DNA & RNAChapter 12

Objectives: Summarize the relationship between genes and DNA

Describe the overall structure of DNA

Summarize the events of DNA replication

Relate the DNA molecule to chromosome structure

DNA Think about this:

How do genes work?

What are they made of?

How do they determine the characteristics of an

organism?

Are genes single molecules?

Griffiths and

Transformation Accidental discovery

Griffith had isolated two slightly different

strains, or types, of pneumonia bacteria from

mice.

S – smooth: Disease causing bacteria

R – Rough: Harmless strain

Oswald Avery also worked with

Pneumococcus

Griffith’s Experiments

After heating the disease-causing bacteria, why did Griffith test whether material

from the bacterial culture would produce new colonies in a petri dish?

Transformation From the last test of his experiment, Griffith discovered that

somehow the heat-killed bacteria had passed their disease-causing bacteria.

Griffith called this process transformation because one strain of bacteria had apparently been changed permanently into another.

He hypothesized that when the live, harmless bacteria and the heat-killed bacteria were mixed, some factor was transferred from the heat-killed cells into the live cells.

That factor, he hypothesized, must contain information that could change harmless bacteria into disease-causing ones.

Since the ability to cause disease was inherited by the transformed bacteria's offspring, the transforming factor might be a gene.

Avery and DNA

What were they able to determine was the “transforming factor” and how?

Key Finding! Avery and other scientists discovered that the

nucleic acid DNA stores and transmits the

genetic information from one generation of an

organism to the next.

Oswald Avery

Colin Munro

MacLeod Maclyn McCarty

The Hershey-Chase

Experiment

What is a bacteriophage?

The Hershey-Chase

Experiment

What is a bacteriophage?

Radioactive Markers Grew phage viruses in two media radioactively

labeled with either

35S radioactive Sulfur isotope in their proteins

32P radioactive phosphorus isotope in their DNA

Infected bacteria with labeled phages

Why did they use Sulfur and Phosphorus as

markers?

Which radioactive marker was found inside the cell

Which molecule carries viral genetic information?

Conclusions

35S phage

Radioactive proteins stayed in supernatant

Viral protein DID NOT enter the bacteria

32P phage

Radioactive DNA stayed in pellet

Viral DNA DID enter bacteria

The point?

Confirmed DNA is the “transforming factor”

Hershey and Chase concluded that the genetic material of the bacteriophage was DNA, not protein.

Hershey & Chase

The Components &

Structure of DNA How does DNA, or any molecule for that matter,

could do the three critical things that genes were

known to do:

First, genes had to carry information from one

generation to the next;

second, they had to put that information to work by

determining the heritable characteristics of

organisms; and

third, genes had to be easily copied, because all of a

cell's genetic information is replicated every time a

cell divides.

DNA is composed of

nucleotides

The 4 nitrogenous

bases of DNA

Structure

The backbone of a

DNA chain is formed

by sugar and

phosphate groups of

each nucleotide.

Chargaff’s Rules discovered that the

percentages of guanine

[G] and cytosine [C] bases

are almost equal in any

sample of DNA.

the percentages of

adenine [A] and thymine

[T] bases are also almost

equal in any sample of

DNA.

Samples from all

organisms obey this rule

X-Ray Evidence

The Double Helix

Using clues from

Franklin's pattern,

within weeks

Watson and Crick

had built a

structural model

that explained the

puzzle of how

DNA could carry

information, and

how it could be

copied.

Watson and

Crick's model of

DNA was a

double helix, in

which two

strands were

wound around

each other.

Key Point DNA is a double helix in which two strands are

wound around each other.

Each strand is made up of a chain of nucleotides.

The two strands are held together by hydrogen

bonds between adenine and thymine and between

guanine and cytosine.

Quick Quiz The double helix structure of DNA was first described by

___________________.

The first major experiment that led to the discovery of DNA as the genetic material was conducted by __________. He used heat-killed bacteria in mice.

The scientist who identified the transforming agent in Griffith’s famous experiment as DNA was _________.

These scientists preformed an experiment to demonstrate that DNA is the genetic material in viruses. ______________________

This scientist’s X-ray diffraction data helped Watson and Crick solve the structure of DNA. _____________________

Chromosomes & DNA

ReplicationW

he

re is D

NA

fo

und in

th

e c

ell?

H

ow

is it o

rganiz

ed?

DNA & Chromosomes

Prokaryotic cells

lack nuclei and

many of the

organelles found in

eukaryotes.

Their DNA

molecules are

located in the

cytoplasm.Most prokaryotes have a single circular DNA

molecule that contains nearly all of the cell's genetic

information.

