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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 changes which take place in cells

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

The kind of organism which is produced (buttercup,giraffe, herring, human 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 nitrogenous base (A, T, C, G)

DNA molecule 3

Ribose is a sugar, like glucose, but with only fivecarbon atoms in its molecule (found in RNA)

Deoxyribose is almost the same but lacks one oxygen atom (found in DNA)

Both molecules may be represented by the symbol

Ribose & deoxyribose 4

Pentose (5-carbon) sugars. Always represented by pentagons

The most common organic bases are

Adenine (A)

Thymine (T)

Cytosine (C)

Guanine (G)

The bases 5

The deoxyribose, the phosphateand one of the bases

adenine

deoxyribose

PO4

Combine to form a nucleotide

This is a structure of a NUCLEOTIDE 6

(Phosphate + sugar + nitrogen base) = nucleotide

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

Parts of a Nucleotide

A, T, C, G

Phosphate + Pentose sugar + Nitrogen Base (deoxyribose)

(ribose)

In fact, the DNA usually 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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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

PO4

PO4

PO4

PO4

PO4

PO4

PO4

PO4

PO4

PO4

PO4

PO4

PO4

2-stranded DNA 9

Hydrogen bond found between Nitrogen bases

Covalent bonds found b/t sugars and phosphates

Nitrogen base

sugar

Phosphate

sugar-phosphatechain

bases

THE DOUBLE HELIX

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The paired strands are coiled into a spiral called

A DOUBLE HELIX

The term “Double Helix” was coined by two British Scientists named James Watson and Francis Crick in the 1950s...but should they have received the Nobel Prize??

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If you haven’t already done so. Do a quick search and read about Watson & Crick and Rosalind Franklin.

On my webpage, there are questions for you to answer in your notes

A DIY model ofpart of a DNA moleculecan be found at Wal-Mart

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1. Before a cell divides, the DNA strands unwind and separate

2. Each strand makes a new partner by addingthe appropriate nucleotides

3. The result is that there are now two double-stranded DNA molecules in the nucleus

4. So that when the cell divides, each nucleus contains identical DNA

5. This process is called replication

DNA replication16

PO4

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1. The strands separate

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During DNA replication, the weak hydrogen bonds between the bases break—and the DNA unzips

PO4

PO4

PO4

PO4

PO4

PO4

PO4

PO4

PO4

PO4

PO4

PO4

PO4

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PO4

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PO4

2-4. Each strand builds up its partner by adding the appropriate nucleotides

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Two new strands of DNA have been copied

RNA (ribonucleic acid)

Ribonucleic Acid

• Single stranded form of DNA

• Responsible for Protein synthesis (making proteins)

• Travels to the ribosomes (since the DNA cannot leave the nucleus), and aids in protein synthesis

There are three types:• Messenger RNA (mRNA)-brings message from DNA• Ribosomal RNA (rRNA)- makes structure of ribosome• Transfer RNA (tRNA)-transfers the amino acid to the

site of protein synthesis

DNA vs. RNA (please copy this table)

DNA RNA

Number of Strands 2 1

Nitrogen Bases A, T, C, G A, U, C, G

Sugar Deoxyribose Ribose

Base Pairing A=TC=G

A=UC=G

Job (function) Genetic material, instructions for cell

function

Protein synthesis, making proteins

Location Nucleus Travels through cytoplasm ribosomes

DNA to Proteins

Protein Synthesis

Instructions for making proteins

• DNA inside of the nucleus gives instructions for protein synthesis.

• The DNA cannot leave the nucleus, so the mRNA must travel to the ribosomes

• The RNA helps the ribosomes to make proteins.

The sequence of bases in DNA forms the Genetic Code

A group of three bases (a triplet or codon) controlsthe 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

RNA Base Pairing

• DNA & RNA share many similarities and differences.

• One of the main differences in the base pairing.

• There is no THYMINE in RNA…there is URACIL

• So A = U

• Example

• DNA Strand AAT CGC CAT

• RNA Strand UUA CGC GUA

Rules of Protein synthesis

• 1. You are given a DNA base strand

• 2. You must convert it to mRNA

• 3. Find the amino acid that codes for the mRNA (p. 292 in Blue textbook has an amino acid chart)

• FYI-chains of amino acids make PROTEINS.

Example:

DNA base strand: AAA CAT

mRNA strand: UUU GUA

AMINO ACID: Phenylalanine Valine

The Central Dogma (Protein Synthesis)

DNA RNA Proteins

DNA inside of the nucleus gives instructions for Protein synthesis

mRNA travesls through the cytoplasm to the ribosomes where proteins

The chains of amino acids make proteins

DNA codon: AAA

RNA codon:UUU

Amino Acid: Phenylalanine

For example

Cytosine

Adenine Codes for Valine

Cytosine (C)

Guanine (G)

Adenine (A)

Codes for Alanine

Thymine

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

The proteins build the cell structures

They also make enzymes (enzymes are proteins)

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

A sequence of triplets in the DNA molecule may code for a complete protein

Such a sequence forms a gene

There may be a thousand or more bases in one gene

Genes 24

Question 1

Which of the following are components of nucleotides?

(a) deoxyribose

(b) amino acids

(c) phosphate

(d) enzymes

(e) organic bases

Question 2

Which of the following represent a correct pairing of bases?

(a) adenine with thymine

(b) adenine with guanine

(c) thymine with adenine

(d) guanine with cytosine

(e) thymine with thymine

Question 3

DNA molecules are formed from

(a) organic bases

(b) amino acids

(c) deoxyribose

(d) nucleotides

Question 4

Which of the following are organic bases?

(a) Valine

(b) Guanine

(c) Thymine

(d) Serine

Question 5

Replication of DNA occurs

(a) During cell division

(b) before cell division

(c) at any time

Question 6

A nucleotide triplet codes for

(a) a protein

(b) an amino acid

(c) an enzyme

(d) an organic base

Answer

CORRECT

Answer

INCORRECT