Transcript AP Biology Discussion Notes wed 1 14x

AP Biology Discussion Notes
Wednesday 01/14/2015
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
Things to DO:
1. Look over material before the next class
–
Write down thoughts, connections or questions
2. Read the chapter
– even when not “assigned”
3. Watch Videos about topics
– even when not assigned
4. Start reviewing topics from last semester
– Tie them to topics this semester and write
down connections or questions
5. ASK QUESTIONS
When DNA replicates, each
strand of the original DNA
molecule is used as a
template for the synthesis of
a second, complementary
strand. Which of the
following figures most
accurately illustrates
enzyme-mediated synthesis
of new DNA at a replication
fork?
Go to our website and
enter your best answer
to this question, then
complete the question of
the day
Question of the Day 1/14
• Draw a replication bubble label the
Following:
– leading strands
– lagging strands
– 5’ and 3’ ends on the new and template DNA
– Origin of replication
– Replication fork
Figure 16.15a
Leading
strand
Overview
Origin of replication
Lagging
strand
Primer
Lagging
strand
Overall directions
of replication
Leading
strand
When DNA replicates, each
strand of the original DNA
molecule is used as a
template for the synthesis of
a second, complementary
strand. Which of the
following figures most
accurately illustrates
enzyme-mediated synthesis
of new DNA at a replication
fork?
Go to our website and
enter your best answer
to this question, then
complete the question of
the day
Are there any choice
we could eliminate
right away?
(Sometimes its best to play
the……which of these is not
like the other game……look
at the differences and
similarities in each picture.)
Two KEY pieces of
information:
1. DNA strands are
ANTIparallel, and
therefore should be built in
opposite directions.
2. There is a lagging and a
leading strand because of
the directionality of DNA
Polymerase (that it can
only build new strands in
the 5’ to 3’ direction
Are there any choice we could eliminate
right away?
There would be 2 ways to eliminate 2
choices!
1. Both A & B show the leading strand
(
) and lagging strand (
) built in the same
direction, but they are built in
opposite directions, so you can
eliminate both A & B.
Are there any choice we could eliminate
right away?
2.A & C both show 2 strands being built
continuously. However, during DNA
replication there is a leading & lagging
strand produced. The lagging strand is
built discontinuously in pieces, and is
later connected by the enzyme Ligase.
This information allows us to eliminate
both A & C.
Are there any choices we could
eliminate right away?
Eliminating choices where strands are
built in the same direction and choices
that contain only leading strands (no
lagging strand) leaves us with only 1
choice, D.
D is built in two different directions, and has 1 lagging and 1 leading
strand.
The other key piece of information contained in this question is that
DNA polymerase can only build in the 5’ to 3’ direction. Meaning the
strand that it will build runs 5’ to 3’ and the strand that it is copying will
run 3’ to 5’. Only the directionality of the template strand is shown,
leaving you to infer that the other strand is opposite (anti-parallel).
Directionality of Template strand
3’
Directionality of New strands
5’ 3’
5’
Directionality of Template strand
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 virus
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
Double Helix Discussion
Double Helix Discussion
• Linus Pauling
Double Helix Discussion
Double Helix Discussion
• Impressions of Watson
Reminder
• DNA Assignment DUE FRIDAY