Chapter 8 DNA, genes and protein synthesis

Question 1

what is the definition of a chromosome

Answer 1

A thread like structure that is made of protein and DNA used to pass hereditary information to the next generation

Question 2

What is the definition of a centromere

Answer 2

a centromere joins two chromatids together and attaches to spindle fibres

Question 3

what is the definition of a chromatid

Answer 3

One of the two strands of a chromosome that are joined by a centromere

Question 4

what is the definition of a gene

Answer 4

a section of DNA that codes for a polypeptide or a function RNA

Question 5

what is the definition of an allele

Answer 5

an alternative form of a gene

Question 6

what is the definition of a locus

Answer 6

the position of a gene on a chromosome or a DNA molecule

Question 7

what is the definition of homologous chromosomes

Answer 7

A pair of chromosomes, one maternal and on paternal, that have the same gene loci and determine the same features

Question 8

what is the definition of the genome

Answer 8

The complete set of genes in a cell

Question 9

what is the definition of the proteome

Answer 9

The full range of proteins that the cell can produce

Question 10

What are the differences between DNA in eukaryotes and prokaryotes

Answer 10

Question 11

What are the two types of RNA in proteins synthesis

Answer 11

mRNA (messenger RNA)
tRNA (transfer RNA)

Question 12

What is the function of mRNA
and what is it’s structure

Answer 12

mRNA transfers genetic information from DNA in the nucleus to the ribosomes in the cytoplasm for protein synthesis
It has a single helix structure.

Question 13

What is the function of tRNA and what is its structure

Answer 13

tRNA carries specific amino acids to the ribosomes for protein synthesis
It is a single strand folded into a clover leaf shape, held together by hydrogen bonds between complementary base pairing. it has a specific amino acid attachment site, and a base 3 anticodon

Question 14

Compare DNA, mRNA and tRNA

Answer 14

Question 15

How do you prove that each amino acid is coded for by 3 bases

Answer 15

There are 20 naturally occurring amino acids
There are 4 bases on DNA
1 base coding for 1 amino acid = (4) = 4 amino acids
2 bases coding for 1 amino acid = (44) = 16 possible combinations (not enough)
3 bases coding for 1 amino acid = (44*4) 64 possible combinations (enough)
Therefore, each amino acid is coded for by 3 bases

Question 16

what are the three main features of the genetic code

Answer 16

the genetic code is: universal, non-overlapping and degenerate

Question 17

what does genetic code being universal mean

Answer 17

Each triplet codes for the same amino acid in all species of organisms. This demonstrates evolution from a common ancestor

Question 18

what does genetic code being non-overlapping mean

Answer 18

Each base in a triplet is only read once. Triplets are discrete

Question 19

what does genetic code being degenerate mean

Answer 19

Most amino acids are coded for by more than one triplet.

Question 20

what are introns and exons

Answer 20

Introns - non-coding sections of DNA
Exons - coding sections of DNA

Question 21

What are the effects of a change in the base sequence of amino acids on a protein.

Answer 21

If there is a change in base sequence, this leads toa change in amino acid sequence / primary structure

This leads to a change in hydrogen,ionic, anddisulphide bonds

This alters the tertiary structure of the protein (If the protein is an enzyme, it leads to a change in the shape of the active site so enzyme-substrate complexes cannot form).

Question 22

What are the main features of transcription

Answer 22

• Occurs in the nucleus
• In eukaryotes, pre-mRNA is produced from DNA. This is then spliced to form mRNA
• In prokaryotes, mRNA is produced from DNA

Question 23

What are the stages of trascription

Answer 23

DNA unwinds and DNA helicase breaks H bonds between complementary DNA bases, separating DNA strands and exposing DNA bases

One DNA strand acts as the template strand

Free RNA nucleotides align with the template strand DNA bases by complementary base pairing. A – U, T – A, C – G, G – C

Adjacent RNA nucleotides joined by RNA polymerase (condensation reaction) moving from 5’ to 3’ end

In eukaryotes pre-mRNA is formed. In prokaryotes, mRNA is formed

Question 24

Picture of transcription

Answer 24

Question 25

What is splicing

Answer 25

Transcription forms pre-mRNA from DNA
DNA includes introns and exons

Pre-mRNA therefore contains non-coding introns

Splicing is the removal of introns from pre-mRNA to form mRNA

mRNA now leaves the nucleus through the nuclear pores and attaches to a ribosome in the nucleus

Question 26

diagram for the steps in splicing

Answer 26

Question 27

What are the main features of translation and what is translation

Answer 27

translation is the production of polypeptides from codons on mRNA

Occurs on ribosomes
Involves ribosomes, tRNA, amino acids and ATP

Question 28

what are the stages in translation

Answer 28

1.mRNA attaches to a ribosome
2.Ribosome moves to the start codon (AUG) on the mRNA
3.tRNA brings specific amino acid to the ribosome
4.Anticodon on tRNA binds to thecomplementary codon on mRNA by complementary base pairing
5.Ribosome moves along to next codon. Ribosome can fit two tRNAs on it at a time
6.Process repeated, and amino acids join by condensation reaction with peptide bonds to form polypeptide, using energy from ATP
7. mRNA detaches from the ribosome at the stop codon

Question 29

image for translation

Answer 29