D.N.A. is a Nucleic Acid

D.N.A is capable of…… • carrying genetic information to next generation• directing the cell to follow its orders• being easily copied

DNA History Griffith 1928

Grew 2 distinct strains of bacteria (rough and smooth), injected mice and observed which died

Transformation: one strain permanently changed into another

More History… Avery 1944

Wanted to determine what was responsible for transformation

Used enzymes to determine that DNA was the transforming factor.

Hershey-Chase 1952Studied viruses (bacteriophages)

Determined that genetic information was not protein but DNA

History of the Discovery of D.N.A

1952 – Rosalind Franklin studies the DNA molecule using a technique called X-ray diffraction.

History of D.N.A. Cont’d. Watson and Crick

They used Rosalind Franklin’s pictures of DNA to figure out the structure of D.N.A.

established the structure as a double helix - like a ladder that is twisted. The two sides of the ladder are sugar phosphate backbone and are held together by hydrogen bonds.

Basic Structure of D.N.A.

The sides of D.N.A. alternate Sugar and Phosphate. (sides of the ladder)

The bases make up the middle (rungs of the ladder)

A – T C - G

DNA: Deoxyribonucleic acid

The building blocks of DNA are nucleotides, each composed of:a 5-carbon sugar called deoxyribosea phosphate group (PO4)a nitrogenous base (4 types)

○ Adenine (A), thymine (T), cytosine (C), guanine (G)

Phosphate group

Nucleotide!

Deoxyribose (sugar)

9

DNA Structure

The two strands of nucleotides are antiparallel

Basically, one side runs “right side up and one side runs upside down”.

The 4 Bases Bases come in two types:

1. Pyrimidines (cytosine and thymine) – Have one ring of carbon

2. Purines (guanine and adenine) – Have two rings of carbon

Purines pair with Pyrimidines:

Adenine with Thymine Guanine with Cytosine

DNA Chromosome Structure

Think back: When did we learn that DNA had to be Think back: When did we learn that DNA had to be replicated??replicated??

During the cell cycle in S phaseDuring the cell cycle in S phase

DNA Replication

Replication Steps:

1. DNA unzips

2. New nucleotides assemble

3. Two new strands of identical DNA are reproduced – each with one original stand.

Replication Enzymes 2 Main enzymes involved 1. Helicase – unzips the DNA

2. DNA polymeraseIt has two main functions.

○ 1. Adds new bases○ 2. “proofreads”

The Big Picture When we want

to make a protein we have to transfer the “code” from DNA on to a special molecule called RNA!

This is called Transcription.

So how do we get from the code from the bases to really make us a protein?

RNA RNA stands for Ribonucleic

Acid. It is a special molecule that

carries the code from DNA out to the ribosomes so that we can make the right protein.

It is our messenger!!

RNARNASimilaritiesSimilarities PhosphatePhosphate SugarSugar BaseBase

DifferencesDifferences Sugar is Sugar is riboseribose (DNA: (DNA:

deoxyribose)deoxyribose) SingleSingle stranded (DNA: stranded (DNA:

double helix)double helix) Has Has uraciluracil as a base, not as a base, not

thyminethymine It can travel outside of the It can travel outside of the

nucleus.nucleus.

Proteins What is a protein?

A protein is a large molecule made of smaller parts called amino acids. Every protein has a specific order of amino acids!○ 20 amino acids exist in nature

○ The instructions for the order of amino acids comes from DNA

Proteins are the building block for ALL living things!

What do proteins do?Proteins have a

variety of different functions that include:

○ Structure○ Transport○ Enzymes○ Storage○ Hormonal ○ Movement ○ Defense

What proteins do… Proteins have several functions…

Structure○ Keratin: protein found in hair, fur and feathers

Transport○ Hemoglobin: transports oxygen in vertebrates

Enzymes○ Digestive enzymes: break down food

Storage○ Casein: found in milk, gives protein to young mammals

Hormonal ○ Insulin: regulates blood sugar

Movement ○ Actin and Myosin: responsible for muscle movement

Defense○ Antibodies: fight of infection and disease (immune system)

Protein Production Where is DNA located in the cell?

