DNADNA

The common thread The common thread of life.of life.

What are the functions of DNA?What are the functions of DNA?

There are two main functions of DNAThere are two main functions of DNA– It is the molecule of heredity.It is the molecule of heredity.– It contains the information needed to construct proteins.It contains the information needed to construct proteins.

What is heredity?What is heredity?

Heredity is the term used to explain the Heredity is the term used to explain the transfer of genetic information from one transfer of genetic information from one generation to the next.generation to the next.

You inherited half of your DNA (your genes) You inherited half of your DNA (your genes) from Mom, and the other half from Dad. from Mom, and the other half from Dad.

DNA is the molecule that allows this to DNA is the molecule that allows this to happen.happen.

Structure of DNAStructure of DNA

As you surely As you surely remember the basic remember the basic building blocks of building blocks of DNA are DNA are nucleotides.nucleotides.

Here we see the Here we see the phosphate group phosphate group and 5-Carbon and 5-Carbon Sugar.Sugar.

Nitrogen bases.Nitrogen bases.

The third part of a nucleotide is the nitrogen The third part of a nucleotide is the nitrogen base.base.

There are two types of nitrogen bases:There are two types of nitrogen bases:Purines: A and G which have a double ring Purines: A and G which have a double ring structure.structure.Pyrimidines: T and C which have a single ring.Pyrimidines: T and C which have a single ring.

Genes to Proteins.Genes to Proteins.

Your DNA is housed in the nucleus of every cell in Your DNA is housed in the nucleus of every cell in your body. your body.

Most of the time, the DNA is in long twisted Most of the time, the DNA is in long twisted strands called Chromatin. Very thin, and cannot strands called Chromatin. Very thin, and cannot be seen using a regular compound light be seen using a regular compound light microscope.microscope.

The Chromatin condenses to form Chromosomes The Chromatin condenses to form Chromosomes prior to cell division. These can be seen.prior to cell division. These can be seen.

Genes to proteins cont.Genes to proteins cont.

These strands of chromatin are made up of many These strands of chromatin are made up of many genes. A gene can be hundreds or thousands of genes. A gene can be hundreds or thousands of nucleotides long. (The entire human genome nucleotides long. (The entire human genome consists of 3 BILLION nucleotides).consists of 3 BILLION nucleotides).

Each gene is a series of nucleotides which Each gene is a series of nucleotides which contains the information to make a protein.contains the information to make a protein.

1 gene = 1 protein.1 gene = 1 protein.

The genetic codeThe genetic code

Genetists (Scientists who Genetists (Scientists who study genetics) were study genetics) were interested in determining how interested in determining how information in your genes was information in your genes was used to create proteins.used to create proteins.

They knew that there were 20 They knew that there were 20 different amino acids and that different amino acids and that there were 4 types of there were 4 types of nucleotide.nucleotide.

Cracking the code.Cracking the code.

Since there were twenty amino acids Since there were twenty amino acids and only 4 nucleotide types, they knew and only 4 nucleotide types, they knew that the genetic code had to consist of that the genetic code had to consist of more than one nucleotide.more than one nucleotide.

4411= 4 = 4 Ex. The nucleotide Ex. The nucleotide AdenineAdenine by itself by itself

does not code of the amino acid does not code of the amino acid Threonine.Threonine.

Cracking the code (cont.)Cracking the code (cont.)

By applying the same logic, they realized By applying the same logic, they realized that the genetic code could not consist of that the genetic code could not consist of two nucleotides either.two nucleotides either.

4422=16=16 Adenine Adenine and and CytosineCytosine together does not together does not

code for the amino acid code for the amino acid ThreonineThreonine..

Cracking the codeCracking the code Expanding on the theme, they realized that sequences of Expanding on the theme, they realized that sequences of

3 nucleotides would give more than enough combinations 3 nucleotides would give more than enough combinations to code for all 20 amino acids.to code for all 20 amino acids.

4433=64=64Adenine, CytosineAdenine, Cytosine and and GuanineGuanine DO code for the amino acid DO code for the amino acid

Threonine.Threonine.

They call these 3-nucleotide sequences They call these 3-nucleotide sequences CODONSCODONS..

We will be using the actual genetic code later in this unit.We will be using the actual genetic code later in this unit.

The Genetic CodeThe Genetic Code

Lets take a look.Lets take a look.DNA genetic codeDNA genetic code

DNA ReplicationDNA Replication Prior to cell division (mitosis or meiosis) the cell Prior to cell division (mitosis or meiosis) the cell

must make another copy of, or replicate it’s DNA.must make another copy of, or replicate it’s DNA. The DNA molecule basically unzips itself by The DNA molecule basically unzips itself by

breaking the hydrogen bonds holding the two breaking the hydrogen bonds holding the two strands of nucleotides together.strands of nucleotides together.

Each strand then forms a second strand by using Each strand then forms a second strand by using free nucleotides which are found in the nucleus.free nucleotides which are found in the nucleus.

DNA replication simpleDNA replication simple DNA replication complexDNA replication complex

DNA and RNADNA and RNA Both are nucleic acids, and are very similar Both are nucleic acids, and are very similar

to each other.to each other. There are some differences.There are some differences.

DNADNA RNA RNASugar:Sugar: DeoxyriboseDeoxyribose Ribose RiboseStrands:Strands: 22 1 1Nitrogen Base: Nitrogen Base: ThymineThymine Uracil UracilLocationLocation Nucleus Nucleus Nucleus &CytoplasmNucleus &Cytoplasm

RNA transcriptionRNA transcription While DNA contains an entire While DNA contains an entire

library’s worth of information, it is a library’s worth of information, it is a big, big molecule.big, big molecule.

It is so big, it cannot fit through the It is so big, it cannot fit through the pores of the nuclear membrane.pores of the nuclear membrane.

To get the information needed to To get the information needed to make proteins to the ribosomes, make proteins to the ribosomes, the DNA needs some help.the DNA needs some help.

Enter the messengerEnter the messenger

In order to get the information stored in a In order to get the information stored in a gene to the ribosome, messenger RNA gene to the ribosome, messenger RNA (mRNA) is transcripted.(mRNA) is transcripted.

First, the DNA will partially unzip itself to First, the DNA will partially unzip itself to expose one gene’s worth of code.expose one gene’s worth of code.

An enzyme called RNA polymerase then An enzyme called RNA polymerase then copies a strand of RNA based on the copies a strand of RNA based on the template strand of the DNA.template strand of the DNA.

mRNA transcriptionmRNA transcription

RNA transcription simpleRNA transcription simple RNA transcription complexRNA transcription complex