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DNA stands for deoxyribose nucleic acid

This chemical substance is present in the nucleusof all cells in all living organisms

DNA controls all the chemical reactions which take place in cells

The kind of cell which is formed, (muscle, blood,nerve etc) is controlled by DNA

DNA 2

DNA is a very large molecule made up of a long chain of sub-units

The sub-units are called nucleotides

Each nucleotide is made up of

a sugar called deoxyribose

a phosphate group -PO4 and

an organic base

DNA molecule 3

Ribose is a sugar, like glucose, but with only fivecarbon atoms in its molecule

Deoxyribose is almost the same but lacks one oxygen atom

Both molecules may be represented by the symbol

Ribose & deoxyribose 4

The four organic bases are

Adenine (A)

Thymine (T)

Cytosine (C)

Guanine (G)

The bases 5

The deoxyribose, the phosphate and one of the bases

adenine

deoxyribose

PO4

Combine to form a nucleotide

Nucleotides 6

A molecule of DNA is formed by millions of nucleotides joined together in a long chain

PO4

PO4

PO4

PO4

sugar-phosphate backbone

+ bases

Joined nucleotides 7

DNA consists of a double strand of nucleotides

The sugar-phosphate chains are on the outsideand the strands are held together by chemical bonds between the bases

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PO4

PO4

PO4

PO4

PO4

PO4

PO4

PO4

PO4

PO4

PO4

PO4

PO4

PO4

PO4

PO4

2-stranded DNA 9

The bases always pair up in the same way

Adenine forms a bond with Thymine

and Cytosine bonds with Guanine

Bonding 1 10

Adenine Thymine

Cytosine Guanine

PO4

PO4

PO4

thymine

PO4

PO4

PO4

PO4

adenine

cytosine

PO4

guanine

Bonding 2 11

The paired strands are coiled into a spiral called

A DOUBLE HELIX

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sugar-phosphatechain

bases

THE DOUBLE HELIX

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How do we REPLICATE DNA?• DNA double helix unwinds• DNA now single-stranded• New DNA strand forms using

complementary base pairing (A-T, C-G)• Used to prepare DNA for cell division• Whole genome copied/replicated• This is called COMPLIMENTARY PAIRING

DNA unwinds

New DNA strand forms using complementary base pairing (A-T, C-G)

LETS PRACTICE Write the COMPLIMENTARY DNA strand

using the DNA base pairing rule

A C G A T A T C G A A T C G C A

The SEQUENCE of bases in DNA forms the Genetic Code

A group of three bases controls the production of a particular amino acid in the cytoplasm of the cell

The different amino acids and the order in which they are joined up determines the sort of protein being produced

Genetic code 1 19

Questions to be answered.. How do we get from the bases found in

DNA to amino acids? How do we get from a bunch of amino

acids to proteins?

How do we make proteins from DNA? DNA are the instruction booklet for how

proteins are made DNA must go through two processes :

TRANSCRIPTION AND TRANSLATION

Protein Structure Review Made up of amino acids Polypeptide- string of amino acids 20 amino acids are arranged in different

orders to make a variety of proteins Made in the RIBOSOMES (Protein

factories)

DNA

RNA

Protein

MAKING A PROTEIN STEP 1: TRANSCRIPTION

STEP 2: TRANSLATION

1st Process: TRANSCRIPTION Transcription: Making a strand of RNA

STEP ONE: DNA double helix must unwind into two

single strands. DNA double helix will unwind. This is done by the enzyme DNA HELICASE

Transcription Transcription is the first step of gene

expression, in which a particular segment of DNA is copied into RNA (mRNA) by the enzyme RNA polymerase.

Both RNA and DNA are nucleic acids, which use base pairs of nucleotides as a complementary language.

Step Two: TRANSCRIPTION

Transcription The enzyme RNA polymerase will come

in and begin creating a strand of RNA based on DNA sequence

A U C GOnly difference: A now pairs with U (Uracil) instead of T (Thymine)

DNA vs RNA DNA is double strandedRNA is single stranded

DNA contains ThymineRNA contains Uracil

DNA is used to make RNARNA is used to make a protein

DNA is used in transcriptionRNA is used in translation

LETS PRACTICE Create your RNA strand from this strand

of DNA

A C G A T A T C G A A T C G C A

2nd Process: TranslationTranslation: Building our protein from amino acids

Protein Structure Review Made up of amino acids Polypeptide- string of amino acids 20 amino acids are arranged in different

orders to make a variety of proteins

We will now create this chain of amino acids in TRANSLATION

Translation Every THREE nucleotides in RNA is

called a CODON RNA is then coded into amino acids Each codon codes for one amino acid

For example

Cytosine

Adenine Codes for Valine

Cytosine (C)

Guanine (G)

Adenine (A)

Codes for Alanine

Uracil

Coding 21

This is known as the triplet code

Each triplet codes for a specific amino acid

CGA - CAA - CCA - CCA - GCT - GGG - GAG - CCA -

Ala Val Gly Gly Arg Pro Leu Gly

Ala Val Gly Gly Arg Pro Leu Gly

The amino acids are joined together in the correct sequence to make part of a protein

Triplet code 22

Ser-Cyst-Val-Gly-Ser-Cyst Ala Val Val-Cyst-Ser-Ala-Ser-Cyst-Gly

Val- Cyst-Ala-Ala-Ser-Gly

This is a small, imaginary protein molecule showing how a sequence of 5 different amino acids could determine the shape and identity of the molecule

Each amino acid (Serine, Cysteine, Valine, Glycine and Alanine) is coded for by a particular triplet of bases

Genetic code 2 20

The proteins build the cell structures

They also make enzymes

The DNA controls which enzymes are made andthe enzymes determine what reactions take place

The structures and reactions in the cell determinewhat sort of a cell it is and what its function is

So DNA exerts its control through the enzymes

DNA and enzymes 23