AQA AS Biology

Topic Questions

4.1 DNA, Genes & Chromosomes

1a2 marks

Describe two differences between the DNA in prokaryotic cells and the DNA in eukaryotic cells.

1b2 marks

Figure 1 shows a part of a DNA molecule.

Figure 1

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Figure 1

Name the parts X and Y

 

i)  X ..............................................................

 

ii) Y ..............................................................

 

1c2 marks

A gene is a small section of DNA. State what a gene codes for.

1d1 mark

Explain why the genetic code is described as being universal.

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2a2 marks

State the cells that chromosomes X and Y would be sourced from in Figure 1

Figure 1

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iX ...............................................................

 

ii) Y ..............................................................

2b2 marks

Figure 2 below shows maternal and paternal chromosomes with the alleles of four different genes shown.

Figure 2

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i)  Identify the structure labelled X

 

ii) Annotate the diagram to show the locus of gene B.

2c1 mark

The genetic code uses four different DNA bases. What is the maximum number of different DNA triplets that can be made using these four bases?

2d2 marks

Name the two non-coding regions of eukaryotic nuclear DNA? 

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3a2 marks

The table below shows properties of a DNA molecule. Use a to identify which are the properties of prokaryotic DNA molecules.

 

Properties of DNA molecules

Prokaryotes

 Short

 

 Linear

 

 Associated with histones 

 

 Non-coding regions present

 

 Circular

 
3b1 mark

State why it is possible for a gene from one organism to be introduced into and function in a different organism.

3c2 marks

Figure 1 below shows part of a DNA molecule.

Figure 1

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i) Name the component of the DNA molecule labelled X.

ii) This part of the DNA molecule represents a small section of a gene. Give the term for the fixed position a gene occupies on a chromosome.

 

3d1 mark

Figure 2 below shows part of a DNA molecule.

Figure 2

e-q3-2

State the maximum number of amino acids for which this piece of DNA could code.

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4a1 mark

State the smallest molecule that can be altered by a mutation and result in a change to the coding of a polypeptide?

4b2 marks

Figure 1 shows a short sequence of DNA bases from the nucleus of a eukaryotic cell.

Figure 1

A A A C A G G A C A T C A A T T G G A G C A T A G G T C C A

i) State the maximum number of amino acids for which this piece of DNA could code.

ii) The number of amino acids coded Figure for could be fewer than the answer to i).Give one reason why.
4c2 marks

State what the chromosomes of fungi are made of.

4d1 mark

The codons ACU and ACG both code for the amino acid threonine. Identify the property of the genetic code that this illustrates.

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5a3 marks

Describe three differences between mitochondrial DNA and nuclear DNA. 

5b1 mark

Give the name of the maternal and paternal pairs of chromosomes in an offspring.

5c2 marks

Figure 1 below shows a small section of nuclear DNA from a eukaryotic cell. Annotate the diagram to show which section/s represent the non-coding base sequences and which represent the coding base sequences.

Figure 1

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5d2 marks

State where telomeres are found within a chromosome as well as their function.

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1a1 mark

State the molecules that make up a ribosome. 

1b1 mark

Table 1 shows a sequence of DNA. Complete Table 1

Table 1

DNA Coding Strand


A


C


C


G


T


A


T


G


mRNA

               



1c5 marks

Table 2 shows a sequence of DNA bases and the mutated version of the same sequence. Table 3 shows the DNA triplets that code for some amino acids.

Table 2

Position

1

2

3

4

5

6

7

8

9

10

11

12


Original sequence

A

C


T


A


A


A


C


G


G


T


A


C


Mutated sequence


A


C


T


A


A


C


G


G


T


T


A


C

 Table 3

DNA Triplets

Amino Acid

ACT, ACC, ACA, ACG

Thr

TTT, TTC

Phe

AGA, AGG, CGT, CGC, CGA, CGG

Arg

TAT, TAC

Tyr

GGT, GGA, GGG, GGC

Gly

AAA, AAG

Lys

AAT, AAC, GAT, GAC

Asp

Two single base mutations have occurred. Use the information provided in Table 2 and Table 3 to state and explain the mutations and their effect on the amino acids that will be produced from the mutated DNA sequence.

