombin are enzymes
- thrombin converts fibrinogen into fibrin
- fibrin forms the mesh fibres
- platelets and blood cells gets trapped in mesh creating the clot
Describe the structure of an enzyme (3)
- enzyme is a protein
- 3D/globular/tertiary structure
- held together by hydrogen/ionic/disulphide bonds
- bonds held between R groups
- ## bonds form specific active site
Define activation energy (2)
- energy needed for a reaction to occur
- by causing bonds to break
Explain why a gene mutation involving the replacement of one base with another has less effect than the loss of a base (2)
- deletion causes a whole frame shift
- replacement only changes one {codon/amino acid}
- number of amino acids stays the same with replacement
Explain why this change in the primary structure would result in the CFTR protein being non-functional (3)
- mutation causes a change in the sequence of amino acids
- therefore {hydrogen/ionic/disulphide} bonds will be different
- changes the {3D/tertiary structure}
- therefore it cannot transport chloride ions
Another mutation reduces the quantity of CFTR protein in membranes.
Explain the effects of having smaller quantities of CFTR protein in membranes (5)
- fewer chloride ions transported across the cell membrane (out of the cell)
- less regulation of the sodium ion channel
- therefore less water moves out of the cell into the mucus by osmosis
- makes mucus more viscus
- cilia cannot remove mucus
- results in blockages of airways
Explain why these removing a base and changing a base (mutations) different effects on protein structure (4)
- deletion can effect every codon (frameshift) whereas substitution will only effect one codon
- deletion likely to effect position of start/stop codons
- deletion results in a different sequence of amino acids whereas substitution may not
- substitution may code for the same amino acids
- since the genetic code is degenerate
Describe the structure of a fibrous protein (3)
- are long/contain many amino acids
- amino acid sequence is repetitive
- limited folding/no tertiary structure
- polypeptides lay parallel to each other
- bonds link chains together (cross linked)
Explain how a gene mutation causes a build up of mucus in the respiratory system of a person with cystic fibrosis (5)
- ref to CFTR protein channel
- different sequence of amino acids
- change in protein structure causes defects in CFTR protein channel
- ref to role of protein in transport of chloride ions
- ref to chloride ions not moving out of cells/not going into mucus
- ref to sodium ions moving in
- water does not move out of the cells/water moves in
- by osmosis
- mucus becomes thicker/ stickier as no water has moved out
- thick mucus cannot be moved by cilia
Explain how cystic fibrosis affects the digestive system (4)
- CFTR protein channel not functioning properly
- mucus becomes thicker/stickier
- mucus blocks {ducts}
- in the pancreas
- enzymes cannot be secreted into small intestine
- reduces digestion of food
- reduces absorbance of nutrients/energy
- weight loss/malnutrition
People with cystic fibrosis require a higher energy diet than people without cystic fibrosis. They are also more likely to develop problems in the pancreas.
Men with cystic fibrosis are less likely to be able to release sperm.
Discuss why a person with cystic fibrosis could have these symptoms (6)
- mucus is {thicker/stickier} than normal
- enzymes cannot enter small intestine because pancreatic duct is blocked with mucus
- higher energy diet is required because digestion is less effective
- pancreatic enzymes that become trapped behind mucus damage pancreatic cells such as those that produce insulin
- cysts form in pancreas
- sperm cannot leave testes because {sperm ducts/vas deferens} become blocked with mucus
- sperm ducts/vas deferens are not present therefore sperm cannot pass through
- gene mutation
- causes a non-functioning CFTR protein channel
- chloride ions cannot move out of epithelial cells
- accumulation of sodium and chloride ions in the cells {preventing water moving out of the cells into the mucus by osmosis}
Explain how gas exchange is affected in individuals with cystic fibrosis (3)
- thick/sticky mucus accumulates in the airways
- blocking/reducing airflow to alveoli
- concentration gradient of gases reduced
Describe and explain how the lungs of a mammal are adapted for rapid gas exchange (5)
- alveoli are one cell thick
- walls/endothelium of capillaries are one cell thick
- alveoli are covered by capillaries
- short diffusion distance
- large surface area provided by alveoli/capillaries
- concentration gradient is maintained by breathing
- large number of red blood cells/oxygen combines with haemoglobin
- concentration gradient of oxygen maintained by blood flow
- description of Fick’s law
