4.3.6-Mutations & MeiosisA-A* (AO3/4) - DNA,Genes

Question 1

Mitochondria contain their own DNA which is evidence for the theory of endosymbiosis. All the mitochondria found in a zygote originate in the egg cell as the sperm cell only donates its DNA to the zygote.

Explain the pattern of inheritance shown in the pedigree.

1-Describe the pattern of inheritance

Answer 1

1-When the mother is infected, all the offspring will inherit the disease whether they are female or male. When the father is not infected, no
offspring will show symptoms of the disease.

Question 2

Hypothesize where the disease gene may be located

Answer 2

If inheritance of the disease relies on the mother being infected, then only the mother can pass on the disease. The cellular components that are passed on exclusively by the mother are the mitochondria. This suggests that the gene which causes the disease is located on the mitochondrial DNA.

Question 3

Explain how bases code for proteins

Answer 3

Proteins are polymers of 
amino
acid
monomers. DNA is transcribed into 
mRNA which is modified and exported from the 
nucleus to the 
cytoplasm. 

Three bases of the transcript form what is known as a codon. The
ribosome
translates the transcript and each codon
codes for one
amino
acid.

Question 4

Substitution mutation

Answer 4

A substitution changes 
1 base in the mRNA sequence. This can cause a 
missense mutation (if the new codon codes for a different amino acid) or a 
nonsense mutation (if the new codon is a 
STOP codon). Some amino acids are coded for by 
multiple codons so there is a chance that a substitution does not actually change the amino acid sequence.

Question 5

3 base deletion

Answer 5

three-base deletion might remove a single codon, or remove some bases from two codons. In the end, only
1
one amino acid will be lost from the protein and one amino acid may be
changed. This can cause a missense or
nonsense
nonsense mutation as well.

Question 6

single base edition

Answer 6

The ribosome reads the codons in order, one after the other, and does not overlap the codons when it reads. When the number of bases changes by a number other than a multiple of 3, a frame shift occurs. This means that reading frame of the ribosome is changed and all future codons are read wrong. This mutation is the most likely to create a non-functional protein.
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Question 7

Prokaryotes can carry out co-transcriptional translation but eukaryotes cannot.

Why is this the case?

Answer 7

Prokaryotes do not have a nucleus. This means that ribosomes and DNA are both located in the cytoplasm. As RNA Polymerase transcribes the DNA, ribosomes can bind to the mRNA coming out of the RNA polymerase enzyme and start translating it.

Eukaryotic genes have introns. These introns must be spliced out of the pre-mRNA before it can be exported to the cytoplasm and translated.

Question 8

What role does RNA play in protein synthesis?

Answer 8

• mRNA- is produced as a transcript of the DNA code. mRNA transfers the code of the gene from the nucleus to the cytoplasm
• tRNA- is the translator of the genetic code. Each tRNA binds to a specific amino acid and to a specific mRNA codon. In this way tRNA determines which amino acid each codon codes for
• rRNA- is a major part of a ribosome. rRNA carries out catalytic and structuraal roles in the ribosomes. It is essential protein synthesis

Question 9

Q1.(a) A mutation can lead to the production of a non-functional enzyme. Explain how

Answer 9

1. Change / mutation in base / nucleotide sequence (of DNA / gene);
   Q.
   Ignore: references to changing base-pairing
   Accept: affect for change, if in correct context
   Accept: changes triplets / codons
2. Change in amino acid sequence / primary structure (of enzyme);
   Accept: different amino acid(s) coded for
   Q Reject: different amino acids produced / formed / made
3. Change in hydrogen / ionic / disulfide bonds;
   Accept: references to sulfur bonds
4. Change in the tertiary structure / shape;
   Neutral: alters 3D structure / 3D shape
5. Change in active site;
6. Substrate not complementary / cannot bind (to enzyme / active site) / no
   enzyme-substrate complexes form.
   Accept: no E S complexes form