AP BiologyAP Biology 2006-2007

Nucleic Acids

AP Biologyproteins

DNA

Nucleic Acids Function:

genetic material stores information

genesblueprint for building

proteins DNA RNA proteins

transfers informationblueprint for new cellsblueprint for next generation

AP Biology

AA

A

A

TC

G

CG

TG

CT

AP Biology

Nucleic Acids Examples:

RNA (ribonucleic acid) single helix

DNA (deoxyribonucleic acid) double helix

Structure: monomers = nucleotides

RNADNA

AP Biology

The P groups make the links that unite the sugars (hence a “sugar-phosphate backbone”

Nucleotides 3 parts

pentose sugar (5C) ribose in RNA deoxyribose in DNA

nitrogen base (C-N ring) phosphate (PO4) group

Nitrogen baseI’m the A,T,C,G or Upart!

NUCLEOTIDE STRUCTURE

PHOSPATE GROUP

SUGARRibose or

Deoxyribose

NUCLEOTIDE

BASEPURINES PYRIMIDINE

SAdenine (A)Guanine(G)

Cytocine (C)Thymine (T)Uracil (U)

AP Biology

The base is attached to the carbon atom 1 and the phosphate group to carbon atom 5 of the pentose sugar

Pentose Sugars•There are two related pentose sugars:- RNA contains ribose- DNA contains deoxyribose

RIBOSE DEOXYRIBOSE

CH2OH

H

OH

C

C

OH OH

C

O

H HH

C

CH2OH

H

OH

C

C

OH H

C

O

H HH

C

Spot the difference

© 2007 Paul Billiet ODWS

Two types of Nucleotides (depending on the sugar they contain)

1- Ribonucleic acids (RNA)The pentose sugar is Ribose (has a hydroxyl group in the 3rd carbon-OH)

2- Deoxyribonucleic acids (DNA)The pentose sugar is Deoxyribose (has just an hydrogen in the same place-H)

Deoxy = “minus oxygen”

DNA NucleotidesComposition (3 parts):

1- Deoxyribose sugar (no O in 3rd carbon)

2- Phosphate group3- One of 4 types of bases (all

containing nitrogen): - Adenine- Thymine (Only in DNA)- Cytosine- Guanine

RNA NucleotidesComposition ( 3 parts):

1- Ribose sugar (with O in 3rd carbon)2- Phosphate group3- One of 4 types of bases (all

containing nitrogen): - Adenine- Uracyl (only in RNA)- Cytosine- Guanine

AP Biology

Nitrogenous bases Purine = AGPure silver!

2 different nitrogenous bases purines

double ring N base adenine (A) guanine (G)

pyrimidines single ring N base cytosine (C) thymine (T) uracil (U)

Purines

Pyrimidines

THE SUGAR-PHOSPHATE BACKBONE

• The nucleotides are all orientated in the same direction

• The phosphate group joins the 3rd Carbon of one sugar to the 5th Carbon of the next in line.

P

P

P

P

P

P

© 2007 Paul Billiet ODWS

• The nucleotides in nucleic acids are joined by phosphodiester bonds

• The 3’-OH group of the sugar in one nucleotide forms an ester bond to the phosphate group on the 5’-carbon of the sugar of the next nucleotide

Reading Primary Structure• A nucleic acid polymer has

a free 5’-phosphate group at one end and a free 3’-OH group at the other end

• The sequence is read from the free 5’-end using the letters of the bases

• This example reads 5’—A—C—G—T—3’

Example of RNA Primary Structure• In RNA, A, C, G, and U are linked by 3’-5’ ester

bonds between ribose and phosphate

Example of DNA Primary Structure• In DNA, A, C, G, and T are linked by 3’-5’ ester

bonds between deoxyribose and phosphate

AP Biology

Nucleic polymer Backbone

sugar to PO4 bond phosphodiester bond

new base added to sugar of previous base

polymer grows in one direction

N bases hang off the sugar-phosphate backbone

The distribution of nucleic acids in the eukaryotic cell • DNA is found in the nucleus with

small amounts in mitochondria and chloroplasts

• RNA is found throughout the cell

Francis Crick and Jim Watson (1953)

The Experiment

5' 3'

“Watson”

“Crick”

5' 3'Watson-Crick DNA Model (1953)

•Antiparallel double helix

•DNA bases in the middle

•Sugar Phosphate backbone running along the outside

Watson-Crick Model• DNA consists of two nucleotide strands• Strands run in opposite directions• The pairing of the bases from the two strands is

very specific• The complimentary base pairs are A-T and

G-C-two hydrogen bonds form between A and T-three hydrogen bonds form between G and C

Watson-Crick Model

Each pair consists of a purine and a pyrimidine, so they are the same width, keeping the two strands at equal distances from each other Molecule is a double helix

AP Biology

2 strands of DNA helix are complementary

DNA IS MADE OF TWO STRANDS OF POLYNUCLEOTIDE P

P

P

P

P

P

C

G

G

T

A

A

P

P

P

P

P

P

G

C

C

A

T

T

Hydrogen bonds

DNA IS MADE OF TWO STRANDS OF POLYNUCLEOTIDE

• The sister strands of the DNA molecule run in opposite directions (antiparallel)

• They are joined by the bases• Each base is paired with a specific partner:A is always paired with T G is always paired with CPurine with Pyrimidine• This the sister strands are complementary

but not identical• The bases are joined by hydrogen bonds,

individually weak but collectively strong

Watson-Crick DNA Model (1953)

•Antiparallel double helix

•DNA bases in the middle

•Sugar Phosphate backbone running along the outside

•Bases are paired with each other

DNA Double HelixDNA 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

DNA bases can only pair one way

A T

G C

This is called complementarity

Complementarity

Complementarity allows the hereditary information to be copied

digitally.

