Nucleic Acid and Protein Synthesis

Question 1

What are nucleotides made out of?

Answer 1

1) A nitrogen containing base
2) A pentose sugar
3) A phosphate group

Question 2

What are the nitrogen containing bases in DNA and RNA?

Answer 2

DNA - adenine, guanine, cytosine and thymine
RNA - adenine, guanine, cytosine and uracil

Question 3

Which pentose sugar is present in DNA and RNA?

Answer 3

RNA- ribose sugar
DNA - deoxyribose

Question 4

What is the use of the phosphate group in nucleotides?

Answer 4

Gives the nucleic acids their acidic nature

Question 5

What are purines and which bases are purines?

Answer 5

Adenine and guanine are purines. They have a double ring structure

Question 6

What are pyrimidines and which bases are pyrimidines?

Answer 6

Cytosine, thymine and uracil are pyrimidines. They have a single ring structure

Question 7

Describe the structure of DNA

Answer 7

DNA molecules are made of 2 antiparallel polynucleotide strands. Each strand is made up of alternating sugars and phosphate groups bonded together to form the sugar-phosphate backbone (covalent bonds - phosphodiester bonds). One strand is 3’ to 5’ and the other is 5’ to 3’. The strands are held together by hydrogen bonds between the nitrogenous bases. DNA is described as double helix

Question 8

Complementary base pairing in DNA

Answer 8

Guanine always pairs with cytosine (3 H bonds) and adenine always pairs with thymine (2 H bonds)

Question 9

What is semi-conservative DNA replication?

Answer 9

The process of making an identical copy of a DNA molecule. Half of the original DNA molecule is kept conserved in each of the 2 new DNA molecules

Question 10

Describe the process of DNA replication

Answer 10

The H bonds between the base pairs on the 2 polynucleotide DNA strands are broken (DNA helicase). This unwinds the DNA double helix to form 2 single strands. Each of these strands act as a template for the formation of a new strand. Free nucleotides are attracted to their complementary bases exposed on template strands. DNA polymerase joins together adjacent nucleotides to make the new strand.

Question 11

Details of how DNA polymerase is utilised in DNA replication

Answer 11

Catalyses the condensation reaction between the deoxyribose sugar and phosphate groups of adjacent nucleotides, creating the sugar-phosphate backbone of new DNA strand. H bonds form between complementary base pairs

Question 12

Leading and lagging strand in DNA replication

Answer 12

DNA is unzipped from 3’ to 5’. DNA polymerase works from 5’ to 3’. DNA polymerase synthesises the leading strand continuously. The DNA polymerase enzyme can only synthesise the lagging strand in short segments. DNA ligase is needed to join these lagging strands segments together.

Question 13

Describe the RNA structure

Answer 13

They are made up of a single polynucleotide strand. Each RNA polynucleotide strand is made up of alternating ribose sugar and phosphate groups linked together, with the nitrogenous bases projecting out sideways.

Question 14

What is a gene?

Answer 14

A gene is a sequence of nucleotides that forms part of a DNA molecule

Question 15

What is a polypeptide coded for by

Answer 15

A gene

Question 16

What do the genes in DNA molecules do?

Answer 16

Control protein structure as they determine the exact sequence in which the amino acids join together

Question 17

Describe the principle of the universal genetic code

Answer 17

Different triplets of DNA bases either code for specific amino acids or stop and start codons. These stop and start codons signal where the individual gene stop and start, ensuring that the cell reads the DNA correctly and can produce the correct sequence of amino acids

Question 18

What are the two parts of protein synthesis?

Answer 18

Transcription and translation

Question 19

What happens during transcription?

Answer 19

DNA is transcribed and an mRNA molecule is produced

Question 20

What happens during translation?

Answer 20

mRNA is translated and an amino acid sequence is produced

Question 21

Where does transcription and translation occur?

Answer 21

In the nucleus of the cell and in the cytoplasm of the cell respectively

Question 22

Describe the process of transcription

Answer 22

Part of the DNA molecule unwinds. This exposes the gene to be transcribed. Free RNA nucleotides pair up with their complimentary bases on one strand of part of the unzipped DNA. Sugar-phosphate groups of RNA nucleotides are bonded together by RNA polymerase to form the sugar-phosphate backbone of mRNA. When the gene has been transcribed, the H bonds between mRNA and DNA strands break and the DNA is reformed. The mRNA leaves via pore in nuclear envelope

Question 23

Describe the process of translation

Answer 23

The mRNA molecule attaches to a ribosome. The tRNA molecules bind with their specific amino acid and bring them to the mRNA molecule. The triplet bases on each tRNA molecule pairs with complementary triplet on mRNA. 2 tRNA molecules fit on to the ribosome bringing the amino acid they are bringing side by side. A peptide bond is formed between them. This continues until a stop codon on the mRNA is reached. This amino acid chain then forms a polypeptide

Question 24

What is the transcribed strand?

Answer 24

The strand that is transcribed to from the mRNA molecule

Question 25

Describe the post transcriptional modification in eukaryotic cells

Answer 25

When transcription occurs both exons (coding sequence) and introns (non-coding sequence) are transcribed. As introns are not to be translated, they must be removed. The exons fuse together to form a continuous RNA molecule (mature RNA) that is ready to be translated

Question 26

What is gene mutation?

Answer 26

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

Question 27

How does the insertion of nucleotides affect the polypeptide produced?

Answer 27

An insertion mutation creates a new, different triplet of bases. It has a knock on effect by changing the triplets further on in the DNA sequence. This may dramatically change the amino acids sequence produced from this gene and therefore the ability of the polypeptide to function

Question 28

How does the deletion of nucleotides affect the polypeptide produced?

Answer 28

It has a knock on effect by changing the groups of 3 bases further on in the DNA sequence. This may dramatically change the amino acids sequence produced and therefore the ability of the polypeptide to function

Question 29

How does the substitution of nucleotides affect the polypeptide produced?

Answer 29

The mutation may not alter the amino acid sequence of the polypeptide (silent mutation). The mutation alters a single amino acid in the polypeptide chain (missense mutation). The mutation creates a premature stop codon, causing the polypeptide chain produced to be incomplete and therefore affecting the final protein structure and function (nonsense mutation)