Fig. 12-2, p.187

Fig. 12-5, p.190

Fig. 12-6, p.191

2-nanometer diameter overall

0.34-nanometer distancebetween each pair of bases

3.4-nanometerlength of eachfull twist of thedouble helix

In all respects shown here, theWatson–Crick model for DNAstructure is consistent with theknown biochemical and x-raydiffraction data.

The pattern of basepairing (A with T,and G with C) isconsistent with theknown compositionof DNA (A = T,and G = C).

Fig. 12-7, p.192

Fig. 12-8, p.192

new

newold

old

Fig. 12-9, p.193

Any gaps between basesof the “new” DNA are joinedto form a continuous strand.The base sequence of eachhalf-old, half-new DNAmolecule is identicalto that of the parent.

Part of a parentDNA molecule, with twocomplementary strands ofbase-paired nucleotides.

Replication starts.The strands are unwoundat many sites alongthe molecule’s length.

Each of the two parentstrands guides the assemblyof new DNA strands from freenucleotides, according tobase-pairing rules.

Fig. 12-10, p.194

Fig. 13-2, p.198

Fig. 13-3, p.198

Fig. 13-3, p.198

Fig. 13-3, p.198

gene region

RNA polymerase, the enzymethat catalyzes transcription

DNA templateunwinding

newly formingRNA transcript

DNA templatewinding up

Fig. 13-3, p.198

Table 13-1, p.199

Fig. 13-5, p.200

Fig. 13-7, p.201

amino acidattachment site

anticodon

Fig. 13-8, p.202

mRNA

initiatortRNA

smallribosomalsubunit

largeribosomalsubunit

Initiation

A mature mRNAleaves the nucleusand enters cytoplasm,which has many freeamino acids, tRNAs,and ribosome subunits.An initiator tRNA bindsto a small ribosomalsubunit and the mRNA.

A large ribosomalsubunit joins, and thecluster is now calledan initiation complex.

Fig. 13-8, p.202

A peptide bondforms between thesecond and thirdamino acids (here,valine and leucine).

A peptide bondforms between thefirst two amino acids(here, methionineand valine).

An initiator tRNAcarries the amino acidmethionine, so the firstamino acid of the newpolypeptide chain will be methionine. A second tRNA binds the second codon of the mRNA (here, thatcodon is GUG, so thetRNA that binds carriesthe amino acid valine).

Elongation

The first tRNAis released and theribosome moves tothe next codon in themRNA. A third tRNAbinds to the thirdcodon of the mRNA(here, that codon isUUA, so the tRNAcarries the aminoacid leucine).

Fig. 13-8, p.202

A peptide bondforms between thethird and fourthamino acids(here, leucineand glycine)

The second RNAis released and theribosome moves to the next codon. A fourth tRNA binds the fourth mRNA codon (here, that codon is GGG, sothe tRNA carries the amino acid glycine).

Steps d and e are repeated over and over until the ribosome encounters a STOP codon in the mRNA. The mRNA transcript and the new polypeptide chain are released from the ribosome. The two ribosomal subunits separate from each other. Translation isnow complete. Either the chain will join the pool of proteins in the cytoplasm or it will enter rough ER of the endomembrane system (Section 4.8).

Termination

Fig. 13-9, p.202

THREONINE PROLINE GLUTAMATE GLUTAMATE LYSINE

THREONINE PROLINE GLUTAMATE LYSINE

THREONINE PROLINE ARGININEGLYCINE

VALINE

deletionin DNA

part of DNA

mRNA transcribedfrom DNA

resulting aminoacid sequence

base substitutionin DNA

altered mRNA

altered aminoacid sequence

altered aminoacid sequence

altered mRNA

Fig. 13-11, p.206

mRNA

Final protein

cytoplasmicpools ofamino acids,ribosomalsubunits,and tRNAs

Convergenceof RNAs

Transcription Assembly of RNA on unwound regions of DNA molecule

At an intactribosome,synthesis ofa polypeptidechain at thebinding sitesfor mRNAand tRNAs

Translation

mRNAprocessing

maturetRNA

ribosomalsubunits

mature mRNAtranscripts

proteins

tRNArRNA