Chapter 8 - DNA, genes and protein synthesis

Question 1

What is a gene?

Answer 1

A gene is a sequence of DNA bases that code for either a polypeptide or RNA

Question 2

How are genes involved in making proteins?

Answer 2

The order of DNA bases on a gene determines the order of amino acids in a particular polypeptide. This polypeptide then determines the primary structure of a protein

Question 3

How many bases code for one amino acid?

Answer 3

Three

Question 4

What is functional RNA?

Answer 4

RNA molecules, other than mRNA that perform special tasks during protein synthesis

Question 5

*What is a cell’s genome?

Answer 5

The complete set of genes in a cell

Question 6

*What is a cell’s proteome?

Answer 6

The full range of proteins a cell is able to produce

Question 7

What are most amino acids coded by?

Answer 7

Between two and six triplets

Question 8

What will all chains of amino acids start with?

Answer 8

Methionine - the start codon

Question 9

What will all chains of amino acids include?

Answer 9

A stop codon

Question 10

What does the term ‘non-overlapping’ mean?

Answer 10

Each base is read only once

Question 11

What are introns?

Answer 11

Non-coding parts of DNA

Question 12

What is a DNA molecule in a prokaryotic cell like?

Answer 12

The DNA molecules are carried as chromosomes, but are shorter and circular. The DNA supercoils to fit in the cell

Question 13

What is eukaryotic DNA like?

Answer 13

It is a linear molecule that exists as chromosomes. The DNA molecule is so long that it must be would around proteins, called histones, to fit in the nucleus. This creates compact chromosomes

Question 14

Which organelles in eukaryotic cells also have their own DNA?

Answer 14

Mitochondria and chloroplasts, but it is circular and shorter than other DNA in the nucleus

Question 15

What are homologous pairs?

Answer 15

Pairs of matching chromosomes, which are the same size and have the same genes

Question 16

*What are alleles?

Answer 16

Different forms of genes

Question 17

What is the diploid number?

Answer 17

The total number of chromosomes in an organism

Question 18

How do alleles differ?

Answer 18

They contain different base sequences so code for different proteins, which create different versions of the same polypeptide.

Question 19

What are exons?

Answer 19

Sections of genes that code for amino acids

Question 20

What are non-coding repeats?

Answer 20

Sections of DNA that are repeating (e.g. CTTCTTCTT) but don’t code for amino acids

Question 21

How many different amino acids are there?

Answer 21

20

Question 22

Why is DNA degenerate?

Answer 22

Most amino acids are coded for by more than one triplet

Question 23

Why is the genetic code described as universal?

Answer 23

The same triplet codes for the same amino acid in all living organisms

Question 24

How do you get the mRNA sequence from a DNA sequence?

Answer 24

You use the complimentary base pairs, but always switch T for U

Question 25

What does T stand for?

Answer 25

Thymine

Question 26

What does A stand for?

Answer 26

Adenine

Question 27

What does G stand for?

Answer 27

Guanine

Question 28

What does U stand for?

Answer 28

Uracil

Question 29

What does C stand for?

Answer 29

Cytosine

Question 30

What is a codon?

Answer 30

A triplet of bases that code for one amino acid

Question 31

How do you work out tRNA from mRNA?

Answer 31

The complementary pairs (tRNA contains uracil, not thymine)

Question 32

How do you work out the sequence of amino acids from a section of mRNA?

Answer 32

Break it down into codons and use information in the table provided

Question 33

How are di-nucleotides formed?

Answer 33

Two nucleotides join together in a condensation reaction between the sugar on one nucleotide and the phosphate on another

Question 34

What bond is formed in polynucleotides?

Answer 34

Phosphodiester

Question 35

What are the purine bases?

Answer 35

Guanine and adenine

Question 36

What are the pyrimidine bases?

Answer 36

Thymine, uracil and cytosine

Question 37

What is RNA made from?

Answer 37

A single polynucleotide strand in which each nucleotide is made from a ribose sugar, a base (A, C, G, U) and a phosphate group

Question 38

Function of mRNA

Answer 38

After it is formed through transcription, it exits the nucleus through nuclear pores, where it travels to the ribosome. It acts as a template for protein synthesis

Question 39

Structure of tRNA

Answer 39

A single-stranded molecule which is folded into a clover leaf shape, held in place by strong hydrogen bonds between complementary bases. At one end, there is an anticodon, which is complementary to the triplet on the mRNA, and at the other there is an amino acid bonding site

Question 40

Function of tRNA

Answer 40

It carries amino acids used to make proteins to the ribosome

Question 41

What is transcription?

Answer 41

The formation of pre-mRNA from DNA through complementary base pairing

Question 42

What is translation?

Answer 42

mRNA and tRNA are used to convert the genetic code into the polypeptide chains needed to form proteins

Question 43

Process of transcription

Answer 43

DNA helicase breaks the hydrogen bonds between nucleotides This causes the double helix to unravel One of the strands acts as a template strand. Using this, RNA polymerase attaches complementary nucleotides from the cytoplasm to the exposed strand As the polymerase moves through the molecule and assembles the pre-mRNA, the double helix rejoins behind it and hydrogen bonds reform When the polymerase reaches a stop codon, it stops and detaches

Question 44

Why doesn't pre-mRNA need to be spliced in prokaryotes?

Answer 44

There are no introns in prokaryotes' DNA

Question 45

How are introns removed from eukaryotic DNA?

Answer 45

Splicing

Question 46

What happens to pre-mRNA to make mRNA?

Answer 46

It is spliced - introns are removed and exons are joined together

Question 47

What happens to a polypeptide chain after it has been made?

Answer 47

It is coiled to form the secondary structure The secondary structure is coiled to form the tertiary structure Different polypeptide chains are linked to form the quaternary structure

Question 48

Process of translation

Answer 48

A ribosome becomes attached to the mRNA A tRNA molecule, carrying an amino acid, with a complementary anticodon to the codon on the mRNA sequence attaches itself to the mRNA by complementary base pairing A second tRNA molecule attaches to the mRNA in the same way The two amino acids attached to the tRNA molecules join together with a peptide bond The first tRNA molecule moves away, leaving the amino acid behind A third tRNA molecule attaches to the mRNA By the same process, its amino acid joins to the two amino acids already there The second tRNA molecule moves away This continues until the stop codon is reached. The polypeptide chain moves away from the ribosome; translation is complete

Question 49

What differs between amino acids?

Answer 49

The 'R' group

Question 50

Do tRNA molecules have hydrogen bonds?

Answer 50

Yes

Question 51

Which molecules are made from a single polypeptide strand?

Answer 51

mRNA and tRNA