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PowerPoint Lectures for Biology, Seventh Edition

Neil Campbell and Jane Reece

Lectures by Chris Romero

Chapter 17

From Gene to Protein

Basic Principles of Transcription and Translation

Transcription = DNA  mRNA

(mRNA = messenger RNA)

Translation = mRNA  polypeptide
Occurs on ribosomes

Basic Principles of Transcription and Translation

Transcription = DNA  mRNA

(mRNA = messenger RNA)

Translation = mRNA  polypeptide
Occurs on ribosomes

DNA  mRNA  polypeptide

Prokaryotes
Transcription and translation occur together

Figure 17.3a

Eukaryotes-
Transcription occurs in nucleus

Eukaryotes-
RNA transcripts are modified before becoming true mRNA

Eukaryotes-
Translation occurs in cytoplasm

Cellular chain of command
DNA RNA amino acid (protein)

Codons: Triplets of Bases

Codon

Codons: Triplets of Bases

Cracking the Code

Codon = 1. Translated into an amino acid

2. Serves as a translational start/stop signal

DNA sequences in gene:
CCTCAGAGTGTG
TACGTTGCGCCC

TRANSCRIPTION

RNA sequence = ?

TRANSLATION

Amino acid sequence = ?

Codons must be read in the correct reading frame
Ex: “The red dog ate the cat”
Change reading frame

“her edd oga tet hec at”

Concept 17.2: Transcription
DNA  RNA: a closer look

RNA synthesis

Catalyzed by RNA polymerase

1. Pries the DNA strands apart

2. Adds and Hooks together the RNA nucleotides

Synthesis of an RNA Transcript

3 stages of transcription:

1. Initiation

2. Elongation

3. Termination

1. Initiation

Initiation

2. Elongation

3. Termination

Synthesis of an RNA Transcript

Transcription Elongation

3 steps of transcription

1. Initiation –more specific in Eukaryotes
2. Elongation
3. Termination

Initiation of Transcription

Prokaryote Vs. Eukaryote Promoters:

Prok. = RNA Pol Bind to promoter sequence

Euk. = Transcription factors bind first to TATA box

 then RNA pol II binds

Concept 17.4

Translation = RNA directed synthesis of a polypeptide
mRNA  polypeptide

Translation
Takes place in the cytoplasm
Ribosome attaches to an mRNA
Codon mRNA message polypeptide by tRNA

tRNA- transfer RNA:

1. specific amino acid attachment site

2. base triplet called an anticodon on one end

ANTI-CODON

Amino acid attachment site

tRNA- transfer RNA:

1. specific amino acid attachment site

2. base triplet called an anticodon on one end

Anti-Codon?

Amino acid?

GGA

tRNA- transfer RNA:

1. specific amino acid attachment site

2. base triplet called an anticodon on one end

CCU

Glycine

GGA

Ribosomes have 2 subunits (small + large)

Hold the tRNA and mRNA close together during translation

Large Subunit

Small Subunit

tRNA binding sites

mRNA binding site

Building a Polypeptide

We can divide translation into three stages
Initiation
Elongation
Termination

Initiation

mRNA, tRNA, and ribosome subunits assemble

Elongation: step 1- codon recognition

Elongation: Step 2- peptide bond formation

Elongation:

Elongation: Step 3- translocation

Termination of Translation: Step 3

Ribosome reaches a stop codon in the mRNA

Release Factor

Concept 17.7

Mutations- changes in the genetic material of a cell
Point mutations
changes in just one base pair of a gene

Normal

Figure 17.23

Normal Point Mutation

Types of Point Mutations

Point mutations
Base-pair substitutions
Base-pair insertions or deletions

Substitutions

A base-pair substitution
Can cause missense or nonsense

Figure 17.24

Missense

Nonsense

Insertions and Deletions

Insertions and deletions
Are additions or losses of nucleotide pairs in a gene
May produce frameshift mutations

Figure 17.25

Review

Transcription: DNA  mRNA
Promoter, TATA box, Transcription factors, RNA Polymerase
Translation: mRNA  polypeptide
Small and Large ribosome subunits, mRNA, tRNA, amino acids, EPA sites

Review

Ch 17: Transcription and Translation
Transcription: 3 stages
Initiation, elongation, termination
mRNA processing
Translation : 3 stages
Initiation, elongation, termination
DNA mutations