Biological molecules - The Role Of Genes

Question 1

Define a gene

Answer 1

A sequence of nucleotide bases which corresponds to a sequence of amino acids

Question 2

What is a sequence of 3 bases called

Answer 2

A triplet (codon in mRNA)

Question 3

What do triplets correspond to

Answer 3

A specific amino acid

Question 4

What happens as codons are read

Answer 4

Polypeptides are made and these form the primary structure of all proteins

Question 5

How can genes be switched on or off

Answer 5

In response to signals that reach the cell and nucleus

Question 6

why must a copy of each gene be transcribed into a length of mRNA

Answer 6

DNA is found in chromosomes and cannot pass out through the nuclear pores

Question 7

where are proteins synthesised

Answer 7

on ribosomes

Question 8

what happens to mRNA after it is made

Answer 8

passes out of the nucleus and moves to a ribosome where it is translated to make a protein

Question 9

what are the characteristics of the genetic code

Answer 9

• universal
• triplet
• degenerate
• non-overlapping

Question 10

what does it mean that the genetic code is degenerate

Answer 10

for all amino acids (except two) there is more than one base triplet

Question 11

how is RNA similar to DNA

Answer 11

• polynucleotide strand with a sugar-phosphate backbone
• the nucleotides contain one of four bases

Question 12

how is RNA different to DNA

Answer 12

• ribose sugar
• single stranded polynucleotide
• uracil replaces thymine

Question 13

what are the three forms of RNA

Answer 13

• mRNA
• rRNA
• tRNA

Question 14

what is mRNA

Answer 14

messenger RNA is made as a complementary strand to a section of DNA. transfers information to ribosome

Question 15

what is rRNA

Answer 15

ribosomal RNA is found in ribosomes. provides the site for protein assembly in the ribosome

Question 16

what is tRNA

Answer 16

transfer RNA carries amino acids to ribosomes

Question 17

Where is mRNA formed

Answer 17

In the nucleus

Question 18

What is the first step of transcription

Answer 18

A section of the DNA unzips (H bonds between base pairs break)

Question 19

What is the second step of transcription

Answer 19

Activated RNA nucleotides form H bonds with exposed complementary bases on template strand in the nucleolus

Question 20

What is the third step of transcription

Answer 20

The enzyme RNA polymerase checks for mistakes and catalyses the formation of phosphodiester bonds between the mRNA nucleotides forming the sugar phosphate backbone

Question 21

What provides the energy for the bonding of adjacent nucleotides

Answer 21

The release of the two extra phosphate groups provides the energy for bonding the adjacent nucleotides

Question 22

What is the fourth step of transcription

Answer 22

At a stop triplet the mRNA breaks off and leaves the nucleus via a nuclear pore

Question 23

What is the fifth step of transcription

Answer 23

In the cytoplasm the mRNA strand attaches to a ribosome

Question 24

Where are ribosomes made and what are they made of

Answer 24

Made in the nucleolus
Made of ribosomal RNA and protein as two subunits

Question 25

Describe ribosomes role in protein synthesis related to its structure

Answer 25

Ribosomes move into the cytoplasm through pores in the nuclear envelope. The two subunits come together to form the ribosome. It has a groove in between where the mRNA is translated into a protein

Question 26

Where is tRNA made

Answer 26

Made in the nucleus and passes into the cytoplasm

Question 27

Describe the structure of tRNA

Answer 27

• a single stranded polynucleotide folded into three hairpin loops
• one free end of unpaired bases joins to a specific amino acid
• at the opposite end there are three unpaired bases called the anticodon
• this briefly joins to the complementary codon on the mRNA

Question 28

What are the triplets of nucleotide bases on mRNA known as

Answer 28

Codons

Question 29

What is the first step of translation

Answer 29

mRNA attaches to ribosomes, either on the RER or free in the cytoplasm
tRNA is in the cytoplasm and has a specific amino acid attached to it

Question 30

What is the second step of translation

Answer 30

tRNA anticodon joins onto the mRNA codon

Question 31

What is the third step of translation

Answer 31

A second tRNA with its specific amino acid joins to the second codon with its complementary anticodon

Question 32

what is the fourth step of translation

Answer 32

a peptide bond forms between the two amino acids and the ribosome moves along. the bond formation requires energy, in the form of ATP.
this continues down the length of the mRNA strand until it reaches a stop codon

Question 33

what is the fifth step of translation

Answer 33

the polypeptide chain can now be arranged into its secondary and tertiary structure

Question 34

what happens to mRNA after translation

Answer 34

after the polypeptide has been assembled, the mRNA can be re used or breaks down and its component pieces recycled.

Question 35

what kinds of mutations could occur

Answer 35

replacement, insertion, deletion

Question 36

what is an insertion an example of

Answer 36

a point mutation

Question 37

describe point mutations

Answer 37

random and spontaneous

Question 38

are mutations always harmful and why

Answer 38

no, lots of genes have their sequences changed and this is what creates alleles