DNA and Protein Synthesis

Question 1

What are the differences between prokaryotic and eukaryotic DNA?

Answer 1

• Prokaryotic DNA is circular as plasmids while eukaryotic has linear DNA
• Prokaryotic DNA is smaller than eukaryotic DNA
• Eukaryotic DNA has associated proteins while prokaryotic doesn’t
• Eukaryotic DNA forms chromosomes while prokaryotic doesn’t
• Eukaryotic DNA has non coding sections (introns and mini satellites) while prokaryotic doesn’t

Question 2

Define gene

Answer 2

A section of DNA that codes for a particular protein

Question 3

Define locus

Answer 3

The fixed position of a gene on a DNA molecule

Question 4

Define triplet

Answer 4

A sequence of 3 DNA nucleotides that codes for a specific amino acid

Question 5

Define codon

Answer 5

Three bases on mRNA that code for a specific amino acid

Question 6

Define allele

Answer 6

Different form of the same gene

Question 7

Define genome

Answer 7

The complete set of genes required to build a functional organism

Question 8

Define proteome

Answer 8

The complete set of proteins produced by a genome at any one time

Question 9

Define degenerate

Answer 9

Some amino acids are coded for by more than one codon

Question 10

Define non overlapping

Answer 10

Each base is part of only one triplet

Question 11

Define universal

Answer 11

In all organisms, the same triplet codes for the same amino acid

Question 12

What is the non-coding region between genes called (eukaryotic DNA)?

Answer 12

Mini satellites

Question 13

What is the non-coding region within genes called (eukaryotic DNA)?

Answer 13

Introns

Question 14

Compare the structure of mRNA and tRNA.

Answer 14

• mRNA is linear with no H bonds while tRNA is in a cloverleaf shape and has H bonds
• tRNA has an amino acid binding site but mRNA doesn’t
• mRNA can be different lengths while tRNA is similar in length
• mRNA has a codon while tRNA has an anticodon

Question 15

Compare and contrast the DNA in eukaryotic cells with the DNA in prokaryotic cells. (5)

Answer 15

Comparisons
1. Nucleotide structure is identical;
2. Nucleotides joined by phosphodiester bond; OR Deoxyribose joined to phosphate (in sugar, phosphate backbone);
3. DNA in mitochondria / chloroplasts same / similar (structure) to DNA in prokaryotes

Contrasts
4. Eukaryotic DNA is longer;
5. Eukaryotic DNA contain introns, prokaryotic DNA does not;
6. Eukaryotic DNA is linear, prokaryotic DNA is circular;
7. Eukaryotic DNA is associated with / bound to protein / histones, prokaryotic DNA is not

Question 16

Explain how a change in the DNA base sequence for a protein may result in a change in the structure of the protein. (3)

Answer 16

1. Change in amino acid/s /primary structure;
2. Change in hydrogen/ionic/ disulfide bonds;
3. Alters tertiary structure

Question 17

What is the structure of a ribosome?

Answer 17

They are composed of two subunits made from rRNA and proteins. In eukaryotes they are 80s but in prokaryotes they are 70s (smaller)

Question 18

What are the stages of transcription?

Answer 18

1. DNA helicase breaks hydrogen bonds between DNA strands
2. Only one strand acts as a template
3. RNA nucleotides are attrected to exposed bases according to base rule pairing
4. RNA polymerase joins RNA nucleotides together
5. (Only in eukaryotes) pre-mRNA is spliced to remove introns

Question 19

What are the stages of translation?

Answer 19

1. Ribosomes bind to mRNA
2. Ribosome moved to the start codon (AUG)
3. tRNA carries a specific amino acid. The anticodon of the tRNA is complimentary to the codon on mRNA
4. Ribosome moves along to next codon
5. Amino acids joined together using energy from ATP to form a polypeptide, as a peptide bond is created
6. The ribosome releases the mRNA once the stop codon is reached

Question 20

mRNA is used during translation to form polypeptides. Describe how mRNA is produced in the nucleus of the cell. (6)

Answer 20

1. Helicase;
2. Breaks hydrogen bonds;
3. Only one DNA strand acts as template;
4. RNA nucleotides attracted to exposed bases;
5. (Attraction) according to base pairing rule;
6. RNA polymerase joins (RNA) nucleotides together;
7. Pre-mRNA spliced to remove introns.

Question 21

Starting with mRNA in the nucleus of the cell, describe how a molecule of protein is synthesised. (6)

Answer 21

1. mRNA leaves nucleus through nuclear pore.
2. To ribosome.
3. tRNA molecules bring amino acids to ribosome.
4. Specific tRNA molecule for specific amino acid.
5. Anticodon of tRNA corresponds / complementary to codon on mRNA.
6. Peptide bonds form between amino acids.
7. tRNA detaches and collects another amino acid.
8. Ribosome moves along mRNA.