Mr. ColemanBiology

DNADNA• DNADNA is often called

the blueprint of life..• In simple terms,

DNA contains the instructions for making proteins within the cell.

Why do we study DNADNA?

We study DNA for many reasons, e.g.,

• its central importance to all life on Earth,

• medical benefits such as cures for diseases,

• better food crops.

Chromosomes and DNAChromosomes and DNA

• Our genes are on our chromosomes.

• Chromosomes are made up of a chemical called DNA.

The Shape of the MoleculeThe Shape of the Molecule

• DNA is a very long polymer.

• The basic shape is like a twisted ladder or zipper.

• This is called a double helix.

One Strand of DNAOne Strand of DNA

• Nucleotides consist of:– 1 sugar

– 1 phosphate

– 1 nitrogen base

• One strand of DNA has many millions of nucleotides.

nucleotide

One Strand of DNAOne Strand of DNA• The backbone of

the molecule is alternating phosphate and deoxyribose sugar

• The teeth are nitrogenous bases.

phosphate

deoxyribose

bases

Four nitrogenous basesFour nitrogenous bases

• Cytosine C• Thymine T

• Adenine A

• Guanine G

DNA has four different bases:

Important:Important:

• Adenine and Thymine always join together

A T

• Cytosine and Guanine always join together

C G

Two Kinds of Bases in DNA

• Pyrimidines are Pyrimidines are single ring bases.single ring bases.

• Purines are double Purines are double ring bases.ring bases.

C

C

C

C

N

N

OO

N

CC

CC

N

N

N

N

N

C

Thymine and Cytosine are Thymine and Cytosine are pyrimidinespyrimidines

• Thymine and cytosine each have one ring of Thymine and cytosine each have one ring of carbon and nitrogen atoms.carbon and nitrogen atoms.

C

C

C

C

N

N

OO

N

cytosinecytosine

C

C

C

C

N

N

OO

OO

thyminethymine

C

Adenine and Guanine are Adenine and Guanine are purinespurines

• AdenineAdenine and and guanineguanine each have two each have two rings of carbon and nitrogen atoms.rings of carbon and nitrogen atoms.

C

C

C

C

N

N

N

AdenineAdenine N

N

C

C

C

C

C

N

N

OO

N

GuanineGuanine N

N

C

Two Stranded DNATwo Stranded DNA• Remember, DNA

has two strands that fit together something like a zipper.

• The teeth are the nitrogenous bases but why do they stick together?

Hydrogen BondsHydrogen Bonds

• The bases attract each other because of hydrogen bonds.

• Hydrogen bonds are weak but there are millions and millions of them in a single molecule of DNA.

DNA by the numbersDNA by the numbers• Each cell has about 2 m

of DNA.• The average human has

75 trillion cells.• The average human has

enough DNA to go from the earth to the sun more than 400 times.

• DNA has a diameter of only 0.000000002 m.

The earth is 150 billion mor 93 million miles from the sun.

I. DNA ReplicationI. DNA ReplicationA. When a cell divides, it

needs to make a copy of its DNA so that both of the new cells have the right amount of DNA

I. DNA ReplicationI. DNA ReplicationB. The steps of DNA Replication

1. Separation of Strands- Enzyme unzips the DNA (breaks the hydrogen bonds)

2. Free Base Pairing- Free nucleotides pair up with the exposed nitrogen bases on the two half DNA strands

3. Base Bonding- Another enzymes zips the hydrogen bonds together

C. Two identical strands created!

Genes & ProteinsGenes & Proteins• Genes are where the ribosomes get the

information to build different proteins– A gene is one section of the DNA strand

• Different proteins make different traits– Eye color, height, hair color, etc

• Proteins are made of amino acids– The gene tells the ribosome what order to put the amino

acids

– If they get out of order the wrong protein is produced.

Protein Synthesis Protein Synthesis (Making Proteins)(Making Proteins)

• Step 1: Transcription- Making a one sided copy of the DNA message called mRNA– Enzymes read the DNA in order to produce mRNA

– RNA is made from ribose sugars and only has one side

– RNA is small enough to leave the nucleus (DNA is not because it has two sides) This is why we call it messenger RNA—that’s what the m stands for!

– In RNA uracil replaces thymine (U instead of T)

• See anmation

Protein Synthesis Protein Synthesis (Making Proteins)(Making Proteins)

• Step 2: Translation-using mRNA and tRNA to link amino acids together to make proteins– Takes place in the ribosome– Ribosomes read mRNA and match it with the

appropriate tRNA molecule • The tRNA carry the amino acids to the ribosome

• See anmation

I now give you the Protein Synthesis Rap…

MutationsMutations• Mutation- Any permanent change in the order of

nucleotides in the DNA

– Causes different proteins to be made

– Some mutations can be good, but many are harmful

– Things that cause mutations:

• UV Rays

• Chemicals

• Smoking, Drinking, poor eating, etc

• Some happen naturally

• Etc