Macromolecules Part IV:

Nucleic Acids

Informational molecules

Introduction: Nucleic Acids The amino acid sequence of a polypeptide

is programmed by a gene A gene consists of regions of DNA, a

polymer of nucleic acids (100’s to 1000’s) DNA (and their genes) is passed by the

mechanisms of inheritance Only molecule that can produce identical

copies of themselves

There are two types of nucleic acids: ribonucleic acid (RNA) deoxyribonucleic acid (DNA)

DNA provides direction for its own replication

DNA also directs RNA synthesis and, through RNA, controls protein synthesis

Nucleic acids store and transmit hereditary information

Roles of DNA Protein expression (Phenotypes) Inheritance (Genotypes)

3.Evolution (Mutations)

Nucleotides Nucleic acids are

polymers of monomers called nucleotides

Each nucleotide consists of three parts: a nitrogen basea pentose sugara phosphate group

Sugar-Phosphate “Backbone”

Nucleic Acids Polynucleotides are synthesized by

connecting the sugars of one nucleotide to the phosphate of the next with a phosphodiester link

The phosphodiester links create a repeating backbone of sugar-phosphate units with the nitrogen bases as appendages

RNA

DNA

Phosphodiester link

Nucleotides The nitrogen bases, rings of carbon and

nitrogen, come in two types: Purines pyrimidines

Pyrimidines have a single six-membered ring The three different pyrimidines that differ in the

atoms attached to the ring: cytosine (C), thymine (T), and uracil (U)

Purines have a six-membered ring joined to a five-membered ring and there are two types: adenine (A) and guanine (G)

Purine BasesPurine Bases Adenine and guanine are purinesAdenine and guanine are purines Purines are the larger of the two types of bases Purines are the larger of the two types of bases

found in DNAfound in DNA

Pyrimidine BasesPyrimidine Bases

Cytosine, uracil and thymine are pyrimidinesCytosine, uracil and thymine are pyrimidines Mnemonic: Pyramids CUTMnemonic: Pyramids CUT

Because of their shapes, only some bases Because of their shapes, only some bases are compatible with each otherare compatible with each other

Purines always pair with pyramidinesPurines always pair with pyramidines Adenine (A) always pairs with thymine (T) (in Adenine (A) always pairs with thymine (T) (in

RNA, Adenine pairs with Uracil RNA, Adenine pairs with Uracil (U)(U)) ) Guanine (G) with cytosine (C)Guanine (G) with cytosine (C)

Nucleotide Bases Nucleotide Bases PairingsPairings

Counting Carbons

Nucleosides VS. NucleotidesNucleosides VS. Nucleotides A nucleoside is one of the four A nucleoside is one of the four

DNA bases covalently attached DNA bases covalently attached to a sugarto a sugar

Nucleosides differ from Nucleosides differ from nucleotides in that they lack nucleotides in that they lack phosphate groupsphosphate groups

A nucleotide is a nucleoside A nucleotide is a nucleoside with one or more phosphate with one or more phosphate groups covalently attached to groups covalently attached to the sugar groupthe sugar group

Step 1: Base

Step 2: Nucleoside

Step 3: Nucleotide

RNA RNA is made

by copying DNA and is used to make proteins

It is a SINGLE strand of nucleotides

DNA1. Take two nucleic

acid strands

2. Flip one of the strands

3. Line the strands together so that they bond

4. Twist them

5. Now you have DNA!

DNA: Double Helix Structure• DNA has a double helix structure with two strands that are antiparallel so that nucleotides can form hydrogen bonds

One Strand One Strand

H-Bonds

But why is it important that the strands are H-bonded and not covalently bonded?

Why H-bonds? In order to replicate, the strands

must separate to make new DNA strands (cannot be broken if the strands were covalently bound)

The sugar-phosphate backbones of the two polynucleotides are on the outside of the helix

Pairs of nitrogenous bases, one from each strand, connect the polynucleotide chains with hydrogen bonds

Most DNA molecules have thousands to millions of base pairs

Recap: What are the base-pair rules? Adenine (A) always pairs with thymine (T) (in

RNA, Adenine pairs with Uracil (U)) Guanine (G) with cytosine (C)

With these base-pairing rules, if we know the sequence of bases on one strand, we know the sequence on the opposite strand

The two strands are complementary

Nucleotide Bases Pairings

DNA - Base pairingDNA - Base pairing

Adenine and Thymine Adenine and Thymine always bind togetheralways bind together

Guanine and Guanine and Cytosine always bind Cytosine always bind togethertogether

Result: Double Helix Structure

An RNA molecule is single polynucleotide chain while DNA molecules have two polynucleotide strands that spiral around an imaginary axis to form a double helix

The pentose joined to the nitrogen base is ribose in nucleotides of RNA and deoxyribose in DNA

Nitrogen bases - thymine is replaced by uracil

What’s the difference between RNA and DNA?

ATP (adenosine triphosphate)

ATP is a nucleotide that is used to provide energy in cells

NAD+ and FAD These are nucleotide-containing molecules

that function as electron carriers in a variety of cellular processes.

NAD+ - nicotinamide adenine dinucleotide

FAD- flavin adenine dinucleotide

Home work

Study the table on page 30

Do Question on page 31 Questions1-12

Macromolecules Quiz Next Thursday 15th for day 1 classes and Friday 16th for day 2 classes