4.1-2 DNA and Protein Synthesis

Question 1

Features of DNA in a eukaryotic cell?

Answer 1

Found in the nucleus 
In a linear shape
In the form of chromosomes 
Wrapped around proteins called histones
Long DNA molecule

Question 2

Features of DNA in a prokaryotic cell?

Answer 2

Found loose in the cytoplasm
In a circular loop form
Shorter DNA molecule

Question 3

Other than the nucleus where else is DNA found in eukaryotic cells?

Answer 3

Mitochondria

Chloroplasts

Question 4

How is the mitochondrial and chloroplast DNA thought to have got there?

Answer 4

Endosymbiotic theory

The organelles may have been engulfed and then kept to be used

Question 5

How is DNA formed into a chromosome?

Answer 5

The DNA double helix is wrapped around histone proteins creating nucleosome fibre
The nucleosome fibre is coiled around to form chromatin fibre
The chromatin fibre is looped in a figure of 8 shape and 6 loops form a rosette
30 rosettes make a coil and there are 10 coils in each chromatid

Question 6

Why is DNA stored in a chromosome like it is?

Answer 6

So you can have a lot of DNA in a small space

It is easy to separate the DNA without damage

Question 7

What is a gene?

Answer 7

Part of the length of a DNA molecule that codes for 1 polypeptide

Question 8

What is different about DNA?

Answer 8

Not all of it codes for proteins

Question 9

What is DNA made up of?

Answer 9

Introns and exons

Question 10

What are introns?

Answer 10

Non-coding DNA which can be found between genes in multiple repeats or within a gene

Question 11

What are exons?

Answer 11

Sequence of bases in a gene that code for a sequence of amino acids in a protein

Question 12

What is your genome?

Answer 12

The full set of genes in a cell

Question 13

What is your proteome?

Answer 13

The full range of proteins coded for by the genes

Question 14

What is your karyotype?

Answer 14

It is the number and appearance of chromosomes in the nucleus of a eukaryotic cell

Question 15

What is an allele?

Answer 15

A version of a gene

Question 16

What are some key features of DNA that allows it to code effectively for a polypeptide?

Answer 16

Universal code
1 codon = 1 amino acid
Degenerate code
Non-overlapping

Question 17

What is a universal code?

Answer 17

DNA is used in virtually all organisms as the material of inheritance

Question 18

What is a codon?

Answer 18

It is made up of 3 bases

3 bases = 1 codon = 1 amino acid

Question 19

What is a degenerate code? Use?

Answer 19

The amino acids can be coded for by more than one codon

Combats the substitution mutations in the third base as it has very little affect on the polypeptide being made

Question 20

How does non-overlapping make DNA effective in production of polypeptides?

Answer 20

Each base in the sequence is read only once

Question 21

What are the stages of protein synthesis?

Answer 21

Transcription

Translation

Question 22

Where does transcription take place?

Answer 22

In the nucleus

Question 24

What is DNA and pre mRNA made up of?

Answer 24

Introns

Exons

Question 25

What are introns and exons? How to remember?

Answer 25

Exons contain the genetic information that codes for a protein
Introns are sequences that are not used to make the final protein

Introns - In the bin
Exons - Expressed

Question 26

What happens to convert pre mRNA to mRNA?

Answer 26

Introns are removed and Exons are spliced together

Question 28

What are the stages of transcription?

Answer 28

DNA that forms the gene is unzipped to form two separate strands using DNA helicase
Free RNA nucleotides aline to their corresponding base pairs on the template strand forming hydrogen bonds
RNA polymerase forms the sugar-phosphate backbone - creating phosphodiester bonds
The pre mRNA is processed with introns removed and exons are spliced together
Then the mRNA will leave the nucleus

Question 29

What happens between tRNA and amino acids in translation?

Answer 29

The amino acids are activated by combining with the tRNA in the cytoplasm
They combine to a specific amino acid codon catalysed by an enzyme and uses ATP

Question 30

What happens in translation?

Answer 30

The ribosomes move along the mRNA and ‘reads’ the code
The tRNA molecules with their amino acids attached find their complementary codon in the mRNA
Each ribosome can take 2 tRNA molecules
The amino acids at the top bind forming a peptide bond using ATP in a condensation reaction
Continues until stop codon is reached

Question 31

What happens when two amino acids have formed a peptide bond in translation?

Answer 31

The first tRNA molecule is released separating from the amino acid and mRNA
It is sent back to the cytoplasm to find more amino acids

Question 32

When does translation end?

Answer 32

When it reaches a stop codon

Then the ribosome will detach from the mRNA

Question 33

What is the first amino acid in every translation?

Answer 33

Methionine - AUG

Question 34

How many ribosomes can you send along the mRNA? Why?

Answer 34

50 travelling behind each other

So you can translate many polypeptides at once

Question 35

How does protein synthesis occur differently in prokaryotic cells?

Answer 35

Translation occurs in the cytoplasm not nucleus
RNA polymerase copies the DNA in a circular strand not linear
Not introns to be removed therefore no pre mRNA

Question 36

Where does transcription occur in eukaryotic and prokaryotic cells?

Answer 36

In the cytoplasm