nucleic acids

Nucleic AcidsInformation

storage

proteins

DNA

Nucleic Acids• Function:

– genetic material• stores information

– genes– blueprint for building proteins

» DNA RNA proteins• transfers information

– blueprint for new cells– blueprint for next generation

DNA RNA protein: information flow in a cell

1

2

3

Synthesis of mRNA in the nucleus

Movement of mRNA into cytoplasm via nuclear pore

Synthesisof protein

NUCLEUSCYTOPLASM

DNA

mRNA

Ribosome

AminoacidsPolypeptide

mRNA

Nucleic Acids• Examples:

– RNA (ribonucleic acid)• single helix

– DNA (deoxyribonucleic acid)• double helix

• Structure:– monomers = nucleotides

RNA

Nucleotides• 3 parts

– nitrogen base (C-N ring)– pentose sugar (5C)

• ribose in RNA• deoxyribose in DNA

– phosphate (PO4) group

Are nucleic acidscharged molecules?

Nitrogen baseI’m the

A,T,C,G or Upart!

SPECIAL NOTE

• A NUCLEOSIDE is a precursor to a NUCLEOTIDE. It contain ONLY a nitrogenous base and a sugar – NO PHOSPHATE

Types of nucleotides• 2 types of nucleotides

– different nitrogen bases – purines

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

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

Purine =PURE As Gold Pyrimidines=CUT the PY

Formation of a nucleic polymer

• DEHYDRATION SYNTHESIS AGAIN!!!!

• A bond forms between the adjoining nucleotides and is assisted by polymerases

• A backbone of S-P-S-P-S- etc. is formed

DNA Synthesis

1. A new strand of DNA is synthesized in the 5' to 3' direction

2. There a 3’ end must be open to elongate• NOTE: It is read by RNA from the 3’ to 5’ end

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

Breaking down into Monomers

• HYDROLYSIS AGAIN!!!• Bonds between the adjacent nucleotides are

destroyed within the nucleic acid polymer.

Pairing of nucleotides• Nucleotides bond between

DNA strands– H bonds– purine :: pyrimidine– A :: T

• 2 H bonds – G :: C

• 3 H bonds

Matching bases?Why is this important?

DNA molecule

• Double helix– H bonds between bases join

the 2 strands• A :: T• C ::: G

H bonds?Why is this important?

A brief, explanatory film strip

Copying DNA

• Replication– 2 strands of DNA helix are

complementary• have one, can build other• have one, can rebuild the whole

Matching halves?Why is this

a good system?

When does a cell copy DNA?• When in the life of a cell does DNA have to

be copied?– cell reproduction

• mitosis– gamete production

• meiosis

DNA replication“It has not escaped our notice that the specific pairing we have postulated immediately suggests a possible copying mechanism for the genetic material.”-James Watson & Francis Crick(1953)

Watson and Crick … and…1953 | 1962

Watson

Crick

Maurice Wilkins… and… 1953 | 1962

Rosalind Franklin (1920-1958)

X-ray crystallography X-ray

diffraction pattern

Photographic film

Diffracted X-rays

X-raysource

X-ray beam

Crystal Nucleic acid Protein

(a) X-ray diffraction pattern (b) 3D computer model

James Watson Describes the Moment

Interesting note…• Ratio of A-T:G-C

affects stability of DNA molecule– 2 H bonds vs. 3 H bonds– biotech procedures

• more G-C = need higher T° to separate strands

– high T° organisms• many G-C

– parasites• many A-T (don’t know why)

Another interesting note…• ATP

Adenosine triphosphate

++

modified nucleotide adenine (AMP) + Pi + Pi

You should now be able to:1. List and describe the four major classes of molecules2. Distinguish between the following pairs: pyrimidine and purine,

nucleotide and nucleoside, ribose and deoxyribose, the 5’ end and 3’ end of a nucleotide

Macromolecule Review

Carbohydrates • Structure / monomer

– monosaccharide• Function

– energy– raw materials– energy storage– structural compounds

• Examples– glucose, starch, cellulose, glycogen

glycosidic bond

Lipids • Structure / building block

– glycerol, fatty acid, cholesterol, H-C chains• Function

– energy storage– membranes– hormones

• Examples- fat, phospholipids, steroids

• NOT POLYMERS (No repeating units)ester bond (in a fat)

Proteins • Structure / monomer

– amino acids– levels of structure

• Function – enzymes u defense– transport u structure– signals u receptors

• Examples– digestive enzymes, membrane channels, insulin

hormone, actin

peptide bond

Nucleic acids

• Structure / monomer– nucleotide

• Function – information storage

& transfer• Examples

– DNA, RNA– Modified Nucleotide: ATP

phosphodiester bond