UNIT 2 - DNA & DNA REPLICATION

CH 7.1 & 7.2 P. 137-148

THE UNITS OF DNA

DNA is a polymer. The monomer units of DNA are

nucleotides, and the polymer is known as a "polynucleotide."

Each nucleotide consists of a 5-carbon sugar (deoxyribose), a nitrogen containing base attached to the sugar, and a phosphate group.

NUCLEOTIDES There are four different types of

nucleotides found in DNA, differing only in the nitrogenous base. The four nucleotides are given one letter abbreviations as shorthand for the four bases.

A is for adenine

G is for guanine

C is for cytosine

T is for thymine

Purine & Pyrimidine Bases Adenine and guanine are purines. Purines are the larger of the two types

of bases found in DNA. Cytosine and thymine are pyrimidines.

DNA BACKBONE

The DNA backbone is a polymer with an alternating sugar-phosphate sequence.

The deoxyribose sugars are joined to phosphate groups in ester links, also known as "phosphodiester" bonds. – Important bonds that can’t break

DNA DOUBLE HELIX DNA is a normally double stranded

macromolecule. Two polynucleotide chains, held together by weak hydrogen bonds, form a DNA molecule.– Note H-bonds are an attraction that can

pull apart and go back together relatively easily

P. 144 FIG 7-11 Also note the two strands run in

opposite directions

FEATURES OF THE DOUBLE HELIX The two polynucleotide chains run in opposite

directions The sugar-phosphate backbones of the two

DNA strands wind around the helix axis like the railing of a spiral staircase

The bases of the individual nucleotides are on the inside of the helix, stacked on top of each other like the steps of a spiral staircase.

SEE FIG 7-10 p. 143 in your TEXT BOOK

SO WHAT IS THE POINT? DNA is the brains of every cell because

it contains all of the genes that are the codes for making proteins

PURPOSE OF DNA

DNA has two major purposes– DNA REPLICATION

http://www.youtube.com/watch?v=rpwjZX_z5rg

– PROTEIN SYSNTHESIS

DNA REPLICATION Replication = when more cells need to

be produced, COMPLETE copies of the original DNA must be made – MITOSIS - nuclear division plus cytokinesis,

to produces two identical daughter cells for growth and development of an organism

– MEIOSIS - results in the production of gametes with only 1 set of DNA

(more details later!)

PROTEIN SYNTHESIS

Protein synthesis = when proteins are needed as enzymes that control all of the reactions in a cell, PARTIAL copies of a piece of DNA called a gene must be transcribed to be then translated into an amino acid polymer = protein = enzyme