Download File - Ms. Poole`s Biology

Agenda 3/13
• Transcription Notes
• Transcription Posters/RNA Processing
• Turn in: Worksheets from Friday
• Homework: Transcription video and notes,
Chp 14 reading/notes
1
Warm Up (In Notes)
• Create a list of 10 specific proteins we
have studied this year
2
Uses of Proteins
3
What is a gene?
• Today the definition for a gene is a
sequence of DNA molecules that can
direct the synthesis of a molecule product.
• Genes do not all code for a protein, but all
do code for an RNA molecule.
• Some of those RNAs are translated into
protein, but many serve other functions,
such as gene regulation.
4
Overview of Protein Synthesis
• DNA is located in the nucleus
• Proteins are made in the cytoplasm
• RNA is the intermediate between the DNA code
and the actual synthesis of a protein
5
Structure of RNA versus DNA
6
• RNA vs. DNA
• RNA
DNA
• Single stranded
Double stranded
• Ribose
Deoxyribose
• U instead T
T instead of U
• Nucleus and cytoplasm
organelles
Restricted to nucleus &
• Multiple uses
Used as template for
RNA synthesis and proteins
7
Three Main Types of RNA
8
There are different types of RNA
• mRNA-carries the information from the DNA gene to the
cytoplasm. Determines the sequence of amino acids for a protein
• tRNA-brings the correct amino acid to the ribosome and mRNA in
translation
• rRNA-found on ribosomes and used to "connect" the tRNA to the
mRNA
• snRNA-found on spliceosomes. Used to remove introns.
• SRP RNA-part of the signal recognition particle used to bring a
translating ribosome to the E.R. and threads the emerging
polypeptide chain into the lumen of the E.R.
9
Differences in Protein Synthesis between
Prokaryotes and Eukaryotes
• Prokaryotes do not have introns like
eukaryotes.
• RNA in prokaryotes does not have to
be processed like eukaryotes.
• Transcription and translation can be
simultaneous in prokaryotes.
10
Genetic Code
• Amino acids
are coded for
by a triplet of
DNA
nucleotides
called a codon.
11
• Come up with 3 different observations
about the codon chart
12
Genetic Code
•
The code has redundancy
(What does this mean?
•
Each codon only codes
for one amino acid.
•
The code is a universal
code meaning almost all
cells use the same code.
A eukaryotic gene can be
expressed in a
prokaryotic cell.
13
Specifying or Coding for a Polypeptide
This gene designates that the following
peptide chain be made with the amino acids
in this particular order.
14
Transcription
Overview
Transcription-RNA
synthesis from a
DNA template
• 1. Initiation
• 2. Elongation
• 3. Termination
• (4?) RNA
processing
15
Initiation
There is a region prior to beginning of a gene
where the RNA polymerase attaches called the
promoter region.
The promoter region determines which side of the
gene will be transcribed.
In a prokaryotic cell, the RNA polymerase attaches
directly to the region
In a eukaryotic cell there are transcription factors
(proteins) which help facilitate the attachment of
the RNA polymerase.
16
Initiation
17
Elongation
• Elongation- RNA polymerase unwinds the
DNA and base pairs RNA nucleotides to
the DNA gene. RNA is made 5′ → 3′ so
the DNA gene is 3′ → 5′.
18
Termination
RNA synthesis proceeds
until the RNA
polymerase encounters
a sequence that triggers
its dissociation.
19
RNA Processing
Eukaryotic RNA processing
• 5' cap is added.
• At the 3' end 30-200 adenine nucleotides are added
(poly-A-tail).
• Introns are removed
20
Removing Introns
•
A spliceosome
removes the introns.
•
Spliceosomes are
composed of smaller
particles called snRNP
(made of proteins and
snRNA).
•
The spliceosome will
splice the intron at a
specific RNA
sequence.
21
RNA Processing
• Different exons are recombined in different ways
for certain mRNAs. This increases the number
of different proteins.
22
Exon Shuffling and Different Proteins
•
Proteins often have a
modular architecture
consisting of discrete
regions called domains
•
In many cases, different
exons code for the
different domains in a
protein
•
Exon shuffling may result
in the evolution of new
proteins.
23
Ready for Translation
• This mRNA has been processed and is
called mature mRNA. It is ready to go to
the cytoplasm for translation.
24
Transcription Posters
• Using the template DNA strand and RNA
nucleotides, create your strand of mRNA. On your
poster also include:
–
–
–
–
Three steps of transcription
The promoter region
Draw and label all enzymes involved
Depict RNA processing incorporating terms from the
reading
25