3.4.1 DNA, Genes And Chromosomes, 3.4.2 DNA and protein synthesis

Question 1

Structure of DNA in prokaryotes

Answer 1

Short and circular and not wrapped around proteins.

Question 2

Structure of DNA in eukaryotes (nucleus)

Answer 2

Very long, linear and wrapped around hisones (a protein)

Question 3

What is a chromosome formed from?

Answer 3

DNA molecule and its associated proteins

Question 4

What is a gene?

Answer 4

A specific base sequence of DNA that codes for the amino acid sequence of a polypeptide and functional RNA

Question 5

Position of gene

Answer 5

Occupies a fixed position (locus) on a particular DNA molecule

Question 6

What is a triplet code?

Answer 6

A sequence of 3 DNA bases that codes for a specific amino acid.

Question 7

coding sequences

Answer 7

Regions of the DNA which code for a particular protein or functional RNA
e.g ribosomal RNA , tRNA

Question 8

Non-coding sequences

Answer 8

DNA regions which do not code for anything

Question 9

Exons

Answer 9

Sequence that codes for amino acid sequences

Question 10

Introns

Answer 10

Non coding sequences

Question 11

What is a Codon?

Answer 11

Each section of the gene which codes for a different amino acid.
e.g. (GCU) codon 1
Each codon encodes a specific amino acid
Non overlapping

Question 12

Genetic code

Answer 12

Universal
Non-overlapping
Degenerate

Question 13

What is meant by the genetic code being degenerate?

Answer 13

multiple codons encode a single amino acid

Question 14

DNA in mitochondria and chloroplasts

Answer 14

similar to prokaryotes

• ahort
• circular
• not wrapped around histones

Question 15

What is a histone?

Answer 15

DNA binding proteins. Strands of DNA wrap around it to form ‘nucleosome’

Question 16

What is a chain of nucleosomes called?

Answer 16

Chromatin (type of amino acid)

Wound up to form a single chromosome

Question 17

What are chromatins used for?

Answer 17

to make proteins

Question 18

much of the nuclear DNA code for polypeptides (T/F)

and why?

Answer 18

False
most of the nuclear DNA doesnt code for a polypeptide
e.g. there are non-coding multiple repeats of base sequences between genes.

Question 19

Protein synthesis overview

Answer 19

DNA
DNA template strand
transcription
mRNA
Translation
Protein

Question 20

How many chromosomes are there

Answer 20

23 pairs, 46 single in total

Question 21

homologous chromosomes (definition)

Answer 21

Both carry the same genes

Paternal and maternal chromosome pair

Question 22

What is an alelle?

Answer 22

Different forms of the same gene

Question 23

Start codon

Answer 23

Found at 5’ end of gene(ATG)

Question 24

Stop codon

Answer 24

Found at 3’ end (TAA, TAG, TGA)

Question 25

Cell genome

Answer 25

Complete set of genes in the cell

Question 26

Cell proteome

Answer 26

Full range of proteins the cell can produce

Question 27

mRNA (in protein synthesis)

Answer 27

Produced in nucleus during transcription
Single stranded
UACG bases

Question 28

tRNA (in protein synthesis)

Answer 28

Carries and transfers amino acids during protein synthesis, brings amino acid to ribosomes
Bring correct amino acid relating to codons on the mRNA

Question 29

rRNA (in protein synthesis)

Answer 29

combines with specialised proteins to form ribosomes
Carry out protein synthesis
Interface for the mRNA and tRNA to interact and catalyse the condensation reaction to form peptides

Question 30

Transcription definition

Answer 30

Production of mRNA from DNA. RNA polymerase joins the mRNA nucleotides

Question 31

Protein synthesis definition

Answer 31

Process by which the DNA base sequence in genes is used to make polypeptides
(Occurs in ribosome

Question 32

Transcription in prokaryotes

Answer 32

Results directly in the production of mRNA from DNA

Question 33

Transcription in eukaryotes

Answer 33

Results in the production of pre-mRNA which is then spliced to form mRNA

Question 34

Transcription process

Answer 34

1) RNA polymerase attatches to the DNA double helix at beginning of a gene
2) H-bonds between DNA strands break, exposing bases
3) one strand used as template
4) RNA polymerase lines up free nucleotides alongside exposed bases. Specific base pairing takes place (T replaced by U)
5) Joined together by RNA polymerase to form mRNA molecule.
6) RNA polymerase moves along DNA, seperating the strands
7) H-bonds between DNA strands form again and form double helix. Left with a single mRNA strand
8) mRNA moves out nucleus through nuclear pore (in eukaryotes) and attatches to a ribosome in the cytoplasm.

Question 35

Translation process

Answer 35

1) mRNA attaches to ribosome and tRNA molecules carry amino acids to it. (ATP energy- for bond betweenamino acid and tRNA to form)
2) tRNA with anticodon complimentary to first codon on mRNA attaches itself to mRNA by specific base pairing.
3) 2nd tRNA attaches in same way
4) two amino acids attached to tRNA are joined by peptide bonds
5) 3rd attaches and first moves away
6) process continues until a stop signal is reached
7) polypeptide chain moves away and forms a protein

Question 36

Primary structure of protein

Answer 36

determined by the sequence of amino acids and determines the tertiary structure of protein

Question 37

DNA indirectly codes for:

Answer 37

Shape of proteins - for specific function