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39 Cards in this Set

  • Front
  • Back

Structure of DNA

•double helix


•made of repeating units called nucleotides and link together to form sugar phosphate backbone


•nucleotide= deoxyribose sugar, phosphate and base


•contains hydrogen bonds between bases


•double stranded anti parallel structure





Base pairing

Adenine-thymine


Guanine-cytosine


Deoxyribose at what prime end

3' end

Phosphate at what prime end ?

5'

Type of DNA in prokaryotes

Circular chromosomal DNA and plasmids

Where are circular plasmids found

Prokaryotes and yeast

Where are circular chromosomes found

Mitochondria and chloroplasts of eukaryotes

How are chromosomes arranged in eukaryotes

Linear chromosomes in the nucleus tightly coiled and packaged with associated proteins

How are genotypes determined

By the sequence of bases

Genotype

Genetic informations of an organism

Process of DNA replication

1. Double helix unwind and weak hydrogen bonds break between base pairs


2.two strands separate, template strands become stabilises and expose their bases at y-shaped replication forks


3. DNA polymerase requires a primer


4.DNA polymerase can only add DNA nucleotides in one direction resulting in one strand being replicated continuously and the other strand replicated in fragments


4. Each fragment has to be primed so DNA polymerase can bind individual DNA nucleotides together


5. Ligase joins the fragments together, this form the lagging strand


6. Each strand twist or into a double helix


Primer

A short sequence of nucleotides formed at the 3'end of the parental DNA strand about to be replicated

DNA replication requires ?

•DNA to act as a template


• primers


• supply of 4 types of nucleotides


• enzymes- DNA Polymerase, ligase


• ATP

Why is DNA replication important ?

DNA is a molecule of inheritance


Ensures an exact copy of a species genetic information is passed from cell to cell during growth and repair and from generation to generation during reproduction

PCR

Technique for the amplification of DNA in vitro

Process of polymerase chain reaction

1. DNA is heated( denaturation 94-96) breaks Hbonds and strands separate


2. Cooling occurs (annealing 50- 65) for primers to bind to complementary target sequence


3. Heat tolerant DNA polymerase replicates the region of DNA by adding nucleotides at the 3'end of original DNA strand


4. Repeated cycles of heating and cooling to amplify this region of DNA


Practical applications of PCR

Tiny quantities of DNA can provide sufficient material for DNA finger printing


Paternity testing


Diagnosis of genetic disorders

Sources of DNA for PCR

Blood


Semen


Embryonic cells


Viruses


Preserved remains of extinct species

How is a genotype determined

Base sequence of the DNA in its genes

Phenotype is determined by...

The proteins produced as the result of gene expression, influenced by intra- and extra- cellular environmental factors

What is the switching on of genes controlled by ?

Transcription and translation. It can also be affected by external environmental factors - only a small no. Of genes in a cell are expressed

Gene expression is controlled by

Regulation of transcription and translation

Functions of proteins

ENZYMES- fold provide shape of active site, they speed up the rate of reactions


ANTIBODIES- y- shapes molecules made by white blood cells in response to foreign bodies known as antigens. ( fight off disease)


HORMONES- chemical messengers transported in the bloodstream to target tissue. ( e.g. insulin, ADH, HGH)


STRUCTURAL PROTEINS- found in cell membrane

2 main types of proteins

Fibrous and globular

Structure of mRNA

Singlestranded, replacement of thymine with uracil and deoxyribose with ribose compared to DNA.


Function of mRNA

mRNA carries a copy of the DNA code from the nucleous to the ribisome

What forms the ribisome

Protiens and rRNA

Transcription

1. Takes place in the nucleus


2.makes mRNA from the base order on DNA


3.the promoter is a region of DNA where transcription is started


4. RNA polymerase is the enzyme which controls transcription

Process of transcription:

1. DNA polymerase moves along the DNA, unwinding and unzipping the double helix and synthesising a primary transcript of DNA from RNA nucleotides by complimentary base pairing ( adenine-uracil, guanine-cytosine)


RNA polymerase can only add RNA nucleotides to the 3' end of a growing strand


2. The introns of the primary transcript of mRNA are non-coding regions and are removed in RNA splicing


3. The exons are coding regions and are joined together to form mature transcript.


4.The mature transcript moves out of the nucleus via a nuclear pore into the cytoplasm


5.DNA joins complimentary bases back together with weak hydrogen bonds and winds back I to a double helix

Translation

Takes place in a ribisome


Is the translation of mRNA into a polypeptide by tRNA at the ribisome


Process of translation

1. A ribisome binds to the 5' end of the mature transcript. This allows the start codon to be in the correct position


2. A molecule of tRNA carrying a specific amino acid becomes attached to the start codon on mRNA. It's anticodon will be complimentary to the codon


3. Weak Hbonds form temporally between the codon and anticodon


4. More tRNA molecules align with their codon


5.peptide bonds form between the amino acids


6.exit of tRNA molecules from the ribisome as polypeptide is formed


Start and stop codons exist

Purpose of tRNA

To carry a specific amino acid to the mRNA in the ribisome

Structure of tRNA

Has a triplet anticodon site and an attachment site for a specific amino acid

What happens to the tRNA after it has delivered the amino acid to the ribisome

They are reused, go and collect another amino acid from the cytoplasm

How can different proteins be expressed from one gene ?

Alternative RNA splicing and post transitional modification

Alternative RNA splicing

Different mRNA molecules are produced from the same primary transcript depending upon which segment are treated as introns and exons

Post transitional modification

Protein structure can be modified by cutting and combining polypeptide chains or by adding phosphate or carbohydrate groups to the protein

How are proteins held in a three dimensional shape?

Peptide bonds, hydrogen bonds, folded polypeptide chains and interactions between individual amino acids

State the importance of DNA replication to cells

To ensure each cell has identical DNA