exam Q genetics

Question 1

Describe how a gene is a code for the production of a polypeptide

Answer 1

1.base sequence;
2. (In) triplet(s);
3. (Determines) order/sequence of amino acid sequence/primary
structure (in polypeptide)

Question 2

Describe how a phosphodiester bond is formed between two nucleotides
within a DNA molecule.

Answer 2

1. Condensation (reaction)/loss of water;
2. (Between) phosphate and deoxyribose;
3. (Catalysed by) DNA polymerase;

Question 3

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

Answer 3

triplets of bases codes for more than one amino acid

mutations can occur in introns

Question 4

Give one other difference between the structure of a DNA nucleotide and
the structure of an RNA nucleotide.

Answer 4

Deoxyribose in DNA and ribose in RNA;

Question 5

Compare and contrast the DNA in eukaryotic cells with the DNA in
prokaryotic cells.

Answer 5

same
Nucleotide structure is identical;
Nucleotides joined by phosphodiester bond;

difference
-eukaryotic is longer
-eukaryotic contain introns
-eukaryotic DNA is linear
-eukaryotic DNA is associated with proteins

Question 6

what is a homologous pair

Answer 6

two chromosomes that carry the same genes

Question 7

Describe how one amino acid is added to peptide that is being formed at the ribosome

Answer 7

tRNA brings a specific amino acid

Anti codon on tRNA binds to codon on the mRNA

Amino acids join by condensation reaction using ATP

Question 8

Describe how a polypeptide is formed by translation

Answer 8

1. mRNA binds to ribosome
   2.)the tRNA anticodons binds to complementary codons on the mRNA
   3.)tRNA brings specific amino acid
2. Amino acid join by peptide bonds
3. Amino acids join using ATP
4. tRNA is released
5. The ribosome moves along the mRNA to form polypeptide

Question 9

Give two structural differences between mRNA and tRNA

Answer 9

mRNA does not have hydrogen bonds

mRNA does not have an amino acid binding site

mRNA has more nucleotides

Question 10

Describe how mRNA is formed

Answer 10

1.hydrogen bonds between base pairs are Brocken
2.only one DNA strand acts as a template
3. Free RNA nucleotides align by complementary base parings
4. Uracil pairs with adenine
5. RNA polymerase joins adjacent nucleotides
6. By phosphodiester bonds

Question 11

Define the term mutagenic agent

Answer 11

A factor that increases the rate of mutations

Question 12

Apart from mutation ,explain one other way genetic variation in a species is increased

Answer 12

Random fusion of gametes
Produces new allele combinations

Question 13

Define gene mutation and how gene mutation can have no effect on an individual or a positive effect on an individual

Answer 13

Change in base sequence in DNA
Results in the formation of a new allele
Genetic code is degenerate
Therefore it doesn’t not change amino acid
New allele is recessive so does not influence phenotype
Results in change in polypeptide

Question 14

Describe the process of crossing over and explain it increasing genetic diversity

Answer 14

1. Homologous pairs form bivalent
   2.chiadma forms
2. Equal lengths of chromatids are exchanged
   4.producing new allele combinations