Topic 4 - A: DNA, RNA and protein synthesis

Question 1

DNA in a eukaryotic cell

Answer 1

Long molecules of DNA
Wound around histone proteins
The DNA and protein is wound very tightly to form chromosomes

Question 2

DNA in a prokaryotic cell

Answer 2

Short and circular molecules of DNA
DNA not wound around Histone proteins
Supercoils to fit in cell

Question 3

Define Gene

Answer 3

A sequence of DNA bases that codes for RNA

The sequence of Amino acids in a polypeptide forms the primary structure of protein

Question 4

What’s the difference between exons and introns

Answer 4

Introns are removed in protein synthesis to not interrupt the amino acid sequence and exons remain.

Question 5

Define Allelle

Answer 5

Alternative form of a gene coding for a different versions of same polypeptide

Question 6

What is RNA

Answer 6

Single polynucleotide chain containing Uracil instead of Thymine

Question 7

What is mRNA

Answer 7

Made during transcription
Used to make a protein during translation
Single polynucleotide strand
Three groups of adjacent bases are called codons

Question 8

What is tRNA

Answer 8

Translation
Carries three amino acid used to make proteins to the ribosomes
Single polypeptide chain folded into a clover shape
Hydrogen bonds to hold in shape
Specific sequence of three bases at one end called an anticodon
Amino acid binding site at other end

Question 9

Describe transcription

Answer 9

1) RNA polymerase attaches to DNA, DNA helicase which is attached to RNA polymerase breaks the hydrogen bonds between the two DNA strands
This separates the strands, one of which is used as a template to make an mRNA copy
2) RNA polymerase lines up the free RNA bases alongside exposed bases on template strand. As they are a specific complementary base pairing they are a complementary copy of the DNA template strand.
3)RNA polymerase moves down the DNA creating hydrogen bonds between uncoiled strands of DNA
4) RNA polymerase reaches a stop signal meaning it stops making mRNA adn detaches from DNA

Question 10

What is pre-mRNA

Answer 10

mRNA strands containing introns and exons

Question 11

What occurs in splicing

Answer 11

introns removed
exons come together
takes place in the nucleus

Question 12

Translation

Answer 12

occurs in ribosomes in cytoplasm
amino acids are joined together to make a polypeptide chain (protein)

1) mRNA attaches to a ribosome, tRNA molecule carry amino acids to it. ATP provides the energy for the bond between tRNA and amino acid
2)tRNA molecule with anticodon that’s complementary to first codon attaches to mRNA by complementary base pairing. Another tRNA molecule attaches to next codon on mRNA in the same way.
3)These two amino acids that are attached to the tRNA are joined by peptide bond. The first tRNA molecule moves away leaving an amino acid. Then a third tRNA molecule binds to the next codon on the mRNA, then the amino acids bond by peptide bond and the tRNA moves away. This is continued until they reach a stop signal.
The polypeptide chain then moves away from ribosome and translation is complete.