Nucleic acids:– Deoxyribonucleic acid (DNA)– Ribonucleic acid (RNA)

Monomers: ‘Nucleotide’– 5-carbon sugar (ribose or deoxyribose)– Phosphate group– Nitrogen base (cytosine, guanine, thymine,

cytosine)

Phosphorus• Sugar-Phosphate backbone

Nitrogen base pairs with the complementary base

Double Helix

Base pairing rules:– G pairs with C– T with A

Same structure except:– 5-carbon sugar is ribose– Uracil replaces thymine – Single stranded, not

double stranded

Types– mRNA (messenger)– rRNA (ribosomal)– tRNA (transfer)

Segments of DNA contain genes

Genes • information to code for

the production of polypeptides

• on the surface of the ribosome.

Before a proteins can be built: – DNA must undergo replication

–Helicase separates the strands of DNA–DNA polymerase assembles the nucleotides

Occurs during Interphase• S-Phase

Replicate this strand of DNA– AAGCCGTTA

–Animation

Information from DNA must be transported to the ribosomes

DNA unwinds and is copied by RNA– mRNA

mRNA moves out of the nucleus (pores) and attaches to the ribosomes

Transcribe this stretch of DNA– AAA TGC

•Animation•Animation II

Pre-mRNA will lose non-coding sequences called introns– ‘junk DNA’

Information codes for polypeptide (protein)– Exon

Amino acids • assembled on the surface of a

ribosome

Amino acids • tRNA binds an amino acid• In cytoplasm

tRNA bonds with sequences in the mRNA• codons– anticodon on tRNA bonds with

codon on mRNA

The codon sequences of mRNA may be translated into amino acids using the genetic code

Always read from the mRNA!

Translate: • AUG CAC GUU GGU

•Animation

A single stand of mRNA can produce hundreds of the same polypeptide in a short period of time.