1 DNA stands for deoxyribose nucleic acid This

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DNA stands for deoxyribose nucleic acid This chemical substance is present in the nucleus of 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 2

DNA molecule 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 -PO 4 and an organic base 3

Ribose & deoxyribose Ribose is a sugar, like glucose, but with only five carbon atoms in its molecule Deoxyribose is almost the same but lacks one oxygen atom Both molecules may be represented by the symbol 4

5 The bases The four organic bases are Adenine (A) Thymine (T) Cytosine (C) Guanine (G)

6 Nucleotides The deoxyribose, the phosphate and one of the bases Combine to form a nucleotide PO 4 adenine deoxyribose

Joined nucleotides 7 PO 4 A molecule of DNA is formed by millions of nucleotides joined together in a long chain PO 4 sugar-phosphate backbone + bases

8 DNA consists of a double strand of nucleotides The sugar-phosphate chains are on the outside and the strands are held together by chemical bonds between the bases

2 -stranded DNA PO 4 PO 4 PO 4 PO 4 9

Bonding 1 10 The bases always pair up in the same way Adenine forms a bond with Thymine Adenine Thymine and Cytosine bonds with Guanine Cytosine Guanine

11 Bonding 2 PO 4 adenine thymine PO 4 cytosine guanine PO 4

13 The paired strands are coiled into a spiral called A DOUBLE HELIX

14 THE DOUBLE HELIX bases sugar-phosphate chain

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

Genetic code 1 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 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

1 st 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 is the first step of gene expression, in which a particular segment of DNA is copied into RNA (m. RNA) 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 G Only difference: A now pairs with U (Uracil) instead of T (Thymine)

DNA vs RNA DNA is double stranded RNA is single stranded DNA contains Thymine RNA contains Uracil DNA is used to make RNA is used to make a protein DNA is used in transcription RNA is used in translation

LETS PRACTICE Create your RNA strand from this strand of DNA A C G AT A T C G A A T C G C A

2 nd Process: Translation: 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

Coding 21 For example Cytosine Adenine Codes for Valine Codes for Alanine Uracil Cytosine (C) Guanine (G) Adenine (A)

Triplet code 22 This is known as the triplet code Each triplet codes for a specific amino acid CGA - CAA - CCA - GCT - GGG - GAG - CCA Ala Val Gly Arg Pro Leu Gly The amino acids are joined together in the correct sequence to make part of a protein Ala Val Gly Arg Pro Leu Gly

Genetic code 2 20 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 Ser-Cyst-Val-Gly-Ser-Cyst Ala Val-Cyst-Ser-Ala-Ser-Cyst-Gly Val- Cyst-Ala-Ser-Gly Each amino acid (Serine, Cysteine, Valine, Glycine and Alanine) is coded for by a particular triplet of bases

DNA and enzymes The proteins build the cell structures They also make enzymes The DNA controls which enzymes are made and the enzymes determine what reactions take place The structures and reactions in the cell determine what sort of a cell it is and what its function is So DNA exerts its control through the enzymes 23