Eukaryotic DNAEukaryotic DNA is generally located in the cell nucleus in the form of a number of

chromosomes.

The number of

chromosomes

varies widely from

one species to the

next.

DNA LengthThe chromosome

of the prokaryote E.

coli, which can live

in the human colon

(large intestine),

contains 4,639,221

base pairs.

Chromosome Structure

Eukaryotic chromosomes

contain both DNA and

protein, tightly packed

together to form a

substance called

chromatin.

Chromatin consists of

DNA that is tightly coiled

around proteins called

histones

DNA Replication

During DNA replication, the DNA molecule separates into two strands, then

produces two new complementary strands following the rules of base pairing.

Each strand of the double helix of DNA serves as a template, or model, for the

new strand.

Complete the Strand Complete the Strand with the complimentary bases

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

DNA Proofreading

DNA polymerase proof reads the DNA strands as it adds

new nucleotides.

The DNA polymerase can only add a new nucleotide if

the previous nucleotide is correctly paired to its

complementary base.

If an error is found, the DNA polymerase goes back and

removes the incorrect nucleotide, adding a correct one

so that it may then proceed along the strand.

The DNA polymerase's proof reading ability limits errors

in DNA replication to about one in 1 billion nucleotides.

Recap, Please! Step 1: Helicase separates DNA strands

Step 2: SSBs Coat Single stranded DNA and RNA

Primase synthesizes RNA primers

Step 3: Polymerase Extends the DNA strand

Sliding clamps increase processivity

Step 4: RNase H removes the RNA primer, Polymerase

fills the gap & Ligase connects short DNA strands

Dissecting the Steps in DNA Replication

Strands are separated

Helicase unwinds the DNA double helix

The point where the DNA is separated into single strands and

new DNA will be synthesized is known as the Replication

Fork

Single Strand Binding Proteins (SSBs) quickly coat the

newly exposed single strand. Why?

They bind loosely to the DNA and are displaced when the

polymerase enzymes begin synthesizing the new DNA

strands.

Now that they are separated, the new DNA strands can

act as templates for the production of two new

complimentary DNA strands

Snapshot of DNA

Replication

The Players Helicase – made of 6 proteins arranged in a ring shape unwinds the

DNA double helix into two individual strands.

Single Strand Binding proteins (SSBs) – tetramers that coat the single stranded DNA preventing the DNA from reannealing to form double stranded DNA.

Primase – an RNA polymerase that synthesizes the short RNA primers needed to start the replication process.

DNA polymerase – Bean shaped enzyme that strings nucleotides together to form a DNA strand.

The Sliding Clamp – an accessory protein that helps hold the DNA polymerase on to the DNA strand during replication

RNase H – removes the RNA primers that previously began the synthesis.

DNA Ligase – links short stretches of DNA together to form one long continuous strand of DNA.

Some questions for you… Why is DNA replication essential to life?

How often/fast does replication occur?

What nucleotides are complimentary Pairs?

What pairs with Guanine?

What pairs with Cytosine?

What pairs with Adenine?

What pairs with Thymine?

What pairs with Uracil?

Quick Quiz Match the enzyme with

the function:

A. Helicases

B. Ligase

C. DNA Polymerase

D. RNA Polymerase

E. Primase

1. Joins Okazaki fragments together

2. unwinds and unzips the parent DNA molecule

3. add short segments of RNA primers to each DNA strand

4. Adds the appropriate nucleotides to the new DNA strands

Objectives How is the code of DNA translated into messenger

RNA?

How is messenger RNA transcribed into a protein?

Describe how to make a protein (beginning with a a

gene).

Bodies Cells DNA

Bodies are made up of cells

All cells run on a set of instructions

spelled out in DNA

DNA Cells Bodies

How does DNA code for cells &

bodies?

How are cells and bodies made from the

instructions in DNA?

DNA Proteins

Cells Bodies DNA has the information to build proteins

genes

How do proteins do all

the work Proteins

Proteins run living organisms

Enzymes

Control all chemical reactions in living organisms

Structure

All living organisms are built out of proteins

Cell Organization DNA

DNA is in the ____________

Genes = instructions for making proteins

Want to keep it there = protected

Locked in the “vault”

Types of RNA There are three main types of RNA: messenger

RNA, ribosomal RNA, and transfer RNA.

How does RNA polymerase

“know” where to start and stop

making an RNA copy of DNA?

RNA Editing

UCGCACGGU

For example, consider the following RNA sequence:

UGC-CAC-GGU

This sequence would be read three bases at a time

as:

The codons represent the different amino acids:

GENETIC CODE

What could

proteins possibly

have to do with

the color of a

flower, the shape

of a leaf, a

human blood

type, or the sex

of a newborn

baby.

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