1d2 marks

Suggest the effect of the two single mutations from part c) could have on the protein structure coded by this mutated sequence of DNA. 

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2a3 marks

Some species of organisms can have the same percentage of bases as other organisms yet they can still be very different animals. Explain why. 

2b3 marks

In all living organisms the ratio (C + A) ÷ (G + T) is constant but the ratio of   (A + T) ÷ (C + G) can vary between organisms. Using your knowledge of the structure  and function of DNA, explain this information.  

           

2c1 mark

Explain why the DNA which codes for the human protein, alpha globin, has 850 base pairs but there are only 141 amino acids in this protein.

2d4 marks

Tumour suppressor genes code for proteins that control cell division in cells. Describe and explain how a mutation in a tumour suppressor gene could lead to a malignant tumour.

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3a2 marks

Proteins are produced in two stages. Different types of RNA molecules are required within these stages. Table 1 shows the various types of RNA and the total percentage of each within the cell of a desert rat.  

Table 1

Type of RNA

Percentage of total RNA

RNA in the nucleus

14

mRNA

6

rRNA

62

tRNA

18

Use the information in Table 1 and explain which organelle would contain the greatest percentage of RNA. 

3b2 marks

A typical cell from a desert rat contains approximately 43 000 000 000 RNA nucleotides.Using Table 1 and the information given calculate the approximate number of tRNA nucleotides in the cell of a desert rat. Give your answer in standard form and to two significant figures. 

3c3 marks

Explain why desert rat cells contain a large number of different mRNA nucleotides but only 64 different tRNA molecules.  

3d2 marks

Some mutations can result in a frameshift. Describe and explain what is meant by a  frameshift and how this may affect the protein made.

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4a2 marks

Table 1 shows the amino acids coded for by each of the mRNA codons. It also shows the properties of some of the amino acids. 

Table 1

First Base                   Second Base Third Base
U C A G
U

Phe



Leu

Ser

Tyr



Stop
Cys U
Stop C
Trp A
Trp G
C Leu

Pro

His+

Arg+ U
C

Gln
A
G
A Ile

Thr Asn

Ser U
C

Met

Lys+
Arg+ A
G
G

Val

Ala Asp-

Gly U
C

Asp-
A
G

Key

+ Represents amino acids with a positive charged R group

- Represents amino acids with a negative charge R group

Use information from Table 1 to explain, using an example, why the DNA code is said to be degenerate. 

4b3 marks

A scientist investigated the structure of an enzyme containing 647 amino acids. She looked at mutations that commonly occurred and their effects on the protein structure.The mutations were all single base substitutions. 

One of the changes she discovered was at position 389 where Asp was substituted for Glu. 

Use Table 1 to suggest the likely effect of this mutation on the protein structure. 



4c2 marks

Table 2 shows the positions of three different single base substitutions.  

Table 2

Position of amino acid

Original amino acid

Amino acid after mutation

238

Gln

Pro

531

Lys

Thr

109

Asn

Arg

The mutation at position 531 did not affect the enzymes structure but the mutation at position 109 did. Using your knowledge of protein structure and information from Table 2  to explain this. 

4d1 mark

Use information from Table 1 to tick one box that shows which single base mutation below would result in the amino acid Leu being replaced with the amino acid Arg. 

Table 1

UUA → GCA

 

UUG → UUC

 

CUA → CGA

 

AAG → AUC

 

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5a3 marks

There are several different types of gene mutation that can occur within a sequence of DNA. Figure 1 shows a section of a gene with two different substitutions. 

Figure 1

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Explain why a substitution at point A will not lead to a change in protein structure but a substitution at point B can.

5b4 marks

Further along in the DNA strand, beyond point B in the coding region, there was a further substitution of a base. This also did not lead to any changes in the protein structure and function. Suggest and explain two reasons why. 

5c2 marks

Scientists have discovered that within species genomes regions of introns do not change in frequency at the same rate as exons. Explain why.  

5d2 marks

Cytosine and guanine can be bonded together in two ways, in a dinucleotide or in a base pair. Explain how these bonds differ. 

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1a6 marks

The synthesis of proteins is determined by the genetic code. The genetic code is provided by the sequence of nucleotides in DNA. As the code is the same for almost all organisms it is described as universal. 

