What you’ll learn

• How to relate the structure of DNA to its function

• How to explain the role of DNA in protein production.

• How to distinguish among different types of mutations.

What you will do in this section

• You will analyze the structure of DNA

• You will determine how the structure of DNA enables it to reproduce itself accurately

What is DNA?

• DNA produces proteins which carry messages to perform different functions

•  In all living cells, DNA molecules are the storehouses of information about heritable traits.

Structure of DNA  

DNA is a type of nucleic acidDNA stands for Deoxyribonucleic Acid

Nucleic Acids are a type of macromolecule.

There are two types:

DNA and RNA

The building blocks of Nucleic acids

are nucleotides

Nucleotides

• A nucleotide has 3 parts:–Simple sugar –Phosphate group–Nitrogen base

• The simple sugar and phosphate group do not change

–ex: In DNA – »simple sugar = deoxyribose

– In RNA simple sugar = ribose

The molecule of life• A nitrogen base is a molecule of carbon, hydrogen and nitrogen.

–There are four possible bases in DNA:

»adenine (A)

»guanine (G)

»Cytosine (C)

»Thymine (T)

The molecule of Heredity• Watson and Crick discovered the

structure of DNA –It is made of 2 chains or strands of

nucleotides linked by nitrogen bases.• Nitrogen bases link by hydrogen bonds

–They called it a double helix. (looks like a winding staircase)

The molecule of life

• The backbone of DNA (railing of the staircase) is deoxyribose sugar and phosphate linked together repeatedly.

The molecule of life• The “stairs” of the DNA are the nitrogen

bases– Amount of Adenine always = amount of

Thymine – Amount of Guanine always = amount of

Cytosine• So A = T and G = C (and vice versa)

– these are called complementary base pairs

The molecule of life• The bases pair randomly and causes

all of the differences between organisms of different species.–there is no limit to how many times

or how often a base appears in a code.

–this results in an infinite number of different combinations.

DNA Sequencing

• Each DNA sequence codes for something.– Example: the word dear and read use

the same letters, but mean something completely different from one another. The letters are just rearranged. It is the same with DNA.

– The closer the genetic relationship between organisms, the more similar their DNA sequence.

– Ex: chimp and human DNA is 99% identical in sequence.

Uses

• Scientists use similarities in DNA sequences to determine:–Evolutionary relationships

–Relation in organisms (offspring to parent)

–Criminal analysis

DNA Replication: Copying

• What happens before mitosis or meiosis can occur? DNA replication–DNA replication is the copying of DNA.–DNA has 2 strands, each strand is not

identical, but complementary.• To copy DNA, both strands must be copied.

How the process works.

– First, an enzyme breaks the hydrogen bonds between each nitrogen base pair.• It unzips the DNA.

– As the DNA unzips, the base pairs are free to link onto nucleotides floating in the surroundings.

How the process works Cont.– Another enzyme

attaches the nucleotides together to form new backbone and new base pair connections.

– The process continues until every part of the DNA has been unzipped and copied.

How it works continued again– Each new strand is

called the complementary strand.

– Each original strand is called the parent strand.

– When replication is complete, you have two DNA double helixes.

Before a cell divides, it makes an exact copy of each strand of DNA so that new cells will have a complete set of all genes. Sometimes during this process, your body makes a mistake. These mistakes are called mutations.