Nucleus!

Where are proteins produced?

Ribosomes in the cytoplasm!

How do we get the instructions from the nucleus to the ribosomes?

RNA!

Transcription Transcription is the process of copying

the code of DNA into RNA so it can go to the ribosome and make protein.

Transcription takes places in the NUCLEUS

A-U

C-G

T-A

TranscriptionTranscription3 STEPS3 STEPS

1. 1. RNA polymeraseRNA polymerase (another enzyme) binds to the (another enzyme) binds to the promoterpromoter region region of DNAof DNA

2. RNA polymerase 2. RNA polymerase unzipsunzips the DNA and adds nucleotide bases the DNA and adds nucleotide bases

A-U, C-GA-U, C-G

3. RNA polymerase stops when it comes to a 3. RNA polymerase stops when it comes to a terminationtermination region of region of DNADNA

Practice/Review

So if one side of DNA has the following bases, what would the other side have?

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

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

Using the original strand above, what would the RNA strand look like?

U G A C C A U G C U A U

Translation

Translation – converting mRNA into a protein.

To do this we use transfer RNA

Now that we have our mRNA it is time to make a protein…..we do this at the ribosome.

Transfer RNA Transfer RNA (tRNA) looks

like a cross. It has three bases that attach at the bottom.

We call these anti-codons. They attach to three bases on

the mRNA which we call codons.

At the top of the tRNA is an amino acid (the building block of proteins)!!

Steps – 8 easy steps!!

1. The newly made mRNA travels to the ribosome.

2. The ribosome reads the mRNA code in groups of three, called “codons.” Starts at AUG

3. Codons match up with anticodons

4. Another tRNA attaches to the next codon. Its amino acid is attached to the previous one.

Translation

5. The first tRNA falls off

6. The ribosome moves along the mRNA, using tRNA to attach amino acids.

7. The process ends when a stop codon is reached (UGA, UAA, UAG).

8. The amino acid chain is released – it FOLDS into a 3-D structure called a protein.

Translation

Amino Acid Chart So how do we know what amino acid is at the top of each transfer RNA? We use this cool

chart. Start at the middle and work towards the outside. Remember amino acids go together to make proteins.

This chart is based on mRNA codons!!

Practice:1. UCCSerine2.AAGLysine3.UAAStop

Let’s Pull everything together!

Practice Given the following DNA strand, give the corresponding

mRNA strand that it would code for. DNA T A C A C C T C A A T T mRNAA U G U G G A G U U A A

Now, use your chart and figure out the amino acid chain, that this mRNA would code for.

Methionine – Tryptophan – Serine – STOP http://learn.genetics.utah.edu/content/begin/d

na/transcribe/

MutationsMutations Mutations are changes in the DNA sequence Mutations are changes in the DNA sequence that affect genetic informationthat affect genetic information

1. Point Mutation1. Point MutationSubstitution – base changedSubstitution – base changed

○ Original strand: TAC GOriginal strand: TAC GCCA TGGA TGG○ Mutated strand: TAC GMutated strand: TAC GTTA TGGA TGG

2. Frameshift Mutation2. Frameshift MutationInsertion –base addedInsertion –base added

○ Original strand: TAC GCA TGGOriginal strand: TAC GCA TGG○ Mutated strand: TAMutated strand: TATT CGC ATG G CGC ATG G

Deletion – base removedDeletion – base removed○ Original strand: TOriginal strand: TAAC GCA TGGC GCA TGG○ Mutated strand: TCG CAT GGMutated strand: TCG CAT GG

MutationsMutations

Types of chromosomal Mutations Types of chromosomal Mutations (changes in whole chromosomes):(changes in whole chromosomes):