Genetics

Question 1

what is the genetic code?

Answer 1

when a sequence of bases codes for an amino acid

Question 2

what is an non-overlapping code?

Answer 2

when an amino acid is only coded for by one triplet

Question 3

what is a degenerate code?

Answer 3

when an amino acid is coded for by more than one triplet

Question 4

State the difference between the structure of mRNA and tRNA

Answer 4

1. mRNA carries the genetic code from the DNA in a nucleus to the cytoplasm
2. mRNA has three adjacent bases
3. tRNA carries amino acids that are used to make proteins to the ribosomes
4. has amino acid binding site and a squeuence of three bases ( anti-codon)

Question 5

explain transcription

Answer 5

1. RNA polymerase attatches to the double helix
2. Hydrogen bonds breaks causing the strand to uncoil
3. One strand acts as a template ( antisense strand) for mRNA
4. RNA polymerase lines up free RNA nucleotides by the antisense strand
5. complementary base pairing occurs which forms a complementary mRNA
6. RNA nucleotides pairs up with bases on the antisense strand
7. RNA polymerase moves along the strand to form the mRNA strand
8. Hydorgen bonds reform after RNA polymerase has passed by
9. When RNA polymerase reaches the stop codon, mRNA detatches and leaves the nucleus through a nuclear pore and into the cytoplasm

Question 6

explain transcription

Answer 6

1. mRNA binds to a ribosome in the cytoplasm
2. tRNA with anticodons attatches to mRNA by cimplemntary base paring.
3. second tRNA molculcule attatches to the next codon on mRNA
4. amino acids on the tRNA are joined by a peptide bond
5. First tRNA moves away
6. Third tRNA molcule binds to the next codon and the amino acid bonds forms another peptide bond
7. second tRNA moves away
8. process continues until a stop codon is reached
9. polypeptide chain moves away

Question 7

how does a gene give rise to more than one protein?

Answer 7

• through post transcription changes
• occurs in the nucleus before translation
• mRNA is modified
• genes contain introns (do not code for amno acids) and exons (codes for amino acids)
• introns and exons are included in transcription
• introns are removed by splicing and exons are joined together randonmly
• different mRNA strands are formed
• more than one amino acid sequence therefore different proteins from one gene

Question 8

what is the process of DNA profiling?

Answer 8

1. DNA sample obtained e.g. blood and saliva
2. PCR used to amplify DNA
3. fluorescent tag added ( used to allow DNA to be seen under u.v light)
4. gel electrophoresis is used to sperate DNA
5. gel viewed under U.V light

Question 9

explain the polymerase chain reaction

Answer 9

1. Reaction mixture containing DNA sample, free nucleotides, primers and DNA polymerase
2. DNA mixture heated to 95 degrees to break hydrogen bonds
3. mixure is then cooled to 50-65 degrees to allow primers to bind to strands
4. reaction heated to 72 degrees to allow the DNA polymerase to function
5. DNA polymerase lines up free DNA nucleotide alongside the template strands where complementary base pairing occurs
6. two new copies of DNA is formed per cycle
7. each cycle doubles the amount of DNA present

Question 10

Explain how gel electrophoresis works?

Answer 10

1. sample of DNA is exposed to restriction enzymes
2. small tank filled with agarose gel and a potential difference is applied
3. DNA fragments is placed on the gel
4. as DNA carries a small negative charge , they move towards the positive terminal
5. the larger they are , the slower they move

Question 11

how is DNA profiling used to identify people?

Answer 11

1. DNA profiles are used.
2. The more DNA bands match the sample DNA, after gel electrophoresis, the closer related