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Biology Exam Questions > 4 Genetic information, variation and relationships between organisms EQs > Flashcards

4 Genetic information, variation and relationships between organisms EQs Flashcards

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1
Q

Give the two types of molecule from which a ribosome is made (2 marks)

A

RNA and Protein

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2
Q

Describe the role of tRNA in the process of translation (3 marks)

A
  1. Anticodon complementary to codon
  2. specific amino acid transferred to ribosome,
  3. correct sequence of amino acids polypeptide
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3
Q

Describe the role of a ribosome in the production of a polypeptide (3 marks)

A
  1. mRNA binds to ribosome,
  2. tRNA with complementary anticodon forms base pairs with the mRNA codon as there are two binding sites
  3. peptide bond forms between amino acids via condensation reaction
  4. moves along to next codon
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4
Q

Give two differences between structure of mRNA and tRNA (2 marks)

A
  1. mRNA does not have hydrogen bonds, tRNA does
  2. mRNA is linear, tRNA is cloverleaf
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5
Q

What is the proteome of a cell? (1 mark)

A

Range of different proteins that a cell is able to produce

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6
Q

Describe how a phosphodiester bond is formed between two nucleotides within a DNA
molecule. (2 marks)

A
  1. Condensation reaction
  2. Between phosphate and deoxyribose
  3. Catalysed by DNA polymerase
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7
Q

Name the protein associated with DNA in a chromosome. (1 mark)

A

Histone

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8
Q

The nucleus and a chloroplast of a plant cell both contain DNA.
Give three ways in which the DNA in a chloroplast is different from DNA in the nucleus (3 marks)

A

In chloroplasts:
1.   DNA shorter
3.   DNA circular not linear
4.   Not associated with histones, unlike nuclear DNA

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9
Q

Not all mutations in the nucleotide sequence of a gene cause a change in the structure of a polypeptide.
Give two reasons why. (2 marks)

A
  1. Triplets code for same amino acid
  2. Occurs in introns
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10
Q

DNA is a polymer of nucleotides. Each nucleotide contains an organic base.
Explain how the organic bases help to stabilise the structure of DNA. (2 marks)

A
  1. Hydrogen bonds between the base pairs holds two strands together
  2. Many hydrogen bonds provides strength
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11
Q

Suggest one advantage of showing the genetic code as base sequences on mRNA, rather than triplets on DNA. (1 mark)

A

Because ribosomes assemble polypeptides using mRNA code

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12
Q

What name is given to a group of three bases on mRNA that codes for an amino acid? (1 mark)

A

Codon

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13
Q

Suggest the role of the mRNA base triplets UGA, UAG and UAA. (2 marks)

A
  1. Stop translation;
  2. Result in detachment of polypeptide chain from ribosome.
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14
Q

Describe two differences between the structure of a tRNA molecule and the structure of an
mRNA molecule (2 marks)

A
  1. tRNA is ‘clover leaf shape’, mRNA is linear;
  2. tRNA has hydrogen bonds, mRNA does not;
  3. tRNA has an amino acid binding site, mRNA does not;
  4. tRNA has anticodon, mRNA has codon;
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15
Q

In a eukaryotic cell, the structure of the mRNA used in translation is different from the
structure of the pre-mRNA produced by transcription.
Describe and explain a difference in the structure of these mRNA molecules. (2 marks)

A
  1. mRNA has no introns
  2. because of splicing
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16
Q

Why is the genetic code described as being universal? (1 mark)

A

In all organisms the same triplet codes for the same amino acid

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17
Q

A scientist investigated possible relationship between air
pollution and the size of seeds produced by one species of tree.
He was provided with a very large number of seeds collected from a population of
trees in the centre of a city and also a very large number of seeds collected from a
population of trees in the countryside.
Describe how he should collect and process data from these seeds to investigate
whether there is a difference in seed size between these two populations of trees.
[5 marks]

A
  1. Use random sample of seeds from each population
  2. Use large enough sample to be representative of whole population;
  3. Measure the mass
  4. Calculate a mean and standard deviation for each population
  5. Use the (Student’s) t-test;
  6. Analyse whether there is a significant difference
    between the means of the two populations;
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18
Q

Describe how a gene is a code for the production of a polypeptide. (3 marks)

A
  1. Because base sequence;
  2. In triplets
  3. Determines order of amino acid sequence
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19
Q

Define the term exon (1 mark)

A

Base coding for sequence of amino acids

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20
Q

What are three differences between DNA in the nucleus
of a plant cell and DNA in a prokaryotic cell? (3 marks)

A
  1. Introns v no introns;
  2. Linear v circular;
  3. No plasmids v plasmids;
21
Q

Define ‘non-coding base sequences’ and describe where the non-coding multiple repeats are positioned in the genome. (2 marks)

A
  1. DNA that does not code for sequences of amino acids.
  2. Positioned between genes
22
Q

Suggest one way the structure of the chromosome could differ along its length to result in the stain binding more in some areas. (1 mark)

A

Differences in base sequences

23
Q

What is a homologous pair of chromosomes? (1 mark)

A

Two chromosomes that carry the same genes

24
Q

Describe how one amino acid is added to a polypeptide that is being formed at a ribosome during translation. (3 marks)

A
  1. tRNA brings specific amino acid to ribosome
  2. Anticodon on tRNA binds to codon on mRNA
  3. Amino acids join by condensation reaction to form peptide bond
25
Q

Describe how mRNA is produced from an exposed template strand of
DNA. (3 marks)

A
  1. Free RNA nucleotides form complementary base pairs
  2. Phosphodiester bonds form
  3. By action of RNA polymerase;
26
Q

