DNA, genes and protein synthesis

Question 1

gene

Answer 1

Section of DNA that codes for making polypeptides and functional RNA
-Polypeptides make proteins and so genes determine the proteins of an organisms

Question 2

Homologous chromosomes

Answer 2

a pair of chromosomes which contains genes which code for the same characteristics
-different alleles

Question 3

Degenerate code

Answer 3

Each amino acid is coded for by more that one triplet of bases

Question 4

how genes code for
polypeptides

Answer 4

The bases in the gene provide a triplet code
for amino acids.

Three bases is a triplet which provides a code
from one amino acid.

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

The code is non-overlapping, meaning each
base is read once only in a sequence.

Question 5

DNA replicates by semi-conservative replication- explain
this.

Answer 5

DNA replication is semi conservative because each of the new
strands contains one of the original strands

Question 6

allele

Answer 6

Different forms of the same gene, which code for different
polypeptides.

Question 7

Where is a gene located

Answer 7

Locus

Question 8

How is DNA stored in prokaryotic cells

Answer 8

In prokaryotic cells DNA is shorter and forms a circle. It is not associated with proteins, so no chromosomes are present.

Question 9

Describe the structure of a chromosome

Answer 9

The DNA double helix is wound around histones forming a DNA histone complex. This is coiled, and folds to form loops. The loops then coil and pack together to form chromosomes.
DNA is condensed into a single chromosome containing a single molecule of DNA

Question 10

Explain how genes are arranged in a DNA molecule

Answer 10

Each DNA molecule has many genes along its length, and each gene occupies a specific position (the locus) on the DNA molecule.

Question 11

How is DNA stored in Eukaryotic cells

Answer 11

In eukaryotic cells DNA is longer, linear and associated with proteins called histones which enable formation of chromosomes.

Question 12

How is the DNA of mitochondria and chloroplasts similar to DNA of prokaryotic cells

Answer 12

It’s short, circular and not associated with proteins.

Question 13

What are the three features of the genetic code

Answer 13

Universal, degenerate, non-overlapping

Question 14

Genetic code

Answer 14

There must be a minimum of three bases that code for each amino acid

Question 15

Why is it an advantage that the genetic code is degenerate

Answer 15

If a mutation occurs even though the triplet of bases will be different it may still code for the same amino acid and therefore have no effect

Question 16

Universal

Answer 16

The same triplet of bases codes for the same amino acids in all organisms

Question 17

Why is it an advantage that the genetic code is universal

Answer 17

Genetic engineering is possible

Question 18

What are the four bases

Answer 18

Adenine, Guanine, Cytosine and Thymine

Question 19

Non-overlappng

Answer 19

each base in a gene is only part of one triplet of bases that codes for one amino acid

Question 20

What is the advantage of the genetic code being non-overlapping

Answer 20

If a point of mutation occurs, it will only affect one codon and therefore one amino acid.

Question 21

Introns

Answer 21

DNA that do not code for amino acids and therefore polypeptide chains.
-They get removed, spliced, out of mRNA molecules

Question 22

exons

Answer 22

Sections of DNA that do code for amino acids

Question 23

Describe how a gene is a code for the production of a polypeptide.
Do not include information about transcription or translation in your answer.

Answer 23

1. (Because) base/nucleotide sequence;
2. (In) triplet(s);
3. (Determines) order/sequence of amino acid sequence/primary structure (in polypeptide);

Question 24

Not all mutations in the nucleotide sequence of a gene cause a change in the structure of a polypeptide.
Give two reasons why

Answer 24

1.Triplets code for same amino acid/DNA/code/triplets are degenerate
2. Occurs in introns /non-coding sequence;

Question 25

Describe the structure of
ribonucleic acid (RNA)

Answer 25

RNA is made up of nucleotides formed of ribose (a pentose
sugar), organic bases- A, G, C and U (uracil), and a phosphate.

Question 26

Describe the structure of mRNA

Answer 26

-mRNA is a long strand in a single helix.
-It acts as a template for protein synthesis.
-The sequence of bases determines the amino acid sequence.
-Codons provide the codes for individual amino acids.

Question 27

Describe the structure of tRNA

Answer 27

-tRNA is a small molecule made of around 80 nucleotides.
-It is single stranded, but folded into a clover shape. -tRNA molecules bind to specific amino acids.
-It has an anticodon which is
complementary to the codon on the mRNA.

Question 28

Explain how pre-messenger
RNA is produced from DNA
in the process called
transcription

Answer 28

-DNA helicase separates the two strands of the DNA helix by breaking the hydrogen bonds between DNA nucleotides.
-RNA polymerase adds RNA nucleotides which are complementary to the nucleotides of one DNA strand.
-RNA sugar-phosphate backbone forms to form a pre-mRNA strand.

Question 29

Describe how the
pre-messenger RNA is
modified to form mRNA

Answer 29

pre-mRNA undergoes splicing which removes the non-coding sections of mRNA called introns. Introns are removed, exons remain and an mRNA molecules is formed.

Question 30

Explain how a
polypeptide is
synthesised during the
process of translation

Answer 30

A ribosome becomes attached to the mRNA at a start codon.

A tRNA molecule with the complimentary anticodon moves to
the ribosome and pairs with the codon on the mRNA.

The tRNA carries a specific amino acid.

Another tRNA molecule which is complementary to the next
codon on the mRNA brings another amino acid to the
ribosome and peptide bonds form between the amino acids.

The process continues until the ribosome reaches a stop
codon on the mRNA.

The polypeptide chain is complete.

Question 31

Describe the roles of
messenger RNA and
transfer RNA in
translation

Answer 31

mRNA codons are read by the ribosome and a molecule of
tRNA with complementary anticodons bring the specified
amino acids to form the polypeptide chain.

Question 32

Explain how genes code for polypeptides

Answer 32

The bases in the gene provide a triplet code for amino acids.
Three bases is a triplet which provides a code from one amino acid.
Most amino acids are coded for by more than one triplet.
The code is non-overlapping, meaning each base is read once only in a sequence.

Question 33

Genome

Answer 33

all the genetic material within an organism

Question 34

proteome

Answer 34

All the proteins within an organism

Question 35

Anticodon

Answer 35

a sequence of 3 adjacent nucleotides on a molecule of transfer RNA that is complementary to a particular codon on a mRNA molecule.

Question 36

Where does protein synthesis occur

Answer 36

Cytoplasm

Question 37

What is the general function of RNA

Answer 37

To copy and transfer the genetic code from DNA in the nucleus to the ribosomes.

Question 38

What are the 3 types of RNA

Answer 38

mRNA
tRNA
rRNA

Question 39

Describe the function of mRNA

Answer 39

transfers the DNA code from the nucleus to the cytoplasm

Question 40

codon

Answer 40

a sequence of 3 adjacent nucleotides in mRNA that codes for one amino acid.

Question 41

Describe the function of tRNA

Answer 41

-transfer amino acids to the ribosome to create polypeptide chains

Question 42

Describe two differences between the structure of a tRNA molecule and
the structure of an mRNA molecule.

Answer 42

-tRNA is ‘clover leaf shape’, mRNA is linear
-tRNA has anticodon, mRNA has codon