Topic 2B - Proteins and Genetics

Question 1

Describe primary structure of a protein

Answer 1

two amino acids are bonded together with a peptide bond and joined by a condensation reaction

Question 2

Describe secondary structure of a protein

Answer 2

• bonded by hydrogen bonds.

- alpha helix caused by coils in chains and beta pleated sheets are caused by folds in the chains

Question 3

Describe tertiary structure of a protein

Answer 3

• Disulphide, ionic or hydrogen bonds form

- R groups form

Question 4

Describe globular proteins

Answer 4

• are compact and spherical

- they are soluble

Question 5

Describe fibrous proteins

Answer 5

• fibrous proteins are long chains that are strong and cross-linked
• they are insoluble.

Question 6

EQ. State 3 structural differences between DNA amd RNA (3 marks)

Answer 6

• DNA has the pentose sugar deoxyribose while RNA ribose
• DNA has the base thymine while RNA has uracil
• DNA is double stranded while RNA is single stranded

Question 7

EQ. State what is meant by the term template for the synthesis of messenger RNA. (1 mark)

Answer 7

The free floating RNA nucelotides attach to this strand

Question 8

EQ. Analysis of a sample of DNA found that 40% of the nucleotides contained cytosine. In the same sample of DNA the percentage of nucleotides containing adenine would be… (1 mark)

Answer 8

10%

Question 9

EQ. Describe three differences between the processes of replication and transcription
of DNA. (3 marks)

Answer 9

• replication uses DNA nucelotides while transcription uses RNA nucelotides
• replication uses DNA polymerase while transription ues RNA polymerase
• in replication both strands are copied while in transription only one strand is copied
• replication results in double stranded DNA while trancription results in a single strand of mRNA

Question 10

EQ. Individual mononucleotides in a molecule of mRNA are joined together by… (1 mark)

Answer 10

phosphodiester bonds

Question 11

EQ. Describe the structure of a mononucleotide found in RNA. (2 marks)

Answer 11

• it contains ribose and phosphate

- conatins the base uracil, guanine, adenine and cytosine

Question 12

EQ. Describe the process of protein synthesis that occurs in the cytoplasm. (5 marks)

Answer 12

• mRNA attaches to the ribosome
• each tRNA molecule carries an amino acid
• complementry base pairing occurs between the mRNA and tRNA
• hydrogen bonds form between the tRNA and mRNA strands
• peptide bonds form between the adjacent amino acids

Question 13

EQ. Phenylketonuria is the result of a gene mutation.
People with phenylketonuria cannot convert phenylalanine to tyrosine. Explain why people with this gene mutation cannot convert phenylalanine to tyrosine. (4 marks)

Answer 13

• if theres a change in the DNA sequence
• the amino acid sequence changes
• this would lead to different R groups
• and different types of bonding would form
• this would change the shape of the active site

Question 14

EQ. Explain how the expression of a gene mutation in a person with cystic fibrosis causes a build-up of mucus in their respiratory system. (5 marks)

Answer 14

• the gene mutation changes the primary structure
• the CFTR channel protein is non-functional
• cholride ions cannot move out of the cell
• this draws water into the cells from the mucus by osmosis
• this causes the mucus to become thicker
• the thick mucus cannot be moved by the clila which causes coughing

Question 15

EQ. Explain the nature of the genetic code. (2 marks)

Answer 15

• degenerate

- non-overlapping

Question 16

Explain how the genetic code is non-overlapping.

Answer 16

Base triplets don’t share their bases. They are read seperately.

Question 17

Explain how the genetic code is degenerate.

Answer 17

Each amino acid is coded for by more than 1 base triplet.

Question 18

EQ. Describe the process of DNA replication. (5 marks)

Answer 18

• it is semi-conservative replication
• hydrogen bonds break and the DNA molecule unwinds
• mononucleotides line up against both strands
• complementry base pairing occurs between both strands
• hydrogen bonds form between the bases
• via a condensation reaction
• catalysed by DNA polymerase

Question 19

EQ. State what is meant by the term gene. (2 marks)

Answer 19

• sequence of bases in DNA

- sequence of base triplets code for amino acids

Question 20

EQ. Describe the role of tRNA in the production of leptin, a protein. (3 mark)

Answer 20

• tRNA carries an amino acid to the ribosome
• each tRNA molecule carries a single amino acid
• anticodon on the tRNA chain bind to the complementary codon on the mRNA

Question 21

EQ. Describe how the primary structure of leptin, a protein, enables it to be soluble in water. (3 marks)

Answer 21

• protein must have a globular structure
• the primary structure determines the tertiary structure
• the globular structure has hydrophobic groups on the inside of the protein and hydrophilic groups on the outside
• water forms hydrogen bonds with protein

Question 22

EQ. State the type of chemical reaction catalysed by trypsin, which specifically acts on a polypeptide to form amino acids. (1 marks)

Answer 22

hydrolysis, in the first bit of transcription

Question 23

State how enzymes work

Answer 23

by decreasing the activation energy of a reaction