Describe how mRNA is formed by transcription in eukaryotes. (5 marks)

A
  1. Hydrogen bonds between DNA bases break;
  2. Only one DNA strand acts as a template;
  3. Free RNA nucleotides align by complementary base pairing;
  4. In RNA Uracil base pairs with adenine on DNA
  5. RNA polymerase joins adjacent RNA nucleotides;
  6. By phosphodiester bonds
  7. Pre-mRNA is spliced to form mRNA
27
Q

Describe how a polypeptide is formed by translation of mRNA. (6 marks)

A
  1. mRNA attaches to ribosomes
  2. tRNA anticodons bind to complementary mRNA codons
  3. tRNA brings a specific amino acid
  4. Amino acids join by peptide bonds
  5. tRNA released after amino acid joined to polypeptide
  6. The ribosome moves along the mRNA to form the polypeptide
28
Q

What does degenerate mean? (1 mark)

A

More than one codon codes for a single amino acid

29
Q

Explain how non-disjunction mutation changes the number of chromosomes (2 marks)

A
  1. In meiosis
  2. Chromosomes don’t separate
30
Q

Apart from mutation, explain one other way genetic variation within a species is increased. (2 marks)

A
  1. Random fusion of gametes
  2. Produces new allele combinations
31
Q

Define ‘gene mutation’ and explain how a gene mutation can have:
* no effect on an individual
* a positive effect on an individual. (4 marks)

A
  1. Gene mutation = change in the base sequence of DNA
32
Q

A change from Glu to Lys at amino acid 300 had no effect on the rate of reaction catalysed by the enzyme. The same change at amino acid 279
significantly reduced the rate of reaction catalysed by the enzyme.
Use all the information and your knowledge of protein structure to suggest
reasons for the differences between the effects of these two changes. (3 marks)

A
  1. Both negatively charged to positively charged change in amino acid;
  2. Change at amino acid 300 does not change the shape of the active site
  3. Amino acid 279 may have been involved in a (ionic, disulfide or hydrogen) bond and so the shape of the active site changes
33
Q

Explain how the chromosome number is halved during meiosis. (2 marks)

A
  1. Homologous chromosomes pair
  2. One of each pair goes to each daughter cell / to opposite
    poles;
34
Q

Describe the process of crossing over and explain how it increases genetic
diversity. (4 marks)

A
  1. Homologous pairs of chromosomes associate
  2. Chiasmata form
  3. Equal lengths of non-sister chromatids
  4. Producing new combinations of alleles;
35
Q

Explain why all the cells of the body will have this mutation. (2 marks)

A
  1. All cells derived from a single cell by mitosis;
  2. Mitosis produces genetically identical cells
36
Q

What is meant by ‘species richness’? (1 mark)

A

A measure of the number of different species in
a community;

37
Q

Suggest one consideration the scientists had taken into account to make sure their method allowed them to identify accurately the species to which each belonged. [1 marks]

A

Use photographs / use a key

38
Q

Give two ways the students would have ensured their index of diversity was
representative of each habitat. (2 marks)

A
  1. Random samples;
  2. Large number of samples
39
Q

Suggest why biodiversity decreases when farmers use larger fields. (1 mark)

A

Fewer species

40
Q

Farmers are now being encouraged to replant hedges on their land.
Suggest and explain one advantage and one disadvantage to a farmer of replanting hedges on her farmland. (2 marks)

A

Advantage -
1. Greater (bio)diversity so increase in predators of
pests
Disadvantage -
2. Reduced land area for crop growth

41
Q

Explain how human mass at birth is affected by stabilising selection (3 marks)

A
  1. Extreme mass babies least likely to survive
  2. to reproduce and so
  3. less likely to pass on their
    alleles for extreme mass at birth
42
Q

The scientists calculated a P value of 0.03 when testing their null hypothesis.
What can you conclude from this result? Explain your answer. (2 marks)

A
  1. Probability that difference is due to chance is less than 0.05
  2. Reject null hypothesis;
43
Q

Name one source of DNA from an extinct animal? (1 mark)

A

Bone/skin/preserved remains / museums;

44
Q

Other than hunting, suggest two reasons why populations might show very low levels
of genetic diversity. (2 marks)

A
  1. Population might have been very small/genetic bottleneck;
  2. Population might have started with small number of individuals / founder effect;
  3. Inbreeding;
45
Q

Explain why it is more useful to calculate an index of diversity than to record species
richness. (2 marks)

A
  1. Index of diversity also measures population size of each species
  2. So useful because may be many of some species
46
Q

Suggest one reason the scientists used biomass instead of the number of individuals of each plant species when collecting data to measure diversity (1 mark)

A

too time consuming to count individuals

47
Q

Explain how the use of antibiotics has led to antibiotic-resistant strains of bacteria becoming a common cause of infection acquired when in hospital (3 marks)

A
  1. some bacteria have alleles for resistance
  2. resistant bacteria survive and reproduce
  3. more antibiotics used in hospital
48
Q

Give three differences between DNA molecules and tRNA molecules? (3 mark)

A
  1. Deoxyribose v ribose;
  2. Double-stranded v single-stranded;
  3. Many nucleotides v few ;
  4. Thymine v uracil;
  5. Double helix v clover (leaf structure);
  6. Does not bind to amino acid v does bind to amino acid;
  7. No exposed bases v anticodon;
49
Q

Suggest why amino acid replacement changes the properties of a protein? (2 marks)

A
  1. changes the bond
  2. which changes the tertiary structure

Biology Exam Questions (5 decks)

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