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DNA or Protein? Walter Sutton discovered chromosomes were made of DNA and Protein

However, scientists were NOT sure which one (protein or DNA) was the actual genetic material of the cell

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DNA! Frederick Griffith in 1928 showed the DNA was the cell’s genetic material

In 1944, Oswald Avery demonstrated that DNA is the material responsible for transformation.

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In 1952, Alfred Hershey and Martha Chase, proved that the DNA of a virus is injected into the bacterial cells. That then causes the bacterial cells to produce more viral DNA and proteins.

DNA’s role Revealed

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DNA DNA is often called

the blueprint of life.

In simple terms, DNA contains the instructions for making proteins within the cell that make up you.

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Why do we study DNA?

We study DNA for many reasons:

Important to all life on Earth

Medical benefits such as cures for diseases

Better food crops

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Gene – segment of DNA that is located in a chromosome and that codes for a specific hereditary trait.

Basic unit of heredity.

Each cell in the human body contains about 25,000 to 35,000 genes, which carry information that determines your traits.

Our genes are on our chromosomes.

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What is a Gene?

Chromosomes are made up of a chemical called DNA and proteins.

Chromosomes come in pairs, and there are hundreds, sometimes thousands, of genes in one chromosome.

There are 46 chromosomes in each human cell.

Draw and explain Figure 2 Chromosome structure on p.119 on the left side of your notebook.

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Chromosomes and DNA

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Deoxyribonucleic acid

Stores hereditary information

Found in all cells

Organic Comound made up of C, H,

O, N and P

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DNA

Watson & Crick in the 1950’s built the 1st model of

DNAWith the help of

Chargraff’s observations and

Wilkins and Franklin’s

photographs (x-ray diffraction)

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The Shape of DNA DNA is a very long polymer.

The basic shape is like two strands twisted around each other, like a winding staircase.

This is called a double helix.

Read the first paragraph on p. 194; then summarize what you read in your notes.

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The Double Helix Molecule

The DNA double helix has two strands twisted together.

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What are Nucleotides?

Each DNA strand is made of linked nucleotides.

Nucleotides are the subunits of DNA

Each nucleotide is made up of 3 parts:

1. phosphate group2. 5 carbon sugar

(deoxyribose)3. nitrogen base

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One Strand of DNA The backbone of the molecule is alternating phosphates and deoxyribose sugar

The teeth are nitrogenous bases. 15

phosphate

deoxyribose

bases

NucleotidesOne deoxyribose together

with its phosphate and base make a nucleotide.

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C C

C

OPhosphate

O

CC

O -P OO

O

O -P OO

O

O -P OO

O

Nitrogenous base

Deoxyribose

One Strand of DNA

One strand of DNA is a polymer of nucleotides.

One strand of DNA has many millions of nucleotides.

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nucleotide

Cytosine C Thymine T

Adenine A Guanine G

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Four nitrogenous bases

DNA has four different bases:

Pyrimidines are single ring bases.

Purines are double ring bases.

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Two Kinds of N Bases in DNA

C

C

C

C

N

N

O

N

CC

CC

N

N

N

N

N

C

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

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Thymine and Cytosine are pyrimidines

C

C

C

C

N

N

O

N

cytosine

C

C

C

C

N

N

O

O

thymine

C

Adenine and guanine each have two rings of carbon and nitrogen atoms.

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Adenine and Guanine are purines

C

C

C

C

N

N

N

Adenine N

N

C

C

C

C

C

N

N

O

N

Guanine N

N

C

Two 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?

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Hydrogen 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.

The bonds between cytosine and guanine are shown here with dotted lines

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C

C

C

C

N

N

O

N

C

C

C

C

N N

O

N

N

N C

Hydrogen Bonds, cont.

When making hydrogen bonds, cytosine always pairs up with guanine

Adenine always pairs up with thymine

Adenine is bonded to thymine here

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C

C

CC

N

N

N

N

N

C

C

C

C

C

N

N

O

O

C

Chargraff’s Rule:• Adenine and Thymine always join together

A T

• Cytosine and Guanine always join together

C G

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DNA by the Numbers Each cell has about

2m 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. 26

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

What is the complimentary strand according to the base

pairing rules:

ATCCATTGGACGA

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TAGGTAACCTGCT

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DNA ReplicationWhat: The process of making

a copy of DNA.

When: DNA replication occurs

during the synthesis (S) phase of the cell cycle, before a cell divides.

How Long: One chromosome can be

replicated in about 8 hours.

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Step 1 : DNA replication

Double helix unwinds

DNA helicases open the double helix by breaking the hydrogen bonds that link the complementary nitrogen bases.

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Replication Fork The areas where the

double helix separates are called replication forks because of their Y shape. Once the 2 strands are separated, additional proteins attach to each strand, holding them apart.

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Step 2: DNA replication

At the replication fork, enzymes known as DNA polymerases add nucleotides to the exposed nitrogen bases, according to the base-pairing rules.

As it moves along, two new double helixes are formed.

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Step 3: DNA replication

Process continues until all of the DNA has been copied and the polymerases are signaled to detach.

Results in two identical DNA strands.

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Checking for Errors Errors sometimes occur and

the wrong nucleotide is added to the new strand.

An important feature of DNA replication is that DNA polymerases have a “proofreading” role.

It can backtrack to remove the incorrect nucleotide.

Reduces errors in DNA replication to about one error per 1 billion nucleotides.

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RNA

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RNA Differs from DNA1. RNA has a sugar ribose

DNA has a sugar deoxyribose

2. RNA contains the nitrogen base uracil (U) so.. A pairs with U and C pairs with G

DNA has thymine (T)

3. RNA molecule is single-strandedDNA is double-stranded

Just like DNA…RNA is made up of the subunits called nucleotides.

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Structure of RNA

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Three Main Types of RNA Messenger RNA (mRNA) carries genetic information to the ribosomes

Ribosomal RNA (rRNA), along with protein, makes up the ribosomes

Transfer RNA (tRNA) transfers amino acids to the ribosomes where proteins are synthesized

More recently discovered RNA: Interference RNA (RNAi)

inhibit gene expression38

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