Genetics and Diversity - Protein Synthesis

Question 1

What is the minimum number of base pairs that code for each amino acid and why?

Answer 1

3 base pairs:

as there are only 4 bases, two pairs would not produce the range of amino acids that we use

Question 2

What is degenerate code?

Answer 2

When more that one triplet is needed for an amino acid

Question 3

What is a codon/triplet?

Answer 3

3 base pairs that codes for a specific amino acid or signals the start or end of a sequence

Question 4

Which direction do the left and right strands of DNA run in?

Answer 4

Left: 5’ to 3’

Right: 3’ to 5’

Question 5

What are the functions of the antiparallel strands in DNA?

Answer 5

1. maintains 2 copies of the DNA in case of mutation
2. protects the bases
3. required for semi-conservative replication
4. improves molecular stability

Question 6

What is a gene?

Answer 6

A section of DNA on a homologous chromosome at a specific position (the locus)

Question 7

What information does a gene carry?

Answer 7

The information to produce the amino acid sequence of a polypeptide

Question 8

What are the features of prokaryotic DNA?

Answer 8

1. free in the cytoplasm - no nucleus
2. naked
3. singular circular chromosome
4. may contain plasmids

Question 9

What is a plasmid?

Answer 9

a smaller, separate loop of DNA

Question 10

What are the features of eukaryotic DNA?

Answer 10

1. Located in a double membrane-bound nucleus
2. Wound around histone proteins
3. Multiple linear chromosomes
4. No plasmids

Question 11

What are introns?

Answer 11

Sections of DNA that don’t code for polypeptides (non-coding DNA)

Question 12

What are exons?

Answer 12

Coding sequences of DNA

Question 13

How many chromosomes do humans have?

Answer 13

46 chromosomes or 23 homologous pairs

Question 14

What are the differences betwen RNA and DNA?

Answer 14

1. Uracil used instead of Thymine in RNA
2. RNA only has 1 strand
3. RNA - ribose sugar, DNA - deoxyribose sugar
4. RNA is shorter than DNA

Question 15

What are the 3 types of RNA?

Answer 15

mRNA

tRNA

rRNA

Question 16

What is the general function of RNA?

Answer 16

to transfer coded information from DNA into the cytoplasm where it can be translated into proteins

Question 17

What does mRNA stand for?

Answer 17

messenger RNA / messenger ribonucleic acid

Question 18

What is the function of mRNA?

Answer 18

to transcribe the code for the gene in the DNA and carry it from the nucleus to the cytoplasm

Question 19

What are the features of mRNA?

Answer 19

can travel through nuclear pores

single stranded helix

has a short lifetime

Question 20

What does tRNA stand for?

Answer 20

transfer RNA / transfer ribonucleic acid

Question 21

What is the function of tRNA?

Answer 21

to match the triplet code in mRNA to their respective amino acids

Question 22

What are the features of tRNA?

Answer 22

only 80 nucleotides long

folds up by complementary base pairing to form a 3D looped clover structure

middle loop contains the anticodon

Question 23

What is an anticodon?

Answer 23

the tRNA codon complimentary to an mRNA codon that attaches the appropriate amino acid

Question 24

What does rRNA stand for?

Answer 24

ribosomal RNA / ribosomal ribonucleic acid

Question 25

What is the function of rRNA?

Answer 25

to work with proteins to synthesise ribosomes

Question 26

What is transcription?

Answer 26

The process of making pre-mRNA using part of the DNA as a template/coding strand

Question 27

What are the stages of transcription?

Answer 27

1. RNA polymerase binds to section of DNA
2. Hydrogen bonds are broken, exposing the bases
3. Nucleotides on template strand bind to complementary RNA molecules
4. RNA polymerase moves along the strand, joining the RNA nucleotides together and releasing them
5. DNA strands rejoin once RNA polymerase has passed
6. RNA polymerase reaches stop codon and detaches

Question 28

Why does pre-mRNA need to be spliced?

Answer 28

Because the sequence includes both introns and exons, so the introns need to be removed

Question 29

Why does prokaryotic mRNA not need to be spliced?

Answer 29

Prokaryotic DNA contains no introns

Question 30

How can the same sequence of DNA code for several proteins?

Answer 30

the exon sections can be joined together in different ways during splicing, producing different sequences

Question 31

What is splicing?

Answer 31

the process of removing introns from pre-mRNA and joining the exons together to form mature mRNA

Question 32

What is translation?

Answer 32

the process of converting the codon sequence in the mRNA molecule into an amino acid sequence

Question 33

What are the stages of translation?

Answer 33

1. mRNA leaves nucleus after splicing
2. a ribosome attaches to the start codon
3. the complementary tRNA molecule binds to the first codon
4. a second tRNA molecule binds to the second codon
5. a peptide bond forms between the 2 amino acids
6. the ribosome moves along the mRNA to the next codon and the first tRNA is released
7. the process repeats until the stop codon is reached

Question 34

What catalyses the peptide bond during translation?

Answer 34

enzymes and ATP

Question 35

How many amino acids can be added per second during translation?

Answer 35

15

Question 36

What is post-translational modification?

Answer 36

the process of modifying proteins so that they can become fully functional - secondary, tertiary and quaternary protein structures

Question 37

What carries out post-translational modification?

Answer 37

enzymes