transcription

DNA RNA

translation

protein

Protein Synthesis

URACIL (U)base with a single-ring structure

phosphate group

sugar (ribose)

DNA

DNA

RNA

DNA

G C A T

C G T A

G C A U

G C T A

base-pairingduring DNAreplication

base-pairingduringtranscription

sugar-phosphate backbone of one strand of nucleotides in a DNA double helix

sugar-phosphate backbone of the other strand of nucleotides

part of the sequence of base-pairs (blue)

RNA polymerase, the enzyme that catalyzes transcription

DNA

transcribed DNA winds up again DNA to be transcribed unwinds

newly forming RNA transcript

DNA template at the assembly site

Transcription

3’5’

growing RNA transcript

5’

3’ 5’

3’

direction of transcription

Transcription

mature mRNA transcript

5’ 3’

3’

poly-A tail

5’

snipped out snipped out

cap

transcription into pre-mRNA

unit of transcription in a DNA strand

exon intron exon exonintron3’ 5’

base sequence of gene region

mRNA

From DNA to RNA

G ATACCAATAACCAC

C UAUGGUUAUUGGUG

From Codons to Amino AcidsC G G G G G U UUUU U U AA

arginine glycine tyrosine tryptophan tyrosine

codon in mRNA

anticodon

amino acid OH

amino-acidattachment site

Codon-tRNA-Amino Acid

small ribosome subunit large ribosome subunit

tunnel

intact ribosome+

Ribosomes

mRNA transcript

intact ribosome

Initiation

initiator tRNA

small ribosomal subunit

binding site for mRNA

(first binding site for tRNA)

(second binding site for tRNA)

platform on small ribosomal subunit

Elongation

Translation

ElongationTranslation

Termination

mRNA

new polypeptide chain

mRNA

original base triplet in a DNA strand

During replication, proofreading enzymes make a substitution:

a base substitution within the triplet (red)

original, unmutated sequence

a gene mutation

possible outcomes:

or

mRNA parental DNA amino acids

altered mRNA

DNA withbase insertion

altered amino-acid sequence

arginine glycine tyrosine tryptophan asparagine

arginine glycine leucine glutamateleucine

Mutations

mRNA rRNA tRNA

Translation

amino acids, tRNAs, ribosomal subunits

mRNA transcripts

protein subunits

ribosomal subunits

tRNA

Transcription

Protein