6. Nucleic Acids And Protein Synthesis

Question 1

Describe the structure of nucleotides

Answer 1

Made up of:
A nitrogen-containing base
A pentose sugar
A phosphate group.

Question 2

What are the bases found in DNA?

Answer 2

Adenine
Guanine
Thymine
Cytosine

Question 3

What are the bases found in RNA?

Answer 3

Adenine
Guanine
Uracil
Cytosine

Question 4

Which bases are referred to as purines and what is their structure?

Answer 4

Adenine and guanine
It has two rings in its structure

Question 5

Which bases are referred to as pyrimidines and what is their structure?

Answer 5

Thymine
Cytosine
Uracil
It has one ring in its structure

Question 6

Describe the structure of Adenosine Triphosphate (ATP)

Answer 6

Consists of:
Adenine
Ribose
Phosphate

Question 7

What is a dinucleotide?

Answer 7

Two nucleotides joined together by a phosphodiester bond.

Question 8

What are the 7 features of the DNA molecule?

Answer 8

1. It is made of two polynucleotide chains
2. Each chain is a right handed helix
3. The two chains coil around each other to form a double helix
4. The chains are antiparallel- they run in opposite directions.
5. Each chain has a sugar phosphate backbone with bases projecting at right angles
6. There are hydrogen bonds between the bases of the two opposite chains
7. Base pairing is always: A and T, G and C

Question 9

How many hydrogen bonds are between each base pair?

Answer 9

A links with T by two hydrogen bonds
G links with C by three hydrogen bonds

Question 10

Describe the replication process of DNA.

Answer 10

-Starts by the unwinding of the two strands of DNA by the breaking of the hydrogen bonds
-The enzyme DNA polymerase is then used for the copying process; a molecule of this enzyme attaches to each of the single strands and adds a new nucleotide at a time, which is held by hydrogen bonding to the strand being copied.
-DNA polymerase follows the unwinding process copying the DNA as it is unwound the new strand is called the leading strand.
-For the bottom parent strand, the 5’ to 3’ direction of copying is in the opposite direction to the unwinding.
The new strand being formed is called the lagging strand

Question 11

What does DNA ligase do?

Answer 11

Its job is to connect all the new nucleotides with covalent bonds. DNA ligase connects neighboring nucleotides with phosphodiester bonds to form the sugar-phosphate backbone of the new DNA molecule.
Before this they are only holding on to the parent strand with hydrogen bonds between complementary bases.

Question 12

Why is DNA copying referred to as semi-conservative replication?

Answer 12

Each time a DNA molecule is replicated, half the original molecule is kept in each of the new molecules

Question 13

What are the 4 features of a genetic code?

Answer 13

-it is a three letter code
-the code is universal meaning that each triplet codes for the same amino acid in all living things.
-the code has punctuations, three iv the DNA triplets act as ‘full stops’ in the message.
-the code is describes as redundant or degenerate, meaning that some amino acids are coded for by more than one triplet.

Question 14

What is transcription?

Answer 14

The process by which DNA makes mRNA

Question 15

What is translation?

Answer 15

The process by which a sequence of bases in mRNA is converted into a sequence of amino acids in a polypeptide

Question 16

Where does transcription take place?

Answer 16

In the nucleus

Question 17

The enzyme responsible for transcription is called……

Answer 17

RNA Polymerase

Question 18

Explain the process of transcription.

Answer 18

RNA polymerase attaches to the beginning of the gene to be copied. It starts to unwind the DNA of the gene and another enzyme breaks the hydrogen bonds between the two strands and this creates two single-stranded sections of DNA with the normal double helical structure either side of the unzipped section. Only one of the exposed strands is copied, this is the template or transcribed strand. The other strand is called the non-transcribed strand.

Question 19

Explain the process of Splicing.

Answer 19

Splicing is the removal of sections of the primary transcript. The sections removed are called introns and the nucleotide sequences that remain after the introns are removed are called exons.

Question 20

What is the function of introns in the DNA?

Answer 20

They can help to regulate the activity of genes.

Question 21

What is a codon?

Answer 21

Sequence of three bases on an mRNA molecule that codes for a specific amino acid or for a stop signal.

Question 22

What is the other type of RNA involved in translation and what does it do?

Answer 22

tRNA. Transfer RNA
Its job is to transfer amino acids to the ribosome.

Question 23

What is an anticodon?

Answer 23

Sequence of three unpaired bases on a tRNA molecule that binds with a codon in mRNA

Question 24

describe the process of translation.

Answer 24

1. The tRNA with the anticodon complimentary to the first codon on the mRNA enters the ribosome and attaches to the codon by H bonding.
2. The second tRNA enters the ribosome as two can fit into the ribosome at any one time.
3. The amino acids carried by the two tRNAs are now side by side and a peptide bond is formed between them
4. The first tRNA now leaves the ribosome clicks forward one codon and the third tRNA enters with the next amino acid.
   This process is repeated until a stop codon is reached

Question 25

What is a mutation?

Answer 25

A random change in the structure of DNA.

Question 26

Explain how a mutation occurs.

Answer 26

A mutation occurs when a wrong nucleotide is inserted and this may be because of errors during DNA replication or because damage is done to the DNA by factors such as radiation or carcinogens

Question 27

Why is a mutation harmful?

Answer 27

Making a random change in the amino acid sequence of a polypeptide is likely to be harmful and this may affect the way the polypeptide folds up and in turn change the tertiary structure of the protein. This could affect the functioning of the polypeptide

Question 28

What are the three types of mutation?

Answer 28

1. Substitution- a base is replaced by a different base
2. Deletion- a base is lost and not replaced
3. Insertion- a base is added

Question 29

What is a frame- shift mutation?

Answer 29

A type of gene mutation caused by insertion or deletion of one or more nucleotides resulting in incorrect reading of the sequence of triplets in the genetic code due to a shift in the reading frame.