Name and describe the other features of the genetic code.

1b1 mark

Identify the structure labelled X in Figure 1.

Figure 1

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1c1 mark

Papain is an enzyme. It is 345 amino acids long.

State the minimum number of DNA bases needed to code for papain?

1d1 mark

Figure 2 shows the sequence of DNA bases coding for ten amino acids in the enzyme papain.

Figure 2

C  A  A  T  T  T  C  A  A  A  G  T  T  G  C  T  T  T  T  T  G  T  T  G  C  A  A  T  A  T

The number of each type of amino acid coded for by this sequence of DNA bases is shown in Table 1.

Table 1

Amino acid

Number present

Gln

3

Leu

2

Phe

2

Tyr

1

Cys

1

Ser

1

Use Table 1 and Figure 2 to determine the sequence of amino acids in this part of the enzyme. Write your answer in Figure 3.

Figure 3.

 

Phe

 

Ser

         

Tyr

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2a1 mark

Lactase is an enzyme that is used to produce lactose-free milk. A student was given the RNA sequence of the enzyme lactase in Figure 1 and was asked to use Table 1 to identify the first four amino acids of lactase.  

Figure 1

A U G G A A C U C U C U

Table 1 shows the genetic code (mRNA codons).

Table 1B-Fc7btd_m-q2

2b4 marks

Describe and explain how the mRNA nucleotide sequence worked out to correspond to the first four amino acids using Table 1 may not be the same as the mRNA nucleotide sequence for those amino acids present in a typical bacterial cell.

2c2 marks

In an electron micrograph, a DNA molecule appears 1.5 mm wide, however the actual width of a DNA molecule is 2 nm. What is the magnification?

2d4 marks

Figure 2 shows the stages that occur to produce a part of a polypeptide (found in a human).

Figure 2

m-figure-2

Explain the features of the genetic code that the diagram illustrates.

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3a2 marks

The genetic code is described as degenerate. 

Describe what is meant by this, using an example from Table 1 to illustrate the answer.

Table 1

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3b3 marks

State where the DNA molecule in Figure 1 would be found and explain why?

Figure 1

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3c3 marks

Annotate Figure 2 to illustrate the following terms: 

i) Locus        ii) Gene        iii) Centromere 

Figure 2

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3d2 marks

Figure 3 illustrates a small section of a DNA molecule from the nucleus of a eukaryotic cell.

Name the structures labelled X and Y.

Figure 3

m-q3-3

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4a3 marks

Distinguish between mitochondrial DNA and nuclear DNA of eukaryotic cells.

4b1 mark

On Figure 1 circle the hydrogen bond between the guanine and cytosine bases?


Figure 1

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4c4 marks

Compare the sizes and structures of prokaryotic and eukaryotic chromosomes. 

4d1 mark

Myoglobin is a eukaryotic  protein consisting of a single polypeptide chain of 153 amino acids.

State the minimum number of DNA bases needed to code for Myoglobin?

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5a3 marks

The haemoglobin molecule consists of four polypeptide chains: two ? and two ? chains. Table 1 shows some of the first seven amino acids of the ? chain of haemoglobin and the bases in the sequence of DNA that code for these seven amino acids.

Table 1

Amino acid sequence

Met

 

Leu

   

Ala

Asp

Base sequence in DNA

ATG

GTG

CTG

TCT

CCT

GCC

GAC

 

Table 2 shows the codons that code for seven amino acids.

Table 2

G29O3F0A_m-q2Using Table 2 determine the missing amino acids and complete Table 1.

5b1 mark

Figure 1 shows part of the mRNA and its corresponding amino acid sequence fo cytochrome c, a protein involved in aerobic respiration, for Mus musculus (house mouse)and Loxodonta africana (African elephant). 

Figure 1

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Identify the DNA triplet that codes for the amino acid serine (Ser).

5c3 marks

Figure 2 shows part of the mRNA and its corresponding amino acid sequence for cytochrome c, a protein involved in aerobic respiration, for Gorilla gorilla (gorilla)and Loxodonta africana (African elephant).

Figure 2

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Explain how Figure 2 illustrates the genetic code.

5d6 marks

Compare the DNA in prokaryotic cells with the DNA in the nucleus of eukaryotic cells.

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