DNA: Structure and Function

Chapter 12

Section 1

Deoxyribose Nucleic Acid The Architect of Life The Molecule of Heredity The Blueprint of LifeThe First three-dimensional xerox machine

Life Instruction Manual

DNA

Why Study DNA?

To truly understand genetics, biologists first had to discover the chemical structure of the geneThis would then help them understand how genes control the inherited characteristics of living thingsGene expression is what enables cells of the same organism to take on so many different sizes, shapes and functions (even though just about every cell in an individual contains the same DNA)

1.What organelle is known as the control center of the cell?

2.What structures are found in the nucleus?

3.What are short segments of chromosomes?

4. What are genes/chromosomes composed of?

5. How do genes/chromosomes control the activity of the cell?

Review

nucleus

chromosomes

genes

DNA

produce proteins thatregulate cell functions and become cell structures

ReviewReview

History

1869 - Friedrich Miescher – “discovered” DNA in nucleus1928 - Frederick Griffith – Identified DNA as source of genetic material using bacteria1930’s - Oswald Avery, Colin MacLeod and Maclyn McCarty - Confirmed that genes made of DNA1950 - Alfred Hershey and Martha Chase confirmed DNA is the biochemical of heredity using radioactive markers bacteriophages1952- Maurice Wilkins and Rosalind Franklin X-rayed DNA to show repeating nucleotide structure1953- James Watson and Francis Crick combined data to create a 3-D model of structure called the double helix

Oswald Avery Maclyn McCarty

Martha Chase Alfred HersheyRosalind Franklin

X-ray of double helix

James Watson Francis Crick Frederick Griffith

Watson-Crick Model

• Is a polymer of 1000’s of nucleotide monomers • Is a double strand of covalently bonded nucleotides in twisted ladder shape

•twisted ladder shape = double helix

DNA Structure

Double helix: 2 spirals wound around each other

DNA Shape

But joined in

the middle

• Is a polymer of 1000’s of nucleotide monomers • Is a double strand of covalently bonded nucleotides in twisted ladder shape twisted ladder shape = double helix• ‘Rungs’ of ladder = nitrogen bases• ‘Sides’ of ladder = sugar & phosphate groups (also called the DNA backbone)

DNA Structure

SugarPhosphateBackbone

•Nucleotide- Individual unit of DNA.•Made of three parts:

•Deoxyribose (5-carbon sugar) •Phosphate group•A nitrogen-containing base

Nucleotide

•Four nitrogen-containing bases•Adenine•Guanine•Cytosine•Thymine

Bases

sugar (deoxyribose)

adenine A

base with a double-ring

structure

guanine (G)

base with a double-ring

structure

cytosine (C)

base with a single-ring structure

thymine (T)

base with a single-ring structure

Adenine double ringed =

Guanine

Thymine single ringed =

Cytosine

Bases

purines

pyrimidines

Deoxyribose (like ribose) is a sugar with 5 carbon  atoms in a ringOxygen is one of the ring members

In Deoxyribose, one of the OH groups is missing and replaced with hydrogenThus deoxy = - 1 oxygen

Nucleotide

sugar

baseP

OHH

P - the Phosphate groupIs important because it links the sugar on one nucleotide with the phosphate of the next nucleotide to make a polynucleotideNucleotides are connected to each othervia a covalent bond

Nucleotide

sugar

baseP

• Bases are paired together in specific manner Because of chemical structure and shape

•Adenine only pairs with Thymine•Guanine only pairs with Cytosine

Exactly enough room for only one purine and one pyramide base between the two strands of DNA

‘Base Pairing Rule’

•Bases held together in ‘rungs’ by weak hydrogen bonds

•2 hydrogen bonds between A & T•3 hydrogen bonds between C & G

‘Base Pairing Rule’

DNA

• Scientists wondered how DNA worked. They knew genes do these critical things:• Carry information from one generation to another• Put information to work to determine an organism’s characteristics

• Can be easily copied• Store and transmit genetic information needed for all cell functions• In order to do these things it had to be a special molecule!

DNA Function

• Our knowledge of DNA put to use:• Inheritance/ Genetic Counseling• Cell function/protein synthesis• Embryonic development/gene regulation• Evolution/ phylogenetic relationships• Medicine/genetic diseases• Genetic engineering/ recombinant DNA

Understanding DNA

Structure of DNA Review

Hydrogen bonds

Nucleotide

Sugar-phosphate backbone

Key

Adenine (A)

Thymine (T)

Cytosine (C)

Guanine (G)

Structure of DNA Review

Adenine Guanine Cytosine Thymine

Phosphate group Deoxyribose

Purines Pyrimidines

Bases

To get an idea of the size of the human genome present in each of our cells, consider the followinganalogy: If the DNA sequence of the human genome were compiled in books, the equivalent of 200 volumes the size of a Manhattan telephonebook (at 1,000 pages each) would be needed tohold it all. It would take about 9.5 years to read out loud (without stopping) the 3 billion bases in one person's genome sequence, calculated on a reading rate of 10 bases per second, equaling 600 bases/minute, 36,000 bases/hour, 864,000 bases/day, 315,360,000 bases/year.

DNA’s Size

Human Genome Project

DNAHow Am I Packaged?

• Nitrogen bases

1. Are like letters in the code

2. Put them in different order make a different gene

A

G

TC

DNAPackage

• Genes

1. Are like words made up of letters

2. A group of nitrogen bases that makes sense

3. Tells the cell to do something

CAT

DOG

HAT

A

A

T

C

• DNA strand

1. Are like sentences made up of words

2. A long line of genes on each DNA strand

DNAPackage

The cat sat.

One dog ate.

The big hat.

DNAPackage

• Chromosomes

1. Are like books full of sentences

2. DNA strand twists around and around itself

DNAPackage

• Nucleus

1. Is like a bookcase

2. Inside the cell, where all the chromosomes are stored

• So what would a library full of rows and rows of bookcases represent?

many cells together

which is a tissue

DNAPackage