3.4.2 DNA and protein synthesis

Question 1

Define genome

Answer 1

complete set of genes in the cell

Question 2

Define proteome

Answer 2

The full range of proteins that a cell can make

Question 3

Define codon

Answer 3

Three bases on mRNA that code for an amino acid

Question 4

Define anti-codon

Answer 4

Three bases on tRNA that are complementary to the codon on mRNA

Question 5

Name the process that removes base sequences from pre-mRNA to form mRNA.

Answer 5

Splicing

Question 6

Give some ways in which the structure of an mRNA molecule is different from the structure of a tRNA molecule.

Answer 6

• mRNA is a single helix where as tRNA is a clover shaped molecule
• mRNA do not contain hydrogen bond where as tRNA do
• mRNA do not have base pairing where as tRNA do
• mRNA has codons where as tRNA has anti-codons
• mRNA don’t have an amino acid binding site where as tRNA do

Question 7

Explain the difference between pre-mRNA and mRNA.

Answer 7

1. Pre-mRNA contains introns where as mRNA contains only exons;
2. mRNA has undergone splicing, pre-mRNA has not.

Question 8

What is the role of RNA polymerase during transcription?

Answer 8

To join RNA nucleotides together (by forming phosphodiester bonds) to form mRNA

Question 9

Name the three steps involved in protein synthesis

Answer 9

Transcription
Splicing
Translation

Question 10

Describe how mRNA is produced in the nucleus of a cell.

Answer 10

1. DNA helicase breaks the hydrogen bonds holding complementary base pairs
2. One DNA strand acts as a template
3. Free RNA nucleotides are attracted to DNA template strand.
4. RNA nucleotides bind to their complementary base pair on the template strand - A>U; C>G
5. RNA polymerase joins RNA nucleotides together
6. Pre-mRNA is spliced to remove the introns

Question 11

Explain the role of the anticodon in protein synthesis.

Answer 11

Anticodons on the tRNA bind to codons on the mRNA
Anticodons are complementary to those on the codon
So the correct amino acid is brought to the ribosome

Question 12

Name the organelle involved in translation.

Answer 12

Ribosomes

Question 13

Describe the role of tRNA in the process of translation.

Answer 13

1. Anticodons on tRNA are complementary to specific codons on mRNA
2. A specific amino acid is bound to the tRNA
3. This amino acid is carried to the ribosome
4. Ribosome moves along mRNA.
5. Peptide bond forms between adjacent amino acids.
6. Via condensation reaction
7. Requires ATP.
8. Ribosome detaches from mRNA when STOP codon reached.

Question 14

Starting with mRNA, describe how the process of translation leads to the production of a polypeptide.

Answer 14

1. The mRNA attaches to a ribosome
2. Anticodons on tRNA are complementary to specific 3. codons on mRNA
3. A specific amino acid is bound to the tRNA
4. This amino acid is carried to the ribosome
5. Ribosome moves along mRNA.
6. Peptide bond forms between adjacent amino acids.
7. Via condensation reaction
8. Requires ATP.
9. Ribosome detaches from mRNA when STOP codon reached.

Question 15

What is a histone?

Answer 15

A protein that DNA forms a complex with to allow it to be condensed into a chromosome.

Question 16

When chromosomes become visible at the start of cell division, they appear as 2 threads joined at a central point called a…

Answer 16

centromere

Question 17

The 2 condensed ‘threads’ of DNA that are joined at a centromere and make up a chromosome are called…

Answer 17

sister chromatids

Question 18

Describe how DNA is packed into a chromosome.

Answer 18

1. DNA molecule combines with histones.
2. DNA-Histone complex begins to coil and fold to form loops.
3. Loops coil further and pack together to form the chromosome.

Question 19

What is meant by homologous chromosomes?

Answer 19

1. A pair of corresponding maternal and paternal chromosomes.
2. Their genes (are the same) are at the same loci so they determine the same characteristics.

Question 20

The total number of maternal AND paternal chromosomes in an organism is called its…

Answer 20

diploid number

Question 21

If a tRNA is involved what stage of protein synthesis are we looking at?

Answer 21

translation

Question 22

what shape does a tRNA have?

Answer 22

clover shape

Question 23

The codon on mRNA is AUG - what will be the complementary DNA and anti-codon?

Answer 23

DNA - TAC

anti-codon - UAC

Question 24

How do new alleles come about?

Answer 24

1. Random mutations alter coding sequences.
2. This leads to changes in the amino acid sequence.
3. This leads to a different polypeptide with a possibly different function/non-functional.

Question 25

Do homologous chromosomes carry the same alleles (version of genes)?

Answer 25

No - they do carry same genes

Question 26

Define allele.

Answer 26

A version of a gene e.g. blue and brown versions of the eye colour gene.

Question 27

How do new alleles come about?

Answer 27

1. Random mutations alter coding sequences. 2. This leads to changes in the amino acid sequence. 3. This leads to a different polypeptide with a possibly different function/non-functional.

Question 28

How are DNA nucleotides different to RNA nucleotides?

Answer 28

DNA has thymine RNA has uracil | DNA has deoxyribose RNA has ribose

Question 29

How is mRNA structure different to tRNA?

Answer 29

mRNA longer mRNA straight - tRNA clover shape mRNA has no paired bases/no hydrogen bonds

Question 30

Describe how mRNA is made in the nucleus

Answer 30

1. Helicase; 2. Breaks hydrogen bonds; 3. Only one DNA strand acts as template; 4. RNA nucleotides attracted to exposed bases; 5. (Attraction) according to complemtary base pairing rule (AU, GC, TA, CG); 6. RNA polymerase joins (RNA) nucleotides together; 7. Pre-mRNA formed and is spliced to remove introns 8. forming mRNA;

Question 31

name the 3 bases in mRNA that codes for a specific amino acid

Answer 31

codon

Question 32

Describe the role of the ribosome in the production of a polypeptide

Answer 32

mRNA binds to ribosome two codon binding sites tRNA with specific anticodon bind to codon formation of a peptide bond in ribosome between amino acids ribosome moves along mRNA

Question 33

The base sequence of mRNA maybe different the sequence of pre-mRNA in eukaryotic cells

Answer 33

introns in pre mRNA splicing removes these introns so only exons present in mRNA

Question 34

define degenerate

Answer 34

more than one codon codes for a single amino acid

Question 35

describe how mRNA differs to tRNA

Answer 35

1. mRNA has no H bonds tRNA does 2. mRNA has codon, tRNA has anticodon 3. mRNA is longer 4. mRNA linear, tRNA clover shaped 5. mRNA has no AA binding site, tRNA does

Question 36

Describe translation

Answer 36

1. mRNA binds to ribosome 2. ribosomes moves to START codon (AUG) 3. 2 codons fit in the ribosome 4. first tRNA enters carrying specific AA 5. anticodon binds to mRNA codon 6. second tRNA enters - 2 tRNA binding sites 7. AA join by peptide bond using ATP 8. ribosome moves along to next codon to read