DNAThe Molecule of Heredity

Chapter 11.1

DNA - Deoxyribonucleic Acid

•Contains genetic information (genes)

•Strands of repeating molecules that

make up our chromatin and chromosomes

DNA is called the “Blueprint of Life”

Why? • DNA tells cells which proteins to make • The proteins then cause our individual

characteristics

The Structure of DNA- DNA is in a Double-helix shape- It is double-stranded and

wound up like a twisted ladder- 2 strands attached to each other

Discovery credited to James Watson and Francis Crick.

Watson and Crick with DNA Model, 1953.

DNA Structure continued

It is a very long molecule made up of repeating subunits called nucleotides

3 Parts of a Nucleotide

1) Phosphate group

2) Simple sugar-DNA has a Deoxyribose sugar

-RNA has a Ribose sugar

3) Nitrogenous base-A, T, C, or G

4 Nitrogenous Bases in DNA

1. Adenine

2. Thymine

3. Guanine

4. Cytosine

Pyrimidines Purines

Special BasePairing Rules

*Adenine pairs with Thymine:

A-T

T-A

*Cytosine pairs with Guanine:

C-G

G-C

The DNA Strand * Bases held

together by hydrogen bonds.

* Sugar and phosphate are considered backbone

What are the proper pairings for the base strands shown:

1. A T C G T T T A C G C G T

2. T G C T A T A C C G T A A

3. C T A G C G A T G T C G T

Answers

1. A T C G T T T A C G C G T

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

2. T G C T A T A C C G T A A

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

3. C T A G C G A T G T C G T

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

New Strand = Complementary strand

Old Strand = Template Strand

RNA - ribonucleic acid

- Molecules that “read” the DNA and make proteins using the information in DNA

-RNA are the worker molecules.

3 ways RNA is different from DNA

• 1. RNA is single stranded

• 2. RNA has the sugar ribose (not deoxyribose)

• 3. RNA has the nitrogen base uracil instead of thymine.

RNA nitrogenous bases • RNA bases

– Adenine– Uracil (in DNA this is thymine)– Cytosine– Guanine

– Rules: • Same pairing as DNA except a U goes where a T

was in DNA

– A pairs with U (A-U) and C pairs with G (C-G)

RNA base pairing examples

IF the DNA strand is

A T C G G C A T

Then the RNA complement strand is

U A G C C G U A

IF the DNA is

A T A C G T A C G

Then the RNA complement strand is

U A U G C A U G C

Practice Time!

Three types of RNA • mRNA = Messenger RNA

– Carries information from nucleus to cytoplasm (ribosomes in cytoplasm)

• rRNA = Ribosomal RNA– Make ribosomes which are where amino

acids are assembled into proteins

• tRNA = Transfer RNA– Carries amino acids to the ribosome to be

assembled into proteins

DNA Replication - 2 from 1

2. During what phase of the cell cycle does

replication occur?

1. Why do cells need toreplicate their DNA before dividing?

4 Steps to DNA Replication

Step 1: Enzyme (helicase) initiates (starts) replication by unzipping the DNA

Step 2: Another enzyme (DNA polymerase) attaches new nucleotides following base pairing rules

Step 3: Error Checking

As it moves down the strand, the enzyme DNA polymerase:

1. Checks for errors2. Then fixes them

This process is called

proofreading

Mistake causes a bulge

DNA poly. repairs with correct base

DNA poly. finds & piece is cut out

DNA poly. continues down strand

Step 4:Original DNA

Original DNA

New DNA

2 Identical copies-1 old strand (template) -1 new strand (complementary)

Enzymes twist the new strands (creating the double helix)

Steps of DNA Replication

1. Enzyme (helicase) unzips the DNA2. Enzyme (DNA polymerase) attaches

new nucleotides according to base pairing rules

3. DNA polymerase checks for errors and fixes them.

4. End up with two identical daughter DNA strands that enzymes retwist.

STOPPING POINT

DNA Sequencing

Each organisms has a unique sequence of DNA

The closer two individuals are related, the more alike their sequences are.

What are some ways that we use this knowledge?

The Central Dogma

DNA Structure and

Base Pairs

(Adenine) A = T (Thymine)

( Cystosine) C = G (Guanine)