WARM-UP #7

DNA

(Deoxyribonucleic Acid)

Genetic material of cells…

• GENES – units of genetic material that

CODES FOR A SPECIFIC TRAIT

• Called NUCLEIC ACIDS

• DNA is made up of repeating molecules

called NUCLEOTIDES

DNA Nucleotide

O

O=P-O

O

Phosphate

Group

N Nitrogenous base

(A, G, C, or T)

CH2

O

C1 C4

C3 C2

5

Sugar

(deoxyribose)

A HISTORY OF DNA

• Discovery of the DNA double helix

A. Frederick Griffith – Discovers that a factor in diseased bacteria can transform harmless bacteria into deadly bacteria (1928)

B. Rosalind Franklin - X-ray photo of DNA.

(1952)

C. Watson and Crick - described the DNA molecule from Franklin’s X-ray.

(1953)

SEE p. 292-293

Watson & Crick proposed…

•DNA had specific pairing between the

nitrogen bases:

ADENINE – THYMINE

CYTOSINE - GUANINE

•DNA was made of 2 long stands of

nucleotides arranged in a specific

way called the “Complementary Rule”

DNA Double Helix

Nitrogenous

Base (A,T,G or C)

“Rungs of ladder”

“Legs of ladder”

Phosphate &

Sugar Backbone

DNA Double Helix

P

P

P

O

O

O

1

2 3

4

5

5

3

3

5

P

P

P O

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 C T A

BASE-PAIRINGS

C G

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

histones and coiled tightly to form

chromosomes

See p. 297

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. 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

1. Why is replication necessary?

2. When does replication occur?

3. Describe how replication works.

4. Use the complementary rule to

create 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 DNA

2. 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---T

G---C

C---G

T---A

A---T

G---C

A---T

G---C

C---G

A---T

G---C

T---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 Quiz 1. 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: UGGCAGUGC

tryptophan-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?