B8 DNA, Genes, Protein Synthesis

Question 1

What are the characteristics of eukaryotic cells?

Answer 1

Very long
Linear
DNA associated with proteins called histones
80s Ribosome

Question 2

What are the characteristics of prokaryotic cells?

Answer 2

Short
Circular
Not associated with proteins
70s Ribosomes

Question 3

Why is the DNA Double helix wound around the histones?

Answer 3

So it takes up as a little space as possible so it can fit in the nucleus and the histones support the DNA

Question 4

What do DNA and histones form when they are coiled up very tightly?

Answer 4

Chromosomes

Question 5

What 2 organelles also contain their own DNA and what are their characteristics?

Answer 5

The mitochondria and chloroplasts contain DNA which is short, circular and not associated with proteins

Question 6

What is a Gene?

Answer 6

A Gene is a base sequence of DNA that codes for either the amino acid sequence of a polypeptide or a functional RNA ( rRNA or tRNA)

Question 7

Which position does a gene occupy?

Answer 7

A gene always occupies a fixed position locus on a particular DNA molecule

Question 8

Definition of a Genome

Answer 8

The full set of genes in a cell

Question 9

Definition of a proteome

Answer 9

The full range of proteins a cell is able to produce

Question 10

What are the 3 main factors of genetic code?

Answer 10

Universal
Degenerate
Non overlapping

Question 11

What does it mean by genetic code being universal?

Answer 11

Same code is used in all living organisms

Question 12

What does it mean by genetic code being degenerate?

Answer 12

This means that more than one triplet codes for the same amino acid, reducing the number of mutations which are mistakes in the base.

Question 13

What does it mean by genetic code being non overlapping?

Answer 13

This means that each triplet is only read once and triplets dont share any bases

Question 14

What are the 2 areas of non-coding DNA?

Answer 14

Introns within genes
Non coding multiple repeats of bases sequences between genes

Question 15

What are introns?

Answer 15

Section of genes that dont code for anything. Non coding sequences

Question 16

Where do introns need to be removed?

Answer 16

Introns need to be removed before translation in gene splicing

Question 17

What are non coding multiple repeats of base sequences?

Answer 17

They are just the same base sequence repeated many times

Question 18

What are coding sequences called?

Answer 18

Exons

Question 19

What do exons do?

Answer 19

They are coding regions and they are expressed in the phenotype to make proteins

Question 20

What does mRNA stand for?

Answer 20

mRNA stands for messenger rna

Question 21

What is the function of messenger RNA?

Answer 21

It transfers genetic information from DNA to ribosomes, where it acts as a template for protein synthesis

Question 22

What does tRNA stand for?

Answer 22

tRNA stands for transfer rna

Question 23

What is the function of Transfer RNA?

Answer 23

Transfers amino acids that are used to make proteins to ribosomes

Question 24

Describe the structure of messenger RNA?

Answer 24

Very long single polynucleotide strand
Consists of polymer of RNA nucleotides
Possesses information in form of codons

Question 25

What does the sequence of codon determine?

Answer 25

It determines the amino acid sequence of a specific polypeptide that will be made

Question 26

Describe the structure of Transfer RNA?

Answer 26

Shorter single polynucleotide strand
H bonds between specific base pairs causes the trna molecule folds into a cloverleaf shape
At one end, a specific sequence of three bases = anticodon. At the other end is an amino acid binding site

Question 27

What does ATP provide the amino acid and the TRNA molecule?

Answer 27

ATP provides the energy for the bond to form between the amino acid and the tRNA molecule

Question 28

What are the 2 steps that allow proteins to be synthesised and in what order?

Answer 28

1. Transcription
2. Translation

Question 29

Definition of Transcription

Answer 29

The production of mRNA from DNA

Question 30

Where does transcription take place in eukaryotic cells?

Answer 30

Transcription takes place in the nucleus

Question 31

Where does transcription take place in prokaryotic cells?

Answer 31

Takes place in the cytoplasm

Question 32

What are the first 2 steps of transcription?

Answer 32

1)DNA Helicase begins to unwind the DNA, exposing some the bases (which breaks H bonds)

2) Free RNA nucleotides associate with their exposed complementary bases on the antisense strand of the unwound DNA by H bonding. RNA polymerase adds each nucleotide to the mRNA polynucleotide chain by forming a phosphodiester bonds

Question 33

What are the last 2 steps of Transcription?

Answer 33

3) Once the RNA polymerase has passed by, H bonds between the uncoiled strands of DNA reform. The strands recoil into a double helix.

4) When RNA polymerase reaches a stop triplet code, it detaches from DNA and production of mRNA is complete

Question 34

What are the steps in gene splicing?

Answer 34

Introns are removed and exons are spliced together. This forms mature mRNA which is ready for translation by ribosomes. This occurs in the nucleus and the mature mRNA leaves through nuclear pores

Question 35

Definition of Translation

Answer 35

The production of polypeptides from the sequence of codons carried by mRNA

Question 36

What are the first 2 steps of Translation?

Answer 36

1) mRNA attaches to a ribosomes and tRNA collects amino acids from the cytoplasm and carries them to the ribosome. tRNA is a single stranded molecule with a binding site at one end thus it can only carry one type of amino acid and a triplet of bases
2) tRNA attaches itself to mRNA by complementary base pairing - 2 molecules attach to mRNA at a time

Question 37

What are the last 2 steps of Translation?

Answer 37

3) The aa attached to 2 tRNA molecules join by a peptide bond and then tRNA molecules detach themselves from the amino acids, leaving them behind
4) This process is repeated thus leading to the formation of a ppt chain until a stop codon is reached on mRNA and ends the process of protein synthesis

Question 38

What is a mutation?

Answer 38

They are changes in DNA which arise spontaneously during replication and any change in the base sequence or quantity of DNA is a mutation

Question 39

What are the 2 key types of mutation?

Answer 39

Substitution and Deletion

Question 40

How does substitution occur and what does it do?

Answer 40

This is when one nucleotide in the DNA sequence is replaced by another. The effect of the change in a amino acid is dependent on the role of the original aa in the overall shape and function of the protein.

Question 41

Why may substitution not always be harmful?

Answer 41

Due to the substituted nucleotide may code in that triplet for the same amino acid

Question 42

How does Deletion occur and what does it do?

Answer 42

A Deletion is when a nucleotide in the DNA sequence is lost. The result of this nucleotide being lost can cause a frame shift. A frame shift is when completely different amino acids are being coded for

Question 43

What are the 2 forms of mutations that occur in chromosomes?

Answer 43

Polyploidy and Non-disjunction

Question 44

How does Polyploidy occur and what does it do?

Answer 44

Changes can occur in the whole set of chromosomes so that an individual has 3 of more sets of chromosomes instead of 2

Question 45

How does Non-disjunction occur and what does it do?

Answer 45

Non - disjunction occurs when chromosomes fail to separate correctly in meiosis. As a result the gametes and zygotes formed will have one more or one less chromosome than they should.

Question 46

Name a genetic disease which is also a disability caused from non - disjunction

Answer 46

Down syndrome