1. DNA, RNA structure 2. DNA replication 3. Transcription, translation

1. DNA, RNA structure

2. DNA replication

3. Transcription, translation

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

• DNA is a nucleic acid, made of long chains of nucleotides

DNA and RNA are polymers of nucleotides

Nucleotide

Phosphate group

Nitrogenous base

Sugar

Polynucleotide Sugar-phosphate backboneDNA nucleotide

Phosphategroup

Nitrogenous base(A, G, C, or T)

Thymine (T)

Sugar(deoxyribose)


• DNA has four kinds of bases, A, T, C, and G

Pyrimidines

Thymine (T) Cytosine (C)

Purines

Adenine (A) Guanine (G)


• RNA is also a nucleic acid– different sugar– U instead of T– Single strand, usually

Phosphategroup

Nitrogenous base(A, G, C, or U)

Uracil (U)

Sugar(ribose)


• Hydrogen bonds between bases hold the strands together: A and T, C and G

Ribbon model Partial chemical structure Computer model

Hydrogen bond


Untwisting and replication of DNA • each strand is a template for a new

strand

helicase

DNA polymerase


• Each strand of the double helix is oriented in the opposite direction

5 end 3 end

3 end 5 end

P

P

P

PP

P

P

P


• DNA polymerase works in only one direction

5 end

P

P

Parental DNA

DNA polymerasemolecule

53

35

35

Daughter strandsynthesizedcontinuously

Daughter strandsynthesizedin pieces

DNA ligase

Overall direction of replication

53

• Telomere sequences are lost with each replication.

• Cancer, aging

telomeres


– The DNA is transcribed into RNA, which is translated into the polypeptide

DNA

RNA

Protein

TRANSCRIPTION

TRANSLATION

• The information constituting an organism’s genotype is carried in its sequence of bases


Transcription produces genetic messages in the form of mRNA

RNApolymerase

RNA nucleotide

Direction oftranscription

Newly made RNA

Templatestrand of DNA


• In transcription, DNA helix unzips

– RNA nucleotides line up along one strand of DNA, following the base-pairing rules

– single-stranded messenger RNA peels away and DNA strands rejoin

– occurs in nucleus

RNA polymerase

DNA of gene

PromoterDNA Terminator

DNAInitiation

Elongation

TerminationGrowingRNA

RNApolymerase

Completed RNA


• The “words” of the DNA “language” are triplets of bases called codons– The codons in a gene specify the amino

acid sequence of a polypeptide

Translation of nucleic acids into amino acids


• An exercise in translating the genetic code

Startcodon

RNA

Transcribed strand

StopcodonTranslation

Transcription

DNA

Polypeptide


• In the cytoplasm, a ribosome attaches to the mRNA and translates its message into a polypeptide

• The process is aided by transfer RNAs

Transfer RNA molecules serve as interpreters during translation

Hydrogen bond

Amino acid attachment site

RNA polynucleotide chain

Anticodon


• Each tRNA molecule has a triplet anticodon on one end and an amino acid attachment site on the other

Anticodon

Amino acidattachment site


• The sequence of codons in DNA spells out the primary structure of a polypeptide– Polypeptides form proteins that cells and

organisms use

Review: The flow of genetic information in the cell is DNARNAprotein


• Mutations are changes in the DNA base sequence– caused by errors in DNA replication or by

mutagens

Mutations can change the meaning of genes


• Types of mutations

mRNA

NORMAL GENE

BASE SUBSTITUTION

BASE DELETION

Protein Met Lys Phe Gly Ala

Met Lys Phe Ser Ala

Met Lys Leu Ala His

Missing

Documents

1. DNA, RNA structure 2. DNA replication 3. Transcription, translation