Question: Why is digital copying an advantage?

DNA can be very accurately copied

There have been hundreds of billions of cell divisions since you were a single

fertilized egg.

Chargaff’s RuleChargaff’s Rule• AdenineAdenine must pair with ThymineThymine

• GuanineGuanine must pair with CytosineCytosine

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

G CT A

Composition of DNA• Chargaff showed:

– Amount of adenine relative to guanine differs among species

– Amount of adenine always equals amount of thymine and amount of guanine always equals amount of cytosine

A=T and G=C

Erwin Chargaff’s Data (1950-51)

Maurice Wilkins & Rosalind Franklin (1952): X-ray crystallography

Maurice Wilkins & Rosalind Franklin

The Experiment

X-rays

DNA crystal

Photographic film

X-ray diffraction from DNA crystal

Showed that DNA is a double helix

Showed that the bases are on the inside

Watson, Crick and Wilkins

Nobel Prize 1962

The Nobel PrizeThe Nobel PrizeCrick, Watson and Wilkins won the Nobel Prize for medicine in 1962. Maurice Wilkins was at King's College, London and was an expert in X-ray photography. His colleague, Rosalind Franklin, did brilliant work developing the technique to photograph a single strand of DNA. She received little recognition for this at the time and died tragically of cancer in 1958, so could not be recognized in the Nobel Award.

Where was Rosalind Franklin?

Rosalind Franklin (1920 - 1958)

Ribonucleic Acid (RNA)• RNA is much more abundant than DNA• There are several important differences between RNA

and DNA:- the pentose sugar in RNA is ribose, in DNA it’s deoxyribose- in RNA, uracil replaces the base thymine (U pairs with A)- RNA is single stranded while DNA is double stranded- RNA molecules are much smaller than DNA molecules

• There are three main types of RNA:- ribosomal (rRNA), messenger (mRNA) and transfer (tRNA)

Types of RNA

Ribosomal RNA• Ribosomes are the sites of protein synthesis

- they consist of ribosomal DNA (65%) and proteins (35%)- they have two subunits, a large one and a small one

• Messenger RNA carries the genetic code transcripted from DNA in the nucleus to the ribosomes in the cytoplasm- they are strands of RNA that are complementary to the DNA of the gene for the protein to be synthesized

Messenger RNA

Transfer RNA• Transfer RNA translates the genetic code from the

messenger RNA and brings specific amino acids to the ribosome for protein synthesis

• Each amino acid is recognized by one or more specific tRNA

• tRNA has a tertiary structure that is L-shaped- one end attaches to the amino acid and the other binds to the mRNA by a 3-base complimentary sequence

DNA vs RNA

Nucleosides and Nucleotides• A nucleoside consists of a nitrogen base linked by a

glycosidic bond to C1’ of a ribose or deoxyribose• Nucleosides are named by changing the the

nitrogen base ending to -osine for purines and –idine for pyrimidines

• A nucleotide is a nucleoside that forms a phosphate ester with the C5’ OH group of ribose or deoxyribose

• Nucleotides are named using the name of the nucleoside followed by 5’-monophosphate

Names of Nucleosides and Nucleotides

AMP, ADP and ATP• Additional phosphate groups can be added to the

nucleoside 5’-monophosphates to form diphosphates and triphosphates

• ATP is the major energy source for cellular activity

How DNA Works1- DNA stores genetic information in

segments called genes2- The DNA code is in Triplet Codons

(short sequences of 3 nucleotides each)

3- Certain codons are translated by the cell into certain Amino

acids.4. Thus, the sequence of nucleotides

in DNA indicate a sequence of Amino acids in a protein.

A HISTORY OF DNAA HISTORY OF DNA

• Discovery of the DNA double helixDNA 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…Watson & Crick proposed…•DNA had specific pairing between the DNA had specific pairing between the

nitrogen bases:nitrogen bases:

ADENINEADENINE – – THYMINETHYMINE

CYTOSINECYTOSINE - - GUANINEGUANINE

•DNA was made of DNA was made of 22 long stands of long stands of nucleotides arranged in a specific way nucleotides arranged in a specific way

called the called the “Complementary Rule”“Complementary Rule”

DNA Double HelixDNA Double Helix

NitrogenousNitrogenousBase (A,T,G or C)Base (A,T,G or C)

““Rungs of ladder”Rungs of ladder”

““Legs of ladder”Legs of ladder”

Phosphate &Phosphate &Sugar BackboneSugar Backbone

Nitrogenous BasesNitrogenous Bases• PURINESPURINES

1. Adenine (A)Adenine (A)

2. Guanine (G)Guanine (G)

• PYRIMIDINESPYRIMIDINES3. Thymine (T)Thymine (T)

4. Cytosine (C)Cytosine (C) T or C

A or G

Chargaff’s RuleChargaff’s Rule• AdenineAdenine must pair with ThymineThymine

• GuanineGuanine must pair with CytosineCytosine

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

G CT A

BASE-PAIRINGSBASE-PAIRINGS

CG

H-bonds

T A