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 Leading strand Lagging strand Overall directions of replication 1 2

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. Conjugation Sort of like Bacterial 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 Viruses Only 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 Living 1.Attach to a “host” cell (animal, plant, or bacterium—virus = bacteriophage) 2.Injects its nucleic acid into the host 3.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 DNA 5.Host is now “re-programmed” to make viruses 6.Host cell blows up because it can’t hold all of the baby viruses—this is called LYSIS 7.This is the LYTIC CYCLE of a virusLYTIC CYCLE

The Lytic Cycle of a (bacterio)Phage

We all go Retro, eventually !

Bacterial Enemies A 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 DNA The 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 Insulin Human Growth Hormone Roundup-Ready Crops

Questions

DNA assignment