Topic 3

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Multiple Choice Questions

Which statement about water is correct? A. The atoms within a molecule of water are held together by hydrogen bonds. B. Water has a low heat capacity allowing enzymatic reactions to happen at a wide range of temperatures. C. Water molecules are polar, therefore fatty acids do not dissolve. D. Ice has a higher density than liquid water, therefore some organisms can live under the ice.

Which diagram best illustrates the interactions between water molecules?

Which of the following is an organic compound made by all plants? A. Carbon dioxide B. DNA C. Lactose D. Oxygen

Which type of molecule is shown in the diagram below? A. Peptide B. Carbohydrate C. Lipid D. Nucleic acid

How many molecules of water are required to completely hydrolyse a polypeptide made up of 23 amino acids? A. 11 B. 22 C. 23 D. 44

What chemical reaction is taking place when a dipeptide becomes two amino acids? A. Condensation B. Hydrolysis C. Denaturation D. Polymerization

What is denaturation? A. A structural change of a protein that results in the loss of its biological properties B. A change in the genetic code of an organism C. A change in the amino acid sequence of a protein causing a disruption of its 3D shape D. The process by which amino acids are broken down and ammonia is released

The percentage of thymine in the DNA of an organism is approximately 30%. What is the percentage of guanine? A. 70% B. 30% C. 40% D. 20%

What is replicated by a semi-conservative process? A. Messenger RNA (mRNA) only B. Messenger RNA (mRNA) and transfer RNA (tRNA) only C. Messenger RNA (mRNA), transfer RNA (tRNA) and DNA only D. DNA only

What principle is necessary to preserve the sequence of DNA during replication? A. Base pairing is complementary. B. One gene codes for one polypeptide. C. Substrates are specific to enzymes. D. The genetic code is universal.

Which enzyme catalyzes the elongation of the leading strand? A. RNA polymerase B. Helicase C. DNA polymerase D. Ligase

In some people, hemoglobin always contains the amino acid valine in place of a glutamic acid at one position in the protein. What is the cause of this? A. An error in transcription of the hemoglobin gene B. An error in translation of the mRNA C. Lack of glutamic acid in the diet D. A base substitution in the hemoglobin gene

What does the universal nature of the genetic code allow? A. Change of genetic code in the same species B. Transfer of genes between species C. Formation of clones D. Infection by bacteria

What is a codon? A. A sequence of nucleotides on rRNA that corresponds to an amino acid B. A sequence of nucleotides on mRNA that corresponds to an amino acid C. A sequence of nucleotides on tRNA that corresponds to an amino acid D. A sequence of nucleotides on DNA that corresponds to an amino acid

If mRNA has a codon CAU, what is the corresponding anticodon on the tRNA molecule? A. CAT B. GUA C. CAU D. GTA

ANSWERS

Which statement about water is correct? A. The atoms within a molecule of water are held together by hydrogen bonds. B. Water has a low heat capacity allowing enzymatic reactions to happen at a wide range of temperatures. C. Water molecules are polar, therefore fatty acids do not dissolve. D. Ice has a higher density than liquid water, therefore some organisms can live under the ice.

Which statement about water is correct? A. The atoms within a molecule of water are held together by hydrogen bonds. B. Water has a low heat capacity allowing enzymatic reactions to happen at a wide range of temperatures. C. Water molecules are polar, therefore fatty acids do not dissolve. D. Ice has a higher density than liquid water, therefore some organisms can live under the ice.

Which diagram best illustrates the interactions between water molecules?

Which diagram best illustrates the interactions between water molecules? B

Which of the following is an organic compound made by all plants? A. Carbon dioxide B. DNA C. Lactose D. Oxygen

Which of the following is an organic compound made by all plants? A. Carbon dioxide B. DNA C. Lactose D. Oxygen

Which type of molecule is shown in the diagram below? A. Peptide B. Carbohydrate C. Lipid D. Nucleic acid

Which type of molecule is shown in the diagram below? A. Peptide B. Carbohydrate C. Lipid D. Nucleic acid

How many molecules of water are required to completely hydrolyse a polypeptide made up of 23 amino acids? A. 11 B. 22 C. 23 D. 44

How many molecules of water are required to completely hydrolyse a polypeptide made up of 23 amino acids? A. 11 B. 22 C. 23 D. 44

What chemical reaction is taking place when a dipeptide becomes two amino acids? A. Condensation B. Hydrolysis C. Denaturation D. Polymerization

