14 - genetic control of protein structure and function

Question 1

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

Answer 1

(In all organisms/DNA,) the same triplet codes for

the same amino acid;

Question 2

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? (1)

Answer 2

64

Question 3

Name the process that removes base sequences from pre-mRNA to form mRNA (1)

Answer 3

Splicing

Question 4

Mutation 1 (at start, on exon) leads to the production of a non-functional protein.
Explain why. (3)

Answer 4

1. (Mutation) changes triplets/codons after that
   point/causes frame shift;
2. Changes amino acid sequence (after
   this)/codes for different amino acids (after this);
3. Affects hydrogen/ionic/sulfur bond (not peptide
   bond);
4. Changes tertiary structure of protein (so nonfunctional);

Question 5

What effect might mutation 2 (on intron) have on the protein produced?
Explain your answer. (2)

Answer 5

1. Intron non-coding (DNA)/only exons coding;
2. (So) not translated / no change in mRNA
   produced / no effect (on protein) / no effect on
   amino acid sequence;

Question 6

For DNA, mRNA and tRNA, state whether:
Hydrogen bonds are present
Number of polynucleotide strands in molecule (2)

Answer 6

Hydrogen bonds:
DNA = yes, mRNA = no, tRNA = yes
DNA = 2, mRNA = 1, tRNA =1

Question 7

ACAGTACTTACGATC
In the space below, give the sequence of bases on the pre-mRNA transcribed from this
strand. (1)

Answer 7

UGU CAU GAA UGC UAG

Question 8

Name the enzyme that allows part of a gene to be transcribed. (1)

Answer 8

RNA polymerase

Question 9

The insertion of the DNA copy in one of the host cell’s genes may cause the cell to
make a non-functional protein. Explain how. (2)

Answer 9

Alters base/nucleotide sequence/causes frame shift;
Different sequence of amino acids in
polypeptide/protein/primary structure;
Alters tertiary structure;

Question 10

Some of the children in the trial developed cancer. How might the insertion of the DNA
have caused cancer? (2)

Answer 10

Affects tumour suppressor gene;
Inactivates (tumour suppressor) gene;
Rate of cell division increased/tumour cells continue to
divide

Question 11

What 2 substances make up the backbone of a pre-mRNA molecule? (1)

Answer 11

Phosphate

Ribose

Question 12

The sequence on a pre-mRNA molecule is:
AUCCGU

Give the sequence of bases on the DNA strand from which this pre-mRNA has been transcribed. (1)

Answer 12

TAGGCA

Question 13

Give one way in which the structure of an mRNA molecule is different from the structure of a tRNA molecule. (1)

Answer 13

(mRNA) Does not contain hydrogen bonds/base pairs
/contains codons / does not contain anticodon /
straight/not folded / no amino acid binding
site/longer;

Question 14

Explain the difference between pre-mRNA and mRNA. (1)

Answer 14

(pre-mRNA) contains introns / mRNA contains only

exons;

Question 15

Explain why the percentages of bases from the middle part of the chromosome and the end part are different. (2)

Answer 15

1. Different genes;
2. Have different (base) sequences / combinations of
   (bases);
3. (Pre-mRNA) transcribed from different DNA/codes
   for different proteins;

Question 16

Hydrolysis and condensation are important in the formation of new adult proteins. Explain how (2)

Answer 16

1. Hydrolysis breaks proteins / hydrolyses proteins / produces
amino acids (from proteins);
2. Protein synthesis involves condensation;
3. Hydrolysis of polysaccharides/lipids

Question 17

Why can many different adult proteins be made using a single type of protein? (1)

Answer 17

Amino acids (from calliphorin) can be joined in different
sequences/rearranged;

Question 18

Why is the DNA that codes for complete toxin longer than mRNA used for translation? (1)

Answer 18

(DNA) contains introns/noncoding
bases / mRNA only
contains exons/coding bases;

Question 19

The genetic code is described as being degenerate. What does this mean? (1)

Answer 19

One/an amino acid (can be) coded for
by more than one triplet;

Accept codon for triplet

Question 20

What is a codon? (2)

Answer 20

1. Triplet/three bases on mRNA;

2. That code for an amino acid;

Question 21

What is the role of RNA polymerase during transcription? (1)

Answer 21

To join nucleotides together to form

mRNA/premRNA/RNA;

Question 22

Explain what is meant by a palindromic sequence (1)

Answer 22

GGATCC same as CCTAGG in
opposite direction;

Accept reads same both
ways/same forward and back

Question 23

Genetic code:

Define Messenger RNA (mRNA)
Relationship between genetic and DNA code?
Define Codon = triplet on mRNA that code for amino acid.

