Download Chapter 2 Molecules to enzymes Short Answer

Chapter 2 Molecules to enzymes - Short answer
1a. Outline primary and quaternary protein structures.
[72 marks]
[2 marks]
Primary protein structure:
Quaternary protein structure:
Markscheme
a. (primary structure) is sequence of amino acids;
b. (quaternary structure) is the linking of two or more polypeptides to form one protein;
1b. List three limiting factors of photosynthesis.
[3 marks]
Markscheme
a. temperature;
b. pH;
c. light;
d. CO2;
2a. Define the active site of an enzyme.
[1 mark]
Markscheme
region/site where a substrate binds
2b. Explain how the active site promotes enzyme–substrate specificity.
[2 marks]
Markscheme
a. shape of active site matches that of the substrate;
b. chemical properties/charges of active site attract the substrate;
c. active site can change to induce fit of substrate;
2c.
Outline possible effects of acids on enzyme activity.
[2 marks]
Markscheme
a. changes the charge/ionization of amino acids/R-groups;
b. changes 3-D structure (of active site)/tertiary structure / denatures enzyme;
c. substrate no longer binds/fits so decreases activity;
d. could increase activity if optimum pH of enzyme is acidic;
3a.
Outline the molecular structure of different types of fatty acids.
[3 marks]
Markscheme
fatty acids share a common structure but differ in the total number of carbon atoms in the chain;
saturated fatty acids have no double bonds between carbon atoms;
unsaturated have double bond(s);
monounsaturated have one double bond / polyunsaturated have more than one double bond;
cis fatty acids have adjacent hydrogen atoms on same side of double bond and trans have them on opposite side;
(accept annotated diagrams)
3b. Evaluate the benefit of reducing cholesterol in the diet.
[3 marks]
Markscheme
cholesterol is a steroid found mainly in animal products;
it builds up in the walls of arteries / causes clogging/narrowing/blockage of artery / atherosclerosis;
lowering its ingestion may lower the probability/ risk of coronary heart disease/CHD;
cholesterol can be synthesized by the liver;
factors other than diet can affect levels of cholesterol / genetic factor more important than diet;
4a.
Other than acting as catalysts state three functions of proteins, giving an example of each.
[3 marks]
Markscheme
structural – collagen / membrane proteins;
transport – hemoglobin / protein channels;
movement – actin / myosin;
hormones – insulin / vasopressin / growth hormone;
defense – antibodies / immunoglobins;
Award any other valid function and example.
4b.
The diagram shows chemiosmosis in the mitochondrion. Label I, II and III.
[3 marks]
Markscheme
I.
ATPsynthase; (accept ATPsynthetase)
II.
\({{\text{H}}^ + }\) / protons;
III.
\({{\text{O}}_{\text{2}}}\)/oxygen;
5a. Identify the chemical group labelled I.
[1 mark]
Markscheme
phosphate
5b.
State the type of bond labelled II.
[1 mark]
Markscheme
covalent / phosphodiester
5c.
Distinguish between the sense and antisense strands of DNA during transcription.
[1 mark]
Markscheme
only the antisense strand is transcribed / the antisense strand is transcribed to mRNA and the sense strand is not
transcribed/has the same base sequence as mRNA (with uracil instead of thymine)
To award [1], reference must be made to both strands and transcription.
5d.
Compare the DNA found in prokaryotic cells and eukaryotic cells.
[2 marks]
Markscheme
Award marks for paired statements only. Answers do not need to be shown in a table format.
6a.
Glucose and galactose are examples of monosaccharides. State one other example of a monosaccharide.
[1 mark]
Markscheme
fructose/ribose/deoxyribose/ribulose/other monosaccharides apart from glucose and galactose
6b.
There are several different types of carbohydrate. State which type of carbohydrate lactose is.
[1 mark]
Markscheme
disaccharide
6c.
State the type of chemical reaction that occurs when lactose is digested into glucose and galactose.
[1 mark]
Markscheme
hydrolysis
6d.
Simple laboratory experiments show that when the enzyme lactase is mixed with lactose, the initial rate of
[2 marks]
reaction is highest at 48°C. In food processing, lactase is used at a much lower temperature, often at 5°C. Suggest reasons
for using lactase at relatively low temperatures.
Markscheme
less denaturation / enzymes last longer at lower temperatures;
lower energy costs / less energy to achieve 5° C compared to 48° C;
reduces bacterial growth / reduces (milk) spoilage;
to form products more slowly / to control rate of reaction;
7a.
List two functions of membrane proteins.
[2 marks]
Markscheme
a. hormone binding sites / receptors;
b. (immobilized) enzymes;
c. cell adhesion;
d. cell (to cell) communication;
e. passive transport/channels;
f. active transport/pumps;
g. facilitate diffusion;
h. carry electrons;
7b.
Explain why digestion of large food molecules is essential.
[1 mark]
Markscheme
a. many molecules are too large to be absorbed (by the villi) / small molecules are soluble and can be absorbed;
b. large food molecules are broken down so they can be reorganized/rearranged;
7c.
Outline why antibiotics are effective against bacteria but not against viruses.
