6: Nucleic Acids and Protein Synthesis

Question 1

What is a purine and give examples

Answer 1

A nitrogenous base with a double ring structure;
Adenine and Guanine

Question 2

What is a pyrimidine and give examples

Answer 2

Nitrogenous bases with a single ring structure;
Uracil, Cytosine and Thymine

Question 3

Structure of a nucleotide

Answer 3

Phosphate group;
Pentose sugar;
Nitrogenous base with a

Question 4

Compare the structure of DNA and RNA nucleotides

Answer 4

Similarities
Both have a pentose sugar, a phosphate group and a nitrogenous base;
Both have Adenine, Cytosine and Guanine;
Bothe are linked by phosphodiester bonds between 5’ and 3’ carbon atoms
Differences
RNA has a ribose sugar while DNA has a deoxyribose sugar;
RNA has Uracil while DNA has thymine;
RNA is single stranded while DNA is double stranded;
DNA is a longer molecule than RNA

Question 5

How does the formation of DNA differ between leading and lagging strands

Answer 5

On the leading strand the new DNA is synthesiszed continuously;
On the lagging strand it is synthesized in small segments (Okazaki fragments)

Question 6

What is the function of DNA ligase

Answer 6

To join Okazaki fragments together to form a continuous DNA strand in the lagging strand;
By catalysing the formation of phosphodiester bonds between adjacent nucleotides

Question 7

What is the importance of hydrogen bonding in the structure of a DNA molecule

Answer 7

Hydrogen bonds hold two polynucleotide strands together;
The hydrogen bonds stabilize the DNA molecule;
Contributes to the double helix structure of the DNA molecule

Question 8

Compare the structure of ATP and DNA nucleotides

Answer 8

Similarities
They have a nitrogenous base, a pentose sugar and a phosphate group;
Differences
DNA has Cytosine, Adenine, Thymine and Guanine while ATP only contains Adenine;
ATP has three phosphate groups while DNA has one;
ATP has a ribose sugar while DNA has a deoxyribose sugar

Question 9

How does the structure of mRNA enable it to perform its function

Answer 9

It is a single stranded molecule;
So it is able to fit through the nuclear pore and leave the nucleus to reach the ribosomes

Question 10

What does semi conservative mean

Answer 10

Each DNA strand acts as a template for the synthesis of a new strand;
The new DNA molecule contains one original strand and one new strand

Question 11

How does DNA replicate

Answer 11

DNA unwinds;
DNA helicase unzips the molecule;
Hydrogen bonds between complementary base pairs break;
Both strands are used as templates;
DNA polymerase binds on to the template strands;
The leading strand is copied continuously while the lagging strand is copied in short segments;
DNA ligase joins the Okazaki fragments by catalysing the formation of phosphodiester bonds;
Leading to two identical DNA molecules produced

Question 12

What is a gene

Answer 12

A sequence of polypeptides that forms part of a DNA molecule;
Which codes for a specific polypeptide

Question 13

What is a gene mutation

Answer 13

A change in the sequence of base pairs in a DNA molecule that may result in an altered polypeptide

Question 14

What are the ways a mutation in the DNA base sequence can occur

Answer 14

Insertion of nucleotides;
Deletion of nucleotides;
Substitution of nucleotides

Question 15

Advantage of the genetic code being degenerate

Answer 15

Less chance of mutation

Question 16

Causes of gene mutation

Answer 16

Error during DNA replication;
Damage due to mutagens

Question 17

Effects of gene mutation on proteins

Answer 17

Structural proteins (collagen) may lose their strength;

Question 18

Function of RNA polymerase

Answer 18

Unwinds the DNA molecule at the start of a gene;
Joins free nucleotides to mRNA molecule;

Question 19

Describe post transcriptional modification

Answer 19

Introns which are non coding sequences are removed;
Exons are fused together to form mature mRNA;
This process is splicing

Question 20

Importance of the genetic code being universal

Answer 20

The same codons code for the same amino acids in all organisms;
Genetic info is transferable between species;
Useful in genetic engineering

Question 21

Difference between mRNA and tRNA

Answer 21

mRNA dies not have h binds while tRNA does;
mRNA contains codons while tRNA contains anticodons;
mRNA is a straight molecule while tRNA is clover shaped/ folded;
mRNA is longer than tRNA;
tRNA has an amino acid binding site while mRNA does not

Question 23

Structure of a tRNA molecule

Answer 23

It has a clover shap;
With double stranded sections held together by h bonds;
It has three exposed bases which form an anticodon;
It has an amino acid binding site

Question 24

Importance of tRNA in translation

Answer 24

It binds with a specific amino acid and brings it to the mRNA;
Its anticodon pairs with a complementary codon on the mRNA and forms hydrogen bonds;
Two tRNA molecules fit on the ribosome and bring their amino acids close together;
To form a peptide bond

Question 25

What is the role of the ribosome in translation

Answer 25

mRNA attatches to the ribosome; tRNA carries a specific amino acid to the mRNA molecule on the ribosome; The tRNA anticodons binds to the complementary codon on the mRNA; The ribosome allows for two tRNA molecules to fit onto it at the same time; Bringing their amino acids together and forming peptide bonds; The ribosome moves along the mRNA one codon at a time until a stop codon is reached

Question 26

Role of DNA in protein synthesis

Answer 26

DNA contains genes which code for a specific polypeptide; It provides a template strand for the formation of mRNA

Question 27

Importance of start and stop signals in a DNA molecule

Answer 27

Indicate where an individual gene starts and stops; Which ensures DNA is read correctly and the code is non- overlapping In order to produce the correct sequence of amino acids

Question 28

What is the role of hydrogen bonds during transcription

Answer 28

Hydrogen bonds break to unwind part of the DNA molecule with the gene to be transcribed; Hydrogen bonds form when free activated RNA nucleotides pair up with complementary DNA bases; The hydrogen bonds break once transcription is completed so the mRNA can be released