Answer 23

= transfers DNA code (as genetic code) from nucleus to cytoplasm.
Genetic code complementary to DNA code.
= triplet on mRNA that code for amino acid.

Question 24

Features of genetic code:

Degenerate code?
Stop codons?
Non-overlapping?
Universal code?

Answer 24

Degenerate code - one amino acid can be coded for by more than one triplet.

Stop codons - do not code for amino acid, mark end of chain.

Non-overlapping - each nucleotide base only read once.

Universal code - In all organisms/DNA same triplet codes for same amino acid;

Question 25

RNA structure: How many polynucleotide chains? 1 mononucleotide unit made up of?

Answer 25

1 chain | Ribose, phosphate, organic base (C/G/U/A)

Question 26

``` DNA mRNA tRNA no. chains? H bonds? Size? Shape? Backbone? T/U? ```

Answer 26

DNA mRNA tRNA no. chains? 2 1 1 H bonds? y n y Size? largest med smallest Shape? double-helix single-helix clover Backbone? deoxyribose ribose ribose T/U? thymine uracil uracil

Question 27

Transcription (3)

Answer 27

1. DNA helicase breaks H bonds, strands separate, nucleotide bases exposed 2. RNA polymerase moves along template strand, joins nucleotides together to form pre-mRNA 3. Reaches stop codon and detaches

Question 28

Define exons Define introns Splicing? mRNA then?

Answer 28

Code for proteins Do not code for proteins Removes introns forming mRNA mRNA leaves via nuclear pore, attaches to ribosomes in cytoplasm

Question 29

Translation (5)

Answer 29

1. Ribosome attaches to start codon of mRNA. 2. tRNA with complementary anticodon pairs up with mRNA - carries 1 amino acid. 3. Ribosome joins 2 tRNA at a time, 2 amino acids joined by peptide bond. 4. Previous tRNA released. 5. Reaches stop codon, all detach - polypeptide chain formed.

Question 30

How is the quaternary structure of a protein formed? (3)

Answer 30

Polypeptide coiled/folded, coiled/folded further, linked together

Question 31

# Define mutation Give 1 benefit of a mutation

Answer 31

change to the quantity or structure of the sequence of bases in DNA. (Inheritable if occur during gamete formation) Genetic diversity - natural selection and speciation

Question 32

Substitution mutation: Define substitution mutation Nonsense mutation? (2) Mis-sense mutation? (2) Silent mutation? (2)

Answer 32

= nucleotide replaced by nucleotide with different base = stop codon, nonfunctional final protein = different amino acid coded for, nonfunctional final protein. = same amino acid coded for (degenerate code), functional final protein

Question 33

Deletion mutation: Define deletion mutation How does a deletion mutation result in non-functional protein? (4) Where does it have greatest effect?

Answer 33

= Nucleotide lost. 1. Changes triplets/causes frame shift; 2. Changes amino acid sequence 3. Affects hydrogen/ionic/sulfur bond 4. Changes tertiary structure of protein so nonfunctional At start of DNA

Question 34

# Define mutagenic agent 2 examples?

Answer 34

= outside factor that increases natural mutation rate High energy radiation, chemicals

Question 35

Proto-oncogenes: Define proto-oncogenes In normal cell? (3) Mutation causes? In mutated cell? (3)

Answer 35

= stimulate/speed up cell division Growth factors attach to receptors on membrane ‘switch on’ genes for DNA replication via relay proteins. Normal cell division Proto-oncogenes to develop into oncogenes Receptors on membrane permanently activated Genes for DNA replication permanently ‘switched on’ Excessive cell division - tumour formation

Question 36

Tumour suppressor genes: Define tumour suppressor genes Mutation causes? In mutated cell? Tumour types? (2)

Answer 36

= inhibit/slow cell division Inactivation Cell division increases Tumour formation Malignant tumour = a harmful tumour Benign tumour = a harmless tumour