Topic Four Biology

Question 1

How is DNA stored in eukaryotic cells?

Answer 1

Eukaryotic cells contain linear DNA
Exist as chromosomes - thread like structures
Chromosomes found in nucleus
DNA molecule really long so wound around proteins called histones ( help support DNA)

Question 2

Mitochondria and Chloroplast DNA

Answer 2

Pretty similar to prokaryotic DNA
Circular
Shorter
No histone protiens

Question 3

How is DNA stored in Prokaryotic cells?

Answer 3

DNA molecules shorter and circular
DNA isn’t wrapped around histones
It condenses to fit into cell by suoercoiling

Question 4

Genes

Answer 4

• DNA contains genes
• A gene is a sequence of DNA bases that codes for either a polypeptide or functional RNA
• Sequence of amino acids in a polypeptide forms the primary structure of a protein

Question 5

What is an amino acid coded for ?

Answer 5

• a sequence of three bases called a triplet or codon
• to makes a polypeptide DNA is first copied into messenger rna

Question 6

What happens to genes that do not code for a polypeptide?

Answer 6

• code for functional rna instead
• eg tRNA and ribosomal RNA (rRNA)

Question 7

Genome

Answer 7

Complete set of genes in a cell

Question 8

Proteome

Answer 8

Full range of proteins that the cell is able to produce

Question 9

Introns

Answer 9

Part of a gene that does not code for polypeptides in eukaryotes
Prokaryotic dna does not contain intron

Question 10

Exons

Answer 10

All parts of a gene that does code for amino acids

Question 11

Allele

Answer 11

A gene can exist in more than one form - order of bases in each allele is slightly different so they code for different versions of the same polypeptide

Question 12

Homologous chromosomes

Answer 12

• pairs of matching chromosomes
• same size
• same genes
• could have different alleles

Question 13

What is protein synthesis ?

Answer 13

• production of proteins from the information contained within a cells DNA
• two main stages
  Transcription - DNA copied into a molecules called mRNA
  Translation - where the mRNA joins with a ribosome and the code it carries is used to synthesise a proteins

Question 14

RNA

Answer 14

• SINGLE polynucleotide
• contains uracil
• uracil pairs with adenine
• different types mRNA and tRNA

Question 15

Messenger RNA

Answer 15

mRNA - made during transcription
- carries genetic code from DNA to ribosomes
- single polynucleotide strand
- groups of three adjacent bases usually called codons

Question 16

Transfer RNA

Answer 16

• tRNA - involved in translation
• carries the amino acids that are used to make proteins to the ribosomes
• single polynucleotide strand that is folded into a clover shape
• hydrogen bonds between specific base pairs hold the molecule in this shape
• anticodon - specific sequence of three bases at one end

Question 17

Where does transcription take place?

Answer 17

Eukaryotes - nucleus
Prokaryotes - cytoplasm

Question 18

Stages of transcription

Answer 18

1) RNA polymerase attaches to the DNA
- In eukaryotes the hydrogen bonds between the two DNA strands in a gene a broken by DNA helicase case
- This separates the strands and the DNA molecule uncoils
- Some of the bases are exposed
- Template strand used to make an mRNA copy

2) complementary mRNA is formed
- RNA polymerase lines up free RNA nucleotides alongside the exposed basis on the template strand
- Free bases are attracted to the exposed bases
- Specific Complementary base powering cars
- Once the RNA nucleotides are paired up with a specific base on the DNA strand they’re joined together by RNA polymerase

3) RNA polymerase moves down DNA strand
- Assembles mRNA strand
- hydrogen bonds between the uncoiled strand of DNA reform once the RNA polymerase has passed by
- Strands coil back into a double helix

4) RNA polymerase reaches stop signal
- Stop making mRNA and detaches from the DNA
In eukaryotes mRNA moves out of the nucleus through a nuclear pore and attaches to a ribosome in the cytoplasm

Question 19

Editing mRNA

Answer 19

-In eukaryotes, intron and exons are both copied into our mRNA during transcription
-mRNA strands containing Introns and exons are called pre - mRNA
- Splicing removes Introns and the exons are joined together
- takes place in nucleus

Question 20

Translation - ( second stage of protein synthesis )

Answer 20

• In both eukaryotes and prokaryotes
• translations occurs in ribosomes in the cytoplasm
• mRNA attaches itself to the ribosome
• tRNA molecules carry amino acids to ribosomes
• ATP provides energy for the bond between the amino acid and tRNA to form

-tRNA molecule (carrying an amino acid) with an anticodon that’s complimentary to the first codon on the mRNA attaches itself to the mRNA by complimentary base pairing and so on
- amino acids attached to tRNA are joined by peptide bonds
-tRNA molecules move away from ribosome leaving amino acid behind
- empty tRNA molecules moves from ribosome
- this process continues producing a chain of amino acids called a polypeptide

Question 21

What is the genetic code ?

Answer 21

Sequence of base triplets in mRNA which code for specific amino acids
Base triplets do not share their bases - the code is non overlapping
Universal - same specific base triplets code for the same amino acids in all living things eg uau codes for tyrosine in all organisms
Degenerate - some amino acids are coded for by more than one triplet