What chemical reaction is taking place when a dipeptide becomes two amino acids? A. Condensation B. Hydrolysis C. Denaturation D. Polymerization

What is denaturation? A. A structural change of a protein that results in the loss of its biological properties B. A change in the genetic code of an organism C. A change in the amino acid sequence of a protein causing a disruption of its 3D shape D. The process by which amino acids are broken down and ammonia is released

What is denaturation? A. A structural change of a protein that results in the loss of its biological properties B. A change in the genetic code of an organism C. A change in the amino acid sequence of a protein causing a disruption of its 3D shape D. The process by which amino acids are broken down and ammonia is released

The percentage of thymine in the DNA of an organism is approximately 30%. What is the percentage of guanine? A. 70% B. 30% C. 40% D. 20%

The percentage of thymine in the DNA of an organism is approximately 30%. What is the percentage of guanine? A. 70% B. 30% C. 40% D. 20%

What is replicated by a semi-conservative process? A. Messenger RNA (mRNA) only B. Messenger RNA (mRNA) and transfer RNA (tRNA) only C. Messenger RNA (mRNA), transfer RNA (tRNA) and DNA only D. DNA only

What is replicated by a semi-conservative process? A. Messenger RNA (mRNA) only B. Messenger RNA (mRNA) and transfer RNA (tRNA) only C. Messenger RNA (mRNA), transfer RNA (tRNA) and DNA only D. DNA only

What principle is necessary to preserve the sequence of DNA during replication? A. Base pairing is complementary. B. One gene codes for one polypeptide. C. Substrates are specific to enzymes. D. The genetic code is universal.

What principle is necessary to preserve the sequence of DNA during replication? A. Base pairing is complementary. B. One gene codes for one polypeptide. C. Substrates are specific to enzymes. D. The genetic code is universal.

Which enzyme catalyzes the elongation of the leading strand? A. RNA polymerase B. Helicase C. DNA polymerase D. Ligase

Which enzyme catalyzes the elongation of the leading strand? A. RNA polymerase B. Helicase C. DNA polymerase D. Ligase

In some people, hemoglobin always contains the amino acid valine in place of a glutamic acid at one position in the protein. What is the cause of this? A. An error in transcription of the hemoglobin gene B. An error in translation of the mRNA C. Lack of glutamic acid in the diet D. A base substitution in the hemoglobin gene

In some people, hemoglobin always contains the amino acid valine in place of a glutamic acid at one position in the protein. What is the cause of this? A. An error in transcription of the hemoglobin gene B. An error in translation of the mRNA C. Lack of glutamic acid in the diet D. A base substitution in the hemoglobin gene

What does the universal nature of the genetic code allow? A. Change of genetic code in the same species B. Transfer of genes between species C. Formation of clones D. Infection by bacteria

What does the universal nature of the genetic code allow? A. Change of genetic code in the same species B. Transfer of genes between species C. Formation of clones D. Infection by bacteria

What is a codon? A. A sequence of nucleotides on rRNA that corresponds to an amino acid B. A sequence of nucleotides on mRNA that corresponds to an amino acid C. A sequence of nucleotides on tRNA that corresponds to an amino acid D. A sequence of nucleotides on DNA that corresponds to an amino acid

What is a codon? A. A sequence of nucleotides on rRNA that corresponds to an amino acid B. A sequence of nucleotides on mRNA that corresponds to an amino acid C. A sequence of nucleotides on tRNA that corresponds to an amino acid D. A sequence of nucleotides on DNA that corresponds to an amino acid

If mRNA has a codon CAU, what is the corresponding anticodon on the tRNA molecule? A. CAT B. GUA C. CAU D. GTA

If mRNA has a codon CAU, what is the corresponding anticodon on the tRNA molecule? A. CAT B. GUA C. CAU D. GTA

Which of the following is the best definition of cell respiration? A. A process needed to use energy, in the form of ATP, to produce organic compounds B. A process used to provide oxygen to the atmosphere C. A controlled release of energy, in the form of ATP, from organic compounds in cells D. A controlled release of energy in the production of food from organic compounds

Which of the following is the best definition of cell respiration? A. A process needed to use energy, in the form of ATP, to produce organic compounds B. A process used to provide oxygen to the atmosphere C. A controlled release of energy, in the form of ATP, from organic compounds in cells D. A controlled release of energy in the production of food from organic compounds

What happens during the pathway of glycolysis? A. Glucose is broken down into pyruvate. B. Carbon dioxide is produced. C. More ATP is consumed than is produced. D. Lactic acid is produced.

