AP Biology Discussion Notes

Thursday 1/28/2016

Goals for Today• Be able to describe how bacteria increase

their genetic variation

• Be able to describe the “life” cycle of a virus

• Be able to describe the difference between a virus and a retrovirus

• Be able to describe a restriction enzyme, where it comes from, and what its potential uses are

Question of the Day 1/28

• In what direction does the leading strand travel relative to the replication fork?

Figure 16.16a

Origin of replication

Overview

Leadingstrand

Leadingstrand

Laggingstrand

Lagging strand

Overall directionsof replication

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Bacteria• Prokaryotic• Circular DNA (couple million B.P.)• Teeny “satellite” pieces of DNA called

PLASMIDS (thousands of BP)• Not much for organelles• Cell wall that can be trashed by

antibiotics–Penicillin, amoxicillin, ampicillin

How Do Bacteria Get Their DNA Changed NATURALLY?

1. ConjugationSort of likeBacterial sex

Sex Pilus(plural=pili)--plasmid transfer

How Do Bacteria Get Their DNA Changed?

What scientist showed that traits from One bacteria could be transferred to another?

What other scientist and his team showed the material responsible for that transformation was DNA?

2. Transformation—bacteria takes in some DNA from its environment

3. Transduction—a virus carries some DNA from one bacterium to another

Characteristics of VirusesOnly two parts to them:

--a protein outer coat--either some DNA or some RNA

RNA viruses are also known as “retroviruses” (more on this later)

How Viruses Make Their Living1. Attach to a “host” cell (animal, plant, or bacterium

—virus = bacteriophage)2. Injects its nucleic acid into the host3. If it’s an RNA virus, then it also injects “Reverse

Transcriptase” along with the RNA.4. Viral N.A. integrates itself into the host’s DNA5. Host is now “re-programmed” to make viruses6. Host cell blows up because it can’t hold all of the

baby viruses—this is called LYSIS7. This is the LYTIC CYCLE of a virus

The Lytic Cycle of a (bacterio)Phage

We all go Retro, eventually!

Bacterial EnemiesA bacterium’s nastiest natural enemy is

a bacteriophage (a virus)In the 1970’s, it was discovered that

bacteria had defense systems against viruses

These defense molecules are called Restriction Enzymes

Restriction Enzymes(also called Restriction Endonucleases)

Special enzymes produced by bacteria (NOT BY HUMANS!!!)

They snip/cut DNA at specific base sequences

Cut up DNA = harmless DNAThe bacteria wins (maybe)

How important are restriction enzymes?

The Nobel Prize in Physiology or Medicine 1978

Werner Arber Daniel Nathans Hamilton O. Smith

Recombinant DNA“Splicing” the DNA from one organism into the

DNA of another organism.The “new” DNA now has the ability to code for

“new” proteins.Some examples:Human InsulinHuman Growth HormoneRoundup-Ready Crops

Questions

DNA assignment