4.18.24 Movement Legacies, Reflection, and Review.pptx
AP Biology Ch. 14 part 1 Transcription
1. Ch. 13 & 14
Anti - opposite
Intro - within
Muta - change
-script - to write
Helic - a spiral
Semi - half
Trans - across
Feb 17?
2. AP Biology Plans for the week of January 25th
through January
29th
, 2016
• Monday 1-25-16: Ch. 14 part 1 notes
• Tuesday 1-26-16: Ch. 14 part 2 notes
• Wednesday 1-27-16: big group diagram of transcription and
translation
• Thursday & Friday 1-28 & 1-29: Review and practice questions
for Ch. 13 and 14
Homework: Study Fig 14.24 on page 287 for a diagram quiz on MONDAY 2-1-16
3. Objectives
1. Identify and describe the 3 stages
of transcription
2. Describe how pre-mRNA is
altered to become functional
mRNA in eukaryotes
5. To aid in your notetaking…
Key vocabulary terms are in
orange, bold font and underlined
6. Overview of Concepts
1.1. The information in DNA is in theThe information in DNA is in the
sequence of nucleotidessequence of nucleotides
2.2. Transcription is the production of RNATranscription is the production of RNA
1.1. There are several types of RNAThere are several types of RNA
2.2. mRNA is the transcribed code for a proteinmRNA is the transcribed code for a protein
based on the DNAbased on the DNA
3.3. mRNA is modified in eukaryotic cellsmRNA is modified in eukaryotic cells
before it is functionalbefore it is functional
1.1. The information in DNA is in theThe information in DNA is in the
sequence of nucleotidessequence of nucleotides
2.2. Transcription is the production of RNATranscription is the production of RNA
1.1. There are several types of RNAThere are several types of RNA
2.2. mRNA is the transcribed code for a proteinmRNA is the transcribed code for a protein
based on the DNAbased on the DNA
3.3. mRNA is modified in eukaryotic cellsmRNA is modified in eukaryotic cells
before it is functionalbefore it is functional
8. RNA is the bridge between DNA
& proteins
There are some key differences between DNA & RNA
DNA RNA
Sugar -
deoxyribose
Sugar - ribose
Bases - A, T, C, G Bases - A, U, C, G
Double stranded
& very long
Single stranded &
shorter
9. To go from the DNA to proteins
requires 2 major steps:
Transcription & Translation
Transcription - DNA
to RNA
Translation - RNA to
protein
We will focus onWe will focus on
Transcription todayTranscription today
11. Why can’t we just go straight
from DNA to proteins?
Having a “middle-
man” in the form of
RNA protects the all
important DNA
It is more efficient -
many copies of that
gene can be made &
used simultaneously
12. Quick Think
What is transcription and why
is it important in the
synthesis of proteins?
13. Prokaryotes vs. Eukaryotes
Prokaryotes - both
transcription & translation
occur in the cytosol, since
there is no nucleus
These processes can happen
simultaneously
Eukaryotes - transcription
in nucleus, translation in
cytosol
14. The synthesis of mRNA
Messenger RNA is made
in much the same way
that DNA is replicated
The DNA strand serves as
a template for the linking
of complementary base
pairs
15. Quick Think
If DNA polymeraseDNA polymerase adds DNA
nucleotides to make a strand of
DNA
then
What enzyme do you suppose
adds RNA nucleotides to make a
strand of RNA?
16. RNA polymerase
This enzyme separates the DNA strands
It also bonds the RNA nucleotides
together
It attaches at a special sequence of
bases on the DNA called the promoter
region
17. The stretch of DNA that gets
transcribed is called the
transcription unit
This is the region of the DNA that
contains the information for
making the protein
18. The 3 stages of
Transcription
1. Initiation
2. Elongation
3. Termination
start
build
break-off
19. Initiation
In prokaryotesprokaryotes - RNA
pol recognizes the
promoter region and
binds directly to it
In eukaryoteseukaryotes - proteins
called transcription
factors attach to
promoter 1st, then RNA
pol attaches
An important promoter
sequence in eukaryotes is
called a TATA box
It contains the bases
TATAAAA
21. Elongation
RNA pol untwists the
DNA 10-20 bases at
a time
RNA strand is made
in the 5’ to 3’
direction, with new
bases added to the 3’
end
As it gets longer, it
peels away from the
DNA chain & the DNA
double helix reforms Several RNA pol can be working onSeveral RNA pol can be working on
the same gene at the same time,the same gene at the same time,
increasing the rate of transcriptionincreasing the rate of transcription
22. Termination
In prokaryotesprokaryotes -
RNA pol goes
through a
termination
sequence,
detaches, &
releases the
transcript.
The transcript is
available for
immediate use by
the cell
23. Question for ya
What are the 3 stages of
transcription
What happens at each stage?
24. Termination in EukaryotesEukaryotes
The pre-mRNA
strand is cut off
from the growing
RNA chain
RNA pol is still
attached to the DNA
and continues to
transcribe it
The mRNA is NOT
ready for use yet
25. Quick Think
What are some differences
between transcription in
prokaryotesprokaryotes versus eukaryoteseukaryotes?
26. Modification of the mRNA in
eukaryotes
In eukaryotic cells the
mRNA is modified before it
becomes functional
This is why it is called pre-
mRNA
In general, both ends of the
pre-mRNA are altered
Some of the middle parts
may be cut out and the
remains sliced together
27. Modification #1
The 5’ cap
A modified guanine nucleotide is
added
This is called the 5’ cap
29. Why???
The 5’ cap and the 3’ tail
help to:
Export mRNA from the
nucleus
Protect mRNA from
hydrolytic enzymes
Allow ribosomes to attach
at the 5’ end
The 5’ cap and the 3’ tail
help to:
Export mRNA from the
nucleus
Protect mRNA from
hydrolytic enzymes
Allow ribosomes to attach
at the 5’ end
30. Modification # 3
RNA splicing
In the DNA and RNA
there are long non-coding
regions between coding
regions
non-coding regions =
introns
coding regions = exons
RNA splicing removes the
introns & joins the exons
31. How does it know what to cut
out?
introns recognized by
spliceosomes (an type
of RNA + proteins)
spliceosomes cut out
the introns and fuse
the exons
32. Quick Think
What are some ways the RNA is
modified before it is translated in
eukaryotic cells?
33. Ribozymes
Ribozymes are RNA
molecules that function
as enzymes in the
splicing of RNA
Their discovery
eliminated the
hypothesis that all
enzymes were proteins
34. Why introns?
Allows for alternative RNA splicing to occur
Genes can code for more than one polypeptide
depending on which segments are treated as exons
during RNA splicing
Introns increase the likelihood of crossing over
(more places for it to occur if gene is longer)
Exons from different genes may get combined
Exon shuffling can lead to new proteins,
increasing genetic variation
35. Exit Ticket
How is the functional mRNA
different from the DNA template
that was used to produce it?
Think of as many differences as
you can. I can think of at least 7
differences.
36. Types of RNA polymerase
Only 1 type in
prokaryotes
Three types in
eukaryotes
RNA pol II is used
in the synthesis of
mRNA
RNA
polymerase
37. Termination in EukaryotesEukaryotes
The pre-mRNA
strand is cut off
from the growing
RNA chain
RNA pol is still
attached to the DNA
and continues to
transcribe it
RNA pol continues
much further down
the DNA and
eventually falls off