Overview

DNA(Deoxyribonucleic Acid)

What is DNA?Deoxyribonucleic acid contains all the

genetic information for living organisms.

It is a very long molecule of repeating units called nucleotides, which contain nitrogenous bases of:

• adenine (A), • guanine (G), • cytosine (C), • and thymine (T)

Genetic material of cells…

• GENES – units of genetic material (DNA or RNA) that CODE FOR A SPECIFIC TRAIT

• DNA and RNA are NUCLEIC ACIDS

• DNA/RNA is made up of repeating molecules called NUCLEOTIDES

DNA Nucleotide

OO=P-O O

Phosphate Group

NNitrogenous base (A, G, C, or T)

CH2

O

C1C4

C3 C2

5

Sugar(deoxyribose)

DNA Double Helix

NitrogenousBase (A,T,G or C)

“Rungs of ladder”

“Legs of ladder”

Phosphate &Sugar Backbone

DNA Double Helix

P

P

P

O

O

O

1

23

4

5

5

3

3

5

P

P

PO

O

O

1

2 3

4

5

5

3

5

3

G C

T A

Nitrogenous Bases

• PURINES

1. Adenine (A)

2. Guanine (G)

• PYRIMIDINES

3. Thymine (T)

4. Cytosine (C) T or C

A or G

Chargaff’s Rule

• Adenine must pair with Thymine

• Guanine must pair with Cytosine

• Their amounts in a given DNA molecule will be about the same.

G CT A

BASE-PAIRINGS

CG

H-bonds

T A

Genetic Diversity…• Different

arrangements of NUCLEOTIDES in a nucleic acid (DNA) provides the key to DIVERSITY among living organisms.

The Code of Life…

• The “code” of the chromosome is the SPECIFIC ORDER that bases occur.

A T C G T A T G C G G…

DNA is wrapped tightly around small proteins called histones and coiled

tightly to form chromosomes

See p. 297

How do we pass this genetic code to our own cells our

offspring?• DNA must be

replicated before cells divide during mitosis or meiosis…

• What stage is DNA replicated in before cell division?

DNA Replication• DNA must be copied

• The DNA molecule produces 2 IDENTICAL new complementary strands following the rules of base pairing:

A-T, G-C

• Each strand of the original DNA serves as a template for the new strand See p. 298

DNA Replication• Semiconservative

Model:

1. Avery-McCarty-McLeod

2. Watson and Crick showed: the two strands of the parental molecule separate, and each functions as a template for synthesis of a new complementary strand.

.Parental DNA

DNA Template

New DNA

DNA Replication• Each strand gets a new

complimentary strand, synthesized from free-floating nucleotides.

• Each strand is synthesized in the 5’ to 3’ direction; one strand made in one direction and other strand in opposite direction (leading vs. lagging strands)

• Two identical strands of DNA are made

http://www.veoh.com/browse/videos/category/educational/watch/v1011706jGF8tJBF#

Enzymes Involved in DNA Replication

• Helicase: Unzips DNA by breaking the hydrogen bonds between the nitrogenous bases

• Primase: Attaches RNA primer to DNA strand

• DNA Polymerase III: Makes the new strand of DNA by adding DNA nucleotides

• DNA Polymerase I: Replaces RNA primer with DNA nucleotides

• Ligase: Seals the gap between Okazaki Fragments

1. Why is replication necessary?

2. When does replication occur?

3. Describe how replication works.

4. Use the complementary rule tocreate the complementary

strand:

A---?G---?C---?T---?A---?G---?A---?G---?C---?A---?G---?T---?

Replication Quiz

1. Why is replication necessary?So both new cells will have the correct DNA2. When does replication occur?During interphase (S phase).3. Describe how replication works.Enzymes unzip DNA and complementary

nucleotides join each original strand.4. Use the complementary rule to

create the complementary strand:

A---TG---CC---GT---AA---TG---CA---TG---CC---GA---TG---CT---A

Replication Quiz

(1961) Watson & Crick proposed…• …DNA controlled cell function by

serving as a template for PROTEIN structure.

• 3 Nucleotides = a triplet or CODON(which code for a specific AMINO ACID)

See p.303

• AMINO ACIDS are the building blocks of proteins.

DNA Transcription

• DNA can “unzip” itself and RNA nucleotides match up to the DNA strand.

• Both DNA & RNA are formed from NUCLEOTIDES and are called NUCLEIC acids.

See p.301

DNA Translation

• The cell uses information from “messenger” RNA to produce proteins

See p.304-305

We will discuss details

of this on a later date

Transcription/Translation Quiz1. Why is transcription necessary?

2. Describe transcription.

3. Why is translation necessary?

4. Describe translation.

5. What are the main differences between DNA and RNA.

6. Using the chart on page 303, identify the amino acids coded for by these codons:

UGGCAGUGC

1. Why is transcription necessary?Transcription makes messenger RNA (MRNA) to carry the code for proteins out of the nucleus to the ribosomes in the cytoplasm.

2. Describe transcription.

RNA polymerase binds to DNA, separates the strands, then uses one strand as a template to assemble MRNA.

3. Why is translation necessary?

Translation assures that the right amino acids are joined together by peptides to form the correct protein.

4. Describe translation.The cell uses information from mRNA to produce proteins.

5. What are the main differences between DNA and RNA.DNA has deoxyribose, RNA has ribose; DNA has 2 strands, RNA has one strand; DNA has thymine, RNA has uracil.

6. Using the chart on page 303, identify the amino acids coded for by these codons: UGGCAGUGCtryptophan-glutamine-cysteine

AMAZING DNA FACTS…

• DNA from a single human cell extends in a single thread for almost 2 meters long!!!

• It contains information equal to some 600,000 printed pages of 500 words each!!! (a library of about 1,000 books)

LET’S REVIEW DNA…LM p.44

1. List the conclusions Griffith & Avery, Hershey & Chase drew from their experiments.

2. Summarize the relationship between genes & DNA.

3. Describe the overall structure of the DNA molecule.

4. What are the 4 kinds of bases?