3.4.1 DNA Genes and Protein Synthesis

Question 1

What happens during mRNA splicing?

Answer 1

Introns removed and exons joined, and possibly rearranged, to form mRNA

Question 2

What is an intron?

Answer 2

Non coding sections of DNA

Question 3

What is pre-mRNA?

Answer 3

mRNA strands containing both introns and exons

Question 4

What is an exon?

Answer 4

Coding sections of DNA

Question 5

Describe the process of translation

Answer 5

Ribosome attaches to mRNA. tRNA carries amino acid to ribosome. Complementary base pairing between anticodon on tRNA and codon on mRNA. Hydrogen bonds form between the tRNA and mRNA. A peptide bond forms between amino acids by condensation reaction. The tRNA is released from the ribosome. The ribosome detaches from the polypeptide chain on mRNA when it reaches a stop codon

Question 6

Describe the structure of tRNA

Answer 6

tRNA is folded, has hydrogen bonds holding the structure together, is a fixed size, has an anticodon, has an amino acid binding site

Question 7

How are amino acids joined together to form the 3D structure of a protein?

Answer 7

Peptide bonds between amine group and carboxyl group of another. Primary structure is sequence of amino acids in a protein. The primary structure is folded and held together by bonds to form the secondary and tertiary structures. These bonds are disulphide bonds, ionic bonds, hydrogen bonds and are between the R groups

Question 8

What is mRNA?

Answer 8

Made in the nucleus during transcription, has a codon, carries the genetic code from the DNA in the nucleus to the cytoplasm. Single stranded. Shorter than DNA. Has the sugar ribose (instead of deoxyribose) and the base uracil (instead of thymine) “

Question 9

What is a codon?

Answer 9

Three adjacent bases on mRNA. Each codon contains the information for the addition of a specific amino acid by a ribosome

Question 10

What is tRNA?

Answer 10

Found in cytoplasm, has an amino binding site at one end and an anticodon on the other end, carries amino acids that are used to make proteins to the ribosomes

Question 11

Define the genetic code

Answer 11

The sequence of base triplets in DNA or mRNA which codes for specific amino acids

Question 12

What does it mean by ‘non-overlapping’?

Answer 12

Each base triplet is read in sequence, separate from the triplet before and after it. base triplets do not share their bases

Question 13

Explain the term ‘degenerate’?

Answer 13

There are more possible combinations of triplets than there are amino acids. Some amino acids are coded for by more than one base triplet

Question 14

What are the stop and start codons?

Answer 14

Triplets that tell the cell when to start and stop production of the protein. Found at the beginning and end of the gene

Question 15

What happens when the RNA polymerase attaches to the DNA at the start codon?

Answer 15

The hydrogen bonds between the 2 DNA strands in the gene break, separating the strands and the DNA molecule unwinds

Question 16

What happens when the RNA polymerase lines up free RNA nucleotides alongside the template strand?

Answer 16

Complementary base pairing occurs so that the mRNA strand ends up being a complementary copy of the DNA template strand. RNA polymerase joins the mononucleotides together by phosphodiester bonds in condensation reactions

Question 17

What happens when RNA polymerase reaches a stop codon?

Answer 17

It stops making mRNA and detaches from the DNA. mRNA leaves the nucleus through a nuclear pore and attaches to a ribosome in the cytoplasm

Question 18

What is a gene?

Answer 18

A section of DNA that codes for a polypeptide

Question 19

Define ‘locus’

Answer 19

The particular position that a gene occupues on a chromosome

Question 20

State the 4 features of the genetic code

Answer 20

Triplet, Universal, Non-overlapping and degenerate

Question 21

In eukaryotic cells, what proteins is DNA found wound around?

Answer 21

Histone proteins

Question 22

What’s the difference between chromosomes, chromatids and centromeres?

Answer 22

At the beginning of cell division, each chromosome is visible as two chromatids, joined at the centre by a centromere

Question 23

What’s the difference between a diploid cell and a haploid cell?

Answer 23

A diploid cell contains a full set of chromosomes, a haploid cell contains just half of the homologous pairs (e.g. gamete)

Question 24

Define allele

Answer 24

An allele is a form of a gene

Question 25

What’s the difference between the genome and the proteome?

Answer 25

The genome is the complete set of genes in a cell, the proteome is the complete set of proteins produced by the genome

Question 26

State 2 differences between mRNA and tRNA

Answer 26

tRNA is smaller, clover shaped and more stable than mRNA,

Question 27

Define ‘splicing’

Answer 27

When introns are removed during transcription

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