What happens during the pathway of glycolysis? A. Glucose is broken down into pyruvate. B. Carbon dioxide is produced. C. More ATP is consumed than is produced. D. Lactic acid is produced.

What is the source of the oxygen released into the air as a product of photosynthesis? A. Chlorophyll B. Carbon dioxide only C. Water only D. Both water and carbon dioxide

What is the source of the oxygen released into the air as a product of photosynthesis? A. Chlorophyll B. Carbon dioxide only C. Water only D. Both water and carbon dioxide

How can the rate of photosynthesis of a plant be directly measured? A. By measuring the rate of oxygen produced B. By measuring the rate of carbon dioxide produced C. By measuring the rate of plant growth D. By measuring the rate of light absorbed

How can the rate of photosynthesis of a plant be directly measured? A. By measuring the rate of oxygen produced B. By measuring the rate of carbon dioxide produced C. By measuring the rate of plant growth D. By measuring the rate of light absorbed

Which two colours of light does chlorophyll absorb most? A. Red and yellow B. Green and blue C. Red and green D. Red and blue

Which two colours of light does chlorophyll absorb most? A. Red and yellow B. Green and blue C. Red and green D. Red and blue

Essay questions

Explain how the properties of water are significant to living organisms. [9] THINK: Cohesive, Thermal, Solvent water is transparent / light passes through water; this allows organisms to live below the surface / plants to photosynthesize; hydrogen bonds between water molecules make water cohesive; this gives water a high surface tension allowing animals to live on the surface / maintains lung structure (pleural membranes); helps in water movement through plants/transpiration; water has a high latent heat of vaporization / OWTTE; evaporation/sweating/transpiration leads to cooling; water has a high specific heat capacity / OWTTE; this provides a stable environment for water organisms; ice is less dense than water / water has a maximum density at 4°C; surface (pond/lake/ocean) freezes first, allowing organisms to survive in the water below; water is a universal solvent; can transport materials around organisms/plants/animals; can be a solvent for chemical reactions in organisms;

Compare the use of carbohydrates and lipids in energy storage Compare the use of carbohydrates and lipids in energy storage. [4] USE TABLES

Compare the use of carbohydrates and lipids in energy storage. [4] both lipids and carbohydrates are primary sources of energy for organisms; lipids store more energy per unit mass/per gram than carbohydrates /lipids generally provide 2 to 3 times the energy of carbohydrates for a given mass; lipids provide 38 kJ g–1/9 C g–1 whereas carbohydrates have 17 kJ g–1/4 C g–1; carbohydrates are easier to transport (than lipids) making their energy more accessible; because lipids are insoluble (in water) whereas (small) carbohydrates are soluble (in water); carbohydrates are more easily taken out of storage making their energy more quickly available; carbohydrates are short-term storage molecules, whereas lipids provide long-term storage;

The big picture: from gene to protein mRNA Protein

Explain how the base sequence of DNA is conserved during replication

3.4.1 How does DNA replication work? Unwinding the double helix helicase controls unwinding of coiled DNA Separation of the strands by helicase helicase separates complementary strands of DNA, producing a replication fork single strand binding proteins keep the two strands of DNA separate Formation of new complementary strands by DNA polymerase DNA polymerase uses a single parent strand of DNA as a template, adding free nucleotides from solution to the parent/template strand according to the complementary base pairing rules (A=T, G=C)

Explain how the base sequence of DNA is conserved during replication DNA replication is semi-conservative; DNA is split into two single/template strands; nucleotides are assembled on/attached to each single/template strand; by complementary base pairing; adenine with thymine and cytosine with guanine / A with T and C with G; strand newly formed on each template strand is identical to other template strand; DNA polymerase used;

Explain the process of transcription leading to the formation of mRNA

3.5.2 DNA transcription A. Initiation: RNA polymerase is an enzyme complex which: unwinds and unzips DNA double strand attaches to promoter region of gene, which marks the beginning point for transcription B. Elongation: RNA polymerase: uses DNA strand as a template synthesizes a complementary RNA strand using base pairing rules A = U, T = A, G = C, C = G C. Termination: RNA polymerase : reaches termination region of the gene, which marks the end of the coding sequence terminates transcription by releasing both DNA and RNA