[2 marks]
Markscheme
a. antibiotics block/inhibit specific metabolic pathways/cell functions found in bacteria;
Accept specific examples of inhibition such as cell protein synthesis, cell wall formation
b. viruses must use host/eukaryotic cell metabolism / viruses do not have their own metabolic pathways;
c. host/eukaryotic cell metabolism/pathways not blocked/inhibited by antibiotics;
7d.
Outline the use of polymerase chain reaction (PCR) to copy and amplify minute quantities of DNA.
[2 marks]
Markscheme
a. strands of DNA (fragments) split/denatured with heat;
b. complementary nucleotides added to split stands (when cooling);
c. with the use of (DNA) polymerase (and primers);
d. process/heating and cooling cycle is repeated (until enough DNA is obtained);
Accept example of PCR application e.g. paternity cases or forensic investigations.
8a.
State four elements that are needed by living organisms, other than carbon, hydrogen and oxygen, giving one
role of each.
[4 marks]
Markscheme
a. nitrogen – structure of organic molecules/proteins/nucleotides;
b. sulfur – amino acid / protein structure;
c. phosphorus – nucleic acids / energy carriers;
d. calcium – bone structure / trigger exocytosis (e.g. neurotransmitters);
e. iron – prosthetic groups / hemoglobin;
f. sodium – membrane potential;
Accept other valid roles for those elements already listed.
Accept other valid examples of elements with their roles.
To award [4 max], responses need an appropriate role for each element stated.
8b.
Outline how light energy is used and how organic molecules are made in photosynthesis.
[6 marks]
Markscheme
a. chlorophyll is the (main) photosynthetic pigment;
b. absorbs (mainly) red and blue light;
c. green light is reflected;
d. light energy absorbed is converted into chemical energy;
e. ATP produced;
f. water split;
g. to form oxygen and hydrogen;
h. ATP and hydrogen used to fix carbon dioxide to make organic molecules;
8c.
Explain the significance of complementary base pairing for replication, transcription and translation.
[8 marks]
Markscheme
a. A-T and C-G in DNA;
b. A-U and C-G in RNA;
c. complementary base pairing in replication ensures identical nucleotide sequence of new complementary strands;
d. semi-conservative replication;
e. transcription produces RNA sequence complementary to the DNA sequence (of the gene);
f. triplets of nucleotides on mRNA are codons;
g. translation converts mRNA sequence of information into a specific amino acid chain (polypeptide);
h. (each class of) tRNA carries a specific triplet of (three) bases called an anticodon;
i. anticodons bind to codons by complementary base pairing;
j. (each class of) tRNA with specific complementary anticodons carry specific amino acids;
k. sequence of mRNA codons translates into specific amino acid sequence;
l. enables conservation of information transfer from DNA to RNA to polypeptide;
9a.
Define active site.
[1 mark]
Markscheme
site on surface/portion of the enzyme/protein to which the substrate binds
9b.
Explain enzyme-substrate specificity.
[3 marks]
Markscheme
enzymes fit together with substrates similar to a lock and key;
active site has shape that gives specificity;
enzymes catalyze a reaction with a specific substrate;
example of named enzyme and its substrate;
substrate held precisely in (optimum) position to make/break bonds/carry out reaction / chemical interaction occurs
between enzyme and substrate;
Accept these points shown in an annotated drawing.
10a.
State two functions of proteins, giving a named example of each.
[2 marks]
Markscheme
enzymes/biological catalyst – amylase/protease/lipase/catalase;
defence/immunity – immunoglobin/antibody;
structure – collagen;
movement – actin/myosin;
transport – hemoglobin;
synthesis – ligase/DNA polymerase;
hormonal communication – insulin/luteinizing hormone; MUST be proteinaceous
food stores – casein in milk;
pigments – opsin;
Accept any other valid responses.
10b.
Explain the significance of polar and non-polar amino acids.
[3 marks]
Markscheme
polar amino acids have hydrophilic R groups, non-polar have hydrophobic R groups;
non-polar amino acids in centre of water-soluble proteins stabilise their structure;
non-polar amino acids cause proteins to remain embedded in membrane;
polar amino acids on surface of proteins make them water-soluble;
polar amino acids create hydrophilic channels/protein pores in membranes;
enzyme active site specificity depends on amino acids present/polar and nonpolar amino acids can play a role in
substrate interactions at the active site;
11a.
State the type of bonds that
[2 marks]
(i) connect base pairs in a DNA molecule.
(ii) link DNA nucleotides into a single strand.
Markscheme
(i) hydrogen
(ii) covalent / phosphodiester linkage
11b.
Distinguish between DNA and RNA nucleotides by giving two differences in the chemical structure of the
molecules.
[2 marks]
Markscheme
DNA has deoxyribose, RNA has ribose;
DNA has base T/thymine, RNA has base U/uracil;
Do not accept double or single strands as chemical structure.
11c.
Explain the role of transfer RNA (tRNA) in the process of translation.
[2 marks]
Markscheme
tRNA attaches to (specific) amino acid;
tRNA (with amino acid) moves to the ribosome;
anticodon of tRNA binds with codon of mRNA;
© International Baccalaureate Organization 2017
International Baccalaureate® - Baccalauréat International® - Bachillerato Internacional®
Printed for Highland High School