Molec. Genetics L.Os (Ch. 16)

• Students need to understand the basic structure of DNA. Look at Figure 16.7

• DNA replication is “semi-conservative” • DNA replication is facilitated by a host of

enzymes (Table 16.1 and Figure 16.6)• If time remains, teach “the road to the

Double Helix”

The Cell CycleYou are here

(in Chapter 16)

Watson and Crick (with a little help from Rosalind Franklin)

• Who they were…

• X-ray Crystalography (fig 16.6)…

What did Watson and Crick See in that Image?

What about the uniformity of the Double Helix?

Some more information

• Chargaff’s Rules:– Every organism…

– The Ratios of A-T and G-C

W & C also figured out that replication was “semi-conservative”

DNA is a…

Replication Up Close

5’

3’

Semi-Conservative Nature of DNA Replication

• What Does “semi-conservative” mean?

DNA Replication: The Players

• • • • • •

Leading Strand Replication

Important Point (see next slide)

Bacterial DNA Replication

Present Past

5’ to 3’

What About Bacteria ( )?

Molecular Genetics L.O.s (Ch 17)

• Jump right in on Page 311, Basic principles of transcription and translation. This is very straightforward. Students should know the basic components of the “Central Dogma of Molecular Biology”

• They should be able to read a sequence of DNA and write out the correct polypeptide using a genetic code chart.

– 2a) Transcription: DNA directed, and Protein mediated, synthesis of mRNA. Focus on the three main steps: Initiation, Elongation and Termination. Figure 17.7 is the essential figure here.

– 2b) mRNA splicing. Prokaryotes don’t splice mRNA, eukaryotes do splice mRNA. – 2c) Translation: RNA directed synthesis of a polypeptide. You’ll need a good

animation to teach this, I like: http://highered.mcgraw-hill.com/sites/0072437316/student_view0/chapter15/animations.html it’s simple, but get all the points across.

– 2d) Discuss the role of polyribsomes…a little bit of mRNA can go a long way. All protein synthesis starts in the cytosol, however…Fig 17.21

• Students need to be able to differentiate between silent mutations, mis-sense mutations and non-sense mutations.

DNA RNA PROTEIN

Examples of:

DNA RNA PROTEIN

Beadle and Tatum: worked with enzymatic pathways inNeurospora…(Fig 17.2)

They concluded…”one gene one enzyme”

It’s been modified to…one gene, one gene product…(unless you consider alternative gene splicing and gene regulation

DNA RNA PROTEIN

An overview:

“The Central Dogma”THE FLOW OF GENETIC INFORMATION

Why RNA?1. Protect the original copy!

(DNA)

2. Multiple RNA transcripts can be translated simultaneously

3. RNA can be edited and spliced, even shuffled, but you don’t want to make changes to the original copy.

How is the Genetic Code Deciphered?

How was the code cracked?

Central Dogma 1: Transcription

3 Key Terms:(I, E, T)

Central Dogma 1: Transcription (2)

10-20nucleotides

RNA polymerase60 nuc/sec!

Central Dogma 2: RNA Processing

Transcription ArithmeticAverage Primary Transcript: 8 kb (or 8000 bp)Average polypeptide is: 400 aaAverage processed mRNA that leaves the nucleus is:

How Does Splicing Occur?

The $64,000 Question: WHY INTRONS?

• Regulation of genetic expression

• Alternative RNA Splicing!, which means…

• 1 gene, multiple proteins

• Exon Shuffling!• Distance between exons

increases probability of recombining useful exons during meiosis.

Central Dogma 3: Translation

• The Players:

The Players: t-RNA

The Players: Ribosomes!

• r-RNA Rules!

• l-su

• s-su

Translation of polypeptides: 3 steps

• Initiation initiation factors• Elongation elongation factors• Termination release factors(the same as transcription)

Translation 1: Initiation

C

N

What becomes of polypeptides?

DNA

RNA

polypeptide

protein

protein modification

One view of “protein regulation”All proteins start of…

Role of RNA• messenger RNA --

• transfer RNA --

• ribosomal RNA --

• Primary Transcript --

• Small nuclear RNA (snRNA) --

• SRP RNA --

DNA RNA PROTEIN

Mutations

• Specifically point mutations…

• Base pair mutations– Silent

– Missense

– Nonsense

Examples of point mutations

Sickle Cell Anemia: a great example of missense

Insertions and deletions

• Much more devastating• Because they lead to…

• So what…

• Examples

Application of Gene to Protein and microbial genetics. Learning Objectives (Ch. 18)

• Bacteria have one chromosome, and speed of replication is of the essence. Speed of replication leads to mutation, and this provides raw material for natural selection.

• In addition to spontaneous mutation, genetic diversity of bacteria is caused by transformation, conjugation, transduction and transposition.

•  Although bacteria don’t have introns, they can control gene expression. The most basic way bacterial cells control gene expression is through operons. Students need to understand both inducible and repressible operons.

• Students should be familiar with different types of viruses. Focus on phages

and retroviruses.

The pGLO plasmid exploits a characteristic of bacterial DNA called (Inducible) operons

• An operon is…

• It consists of…

• But it’s under the Influence of…

Other operons are repressible

• Meaning…

• How do they work?

Key Similarities and Differences between three types of Operons

Type of Operon “Normal State” Regulatory

MechanismType of

Pathway

Reason for inclusion of

genome

Repressible

Inducible

Feedforward

p. 355

Operons are only part of the bacterial genome

• What else do we know about E. coli– Size/number of genes: 100kb; ≈ 4000 genes

• So what?– How E. coli packs the DNA into a into the cell:

• Supercoiling via isomerase, – How it replicates: binary fision (see ch. 16)– How fast it replicates: lab (optimal): 30 min – human colon (pretty darn optimal): every 12-

24 hours

A quick look at Binary Fission

Question: If mutation is the raw material for natural selection, where do the mutations happen?

Answer: virtually anywhere

So what?

New mutations, though individually rare, can significantly increase genetic diversity (of a population) when reproductive rate is very high. This diversity, in turn, affects the evolution of bacterial populations…

because individuals who are genetically equipped for a local environment will reproduce more prolifically than other, less fit individuals.Increases genetic diversity in a constantly changing environment

and…

Increases genetic diversity in an assexually reproducing organism

What are other sources of genetic diversity?

Genetic Recombination!– Transformation

– Transduction

– Conjugation and Plasmids• (F plasmids and R plasmids)

– Transposition

Transduction• The virus is the vector!

• How can bacteria defend against viral (phage) attack?

Conjugation: Plasmid Transfer

• F+ Cells = • Hfr Cells = • R Cells =

Transposition: the movement of genes within a genome

How?

Why?

So what?Have genes, will travel

Amp-rStrep -r

Chl

oram

- r

Amox-r

Kan-r

Transposition and conjugation are theMolecular underpinning for rapid evolutionOf antibiotic resistant bacteria.

The Lowdown on Ch. 19• Most control is PRE-TRANSCRIPTIONAL! I tell my students, if it’s

transcribed, it’s likely to be translated…that wastes energy if the protein isn’t needed (Fig 19.3)

• Genomic control happens on the chromatin level thanks to histone proteins If the histones are wrapped tightly (methylated), the genes are likely to be “locked down”. If the histones are loose (acetylated), then genes are likely to be open for transcription (Figs 19.2 and 19.4)

• Intron and exon splicing adds to control of gene expression (Fig 19.5)

• Distal control elements and transcription factors interact with promoter regions to control gene expression. Bottom line, eukaryotic genomes are bigger, more complicated and have more complex promoter regions. (See Figure 19.6)