3.5.2 Transcription

HL: Explain the process of transcription leading to the formation of mRNA. [8] RNA polymerase; (polymerase number is not required) binds to a promoter on the DNA; unwinding the DNA strands; binding nucleoside triphosphates; to the antisense strand of DNA; as it moves along in a 5′→3′ direction; using complementary pairing/A-U and C-G; losing two phosphates to gain the required energy; until a terminator signal is reached (in prokaryotes); RNA detaches from the template and DNA rewinds; RNA polymerase detaches from the DNA; many RNA polymerases can follow each other; introns have to be removed in eukaryotes to form mature mRNA; 8 max

Major players mRNA (codon = group of 3 nucelotide bases) Large subunit ribosome (A site and P site) Small subunit ribosome tRNA (anticodon) Amino acid attached to tRNA

3.5.4 1.Initiation mRNA binds to the small subunit of the ribosome AUG is universal start codon. tRNA with anticodon UAC and carrying AA methionine enters the P-site during translation tRNA anticodon binds to mRNA codon by complementary base pairing large ribosomal subunit binds and produces two binding sites: P site and A site

3.5.4 2. Elongation tRNA with anticodon complementary to second mRNA codon binds to A site, with appropriate amino acid attached to tRNA Enzymes in ribosome catalyze formation of peptide bond between P site A site amino acids to create a polypeptide P site tRNA is separated from amino acid and exits ribosome Ribosome moves one codon along the mRNA, thus shifting previous A-site tRNA to P-site, and opening A-sites

3.5.4 3. Termination When ribosomal A-site reaches a stop codon, no tRNA has a complementary anticodon. Release factor protein binds to A-site stop codon. Release: polypeptide, mRNA. Separate large and small ribosomal subunits

Translation occurs in living cells Translation occurs in living cells. Explain how translation is carried out, from the initiation stage onwards. [9 marks] translation involves initiation, elongation/translocation and termination; mRNA binds to the small sub-unit of the ribosome; ribosome slides along mRNA to the start codon; anticodon of tRNA pairs with codon on mRNA: complementary base pairing (between codon and anticodon); (anticodon of) tRNA with methionine pairs with start codon / AUG is the start codon; second tRNA pairs with next codon; peptide bond forms between amino acids; ribosome moves along the mRNA by one codon; movement in 5′ to 3′ direction; tRNA that has lost its amino acid detaches; another tRNA pairs with the next codon/moves into A site; tRNA activating enzymes; link amino acids to specific tRNA; stop codon (eventually) reached;

Compare how pyruvate is used in human cells when oxygen is available and when oxygen is not available. [5] aerobic cell respiration if oxygen available and anaerobic if unavailable; pyruvate enters mitochondrion for aerobic respiration; whereas pyruvate stays in the cytoplasm for processing under anaerobic conditions; pyruvate converted aerobically into carbon dioxide and water; whereas pyruvate converted anaerobically to lactate; large ATP yield when oxygen available/from aerobic cell respiration; no (further) ATP yield without oxygen;

What is photosynthesis? Conversion of light energy into chemical energy Chlorophyll is the main photosynthetic pigment

So how does photosynthesis work? Light dependent reaction Energy absorbed by chlorophyll is used to produce ATP Photolysis of water: Energy absorbed by chlorophyll is used to split water molecules Forms oxygen and hydrogen

So how does photosynthesis work? Light independent reaction Carbon dioxide absorbed for use in photosynthesis Inorganic carbon dioxide molecules to organic form via fixation Use hydrogen (from photolysis) and ATP

green light is reflected; Outline how light energy is used and how organic molecules are made in photosynthesis. [6] chlorophyll is the (main) photosynthetic pigment; absorbs (mainly) red and blue light; green light is reflected; light energy absorbed is converted into chemical energy; ATP produced; water split; to form oxygen and hydrogen; ATP and hydrogen used to fix carbon dioxide to make organic molecules; 6 max

Explain methods that can be used to measure the rate of photosynthesis measure production of oxygen; because oxygen is a by-product of photosynthesis; example of technique for measuring oxygen production (count bubbles/use sensors/other); measure uptake of carbon dioxide; because carbon dioxide is used during photosynthesis; example of technique for measuring carbon dioxide production (sensor, aquatic pH shift); measure biomass of (batches of) plants; increase in biomass gives (indirect) measure of rate of photosynthesis; Since the command term is explain, reasons must be given to receive full marks. 5 max