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Cell Signaling to Transcription
and Translation
Biology 160
We started by trying to understand this:
http://www.youtube.com/watch?v=VAhM9OxZDkU&NR=1
Figure 5.11
The Role of Membranes in
Cell Signaling
Watch Neutrophil explanation:
http://www.youtube.com/watch?v=OWUmXx5V_wE
Watch XVIVO animation:
http://www.youtube.com/watch?v=Mszlckmc4Hw
Want the longer version? Check out:
http://multimedia.mcb.harvard.edu/media.html
Click on “Inner Life: Animation”
Intro to the Immune System
Switch to Microbe Detectives
presentation
So how do microbes
cause B cells and T cells
to grow and divide?
Each cell has a receptor on its
cell surface that recognizes a
specific part of a microbe.
That receptor triggers a
Signal transduction pathway.
This triggers gene expression
(transcription) that…
…leads to protein synthesis
(translation) that…
…allows the cell to grow
(duplicate all its proteins that
help to duplicate all its organelles)
and divide (mitosis).
Watch cell signaling video
OK, so let’s
go into the
nucleus
and remind
ourselves
about DNA
structure
DNA Structure
DNA vs RNA Structure
– The four nucleotides found in DNA
• Differ in their nitrogenous bases.
• Are thymine (T), cytosine (C), adenine (A), and
guanine (G).
– RNA has uracil (U) in place of thymine.
– The model of DNA is like a rope ladder
twisted into a spiral.
– Detailed representations of DNA
• Notice that the bases pair in a complementary
fashion.
The Flow of Genetic Information
from DNA to RNA to Protein
– DNA functions as the inherited directions
for a cell or organism.
Copyright © 2007 Pearson Education, Inc. publishing as Pearson Benjamin Cummings
How an Organism’s Genotype
Produces Its Phenotype
– An organism’s genotype, its genetic
makeup, is the sequence of nucleotide
bases in DNA.
• The phenotype is the organism’s specific traits
(or what it looks like and how it functions),
which arise from the actions of a wide variety of
proteins.
Copyright © 2007 Pearson Education, Inc. publishing as Pearson Benjamin Cummings
– The one gene–one polypeptide hypothesis
states that the function of an individual
gene is to dictate the production of a
specific polypeptide.
From Nucleotides to Amino
Acids: An Overview
– Genetic
information in
DNA is
transcribed into
RNA and then
translated into
polypeptides.
Transcription: From DNA to RNA
http://www.youtube.com/watch?v=WsofH466lqk
– In transcription,
• Genetic information is transferred from DNA to
RNA.
• An RNA molecule is transcribed from a DNA
template.
– Transcription of an entire gene
Initiation of Transcription
– The “start
transcribing” signal
is a nucleotide
sequence called a
promoter.
– The first phase of
transcription is
initiation:
• RNA polymerase
attaches to the
promoter.
• RNA synthesis
begins.
RNA Elongation
– The second phase
of transcription is
elongation:
• The RNA grows
longer.
Termination of Transcription
– The third phase of
transcription is
termination:
• RNA polymerase
reaches a
sequence of DNA
bases called a
terminator.
The Processing of Eukaryotic RNA
– The eukaryotic cell
processes the RNA
after transcription.
– RNA processing
includes:
• Adding a cap and
tail
• Removing introns
• Splicing exons
together
Translation: The Players
– Translation
• Is the conversion from the nucleic acid
language to the protein language.
– The Players
• mRNA
• tRNA
• Ribosome
Messenger RNA (mRNA)
– What are the rules
for translating the
RNA message into
a polypeptide?
– Triplets of bases
• Specify all the
amino acids.
• Are called codons.
The Genetic Code
– The genetic code is shared by all organisms.
A firefly gene expressed
in a plant!!!
– An mRNA molecule also has a cap and tail
that help it bind to the ribosome.
Transfer RNA (tRNA)
– tRNA
• Acts as a
molecular
interpreter.
• Carries amino
acids.
• Matches amino
acids with codons
in mRNA using
anticodons.
Ribosomes
– Ribosomes
• Are organelles
that actually
make
polypeptides.
• Are made up
of two protein
subunits.
• Contain
ribosomal
RNA (rRNA).
•http://www.youtube.com/watch?v=5bLEDd-PSTQ&feature=related
•http://www.youtube.com/watch?v=41_Ne5mS2ls
– A fully assembled ribosome holds tRNA
and mRNA for use in translation.
Translation: The Process
– Translation is divided into three phases:
• Initiation
• Elongation
• Termination
Initiation
– The first phase brings together:
• The mRNA
• The first amino acid with its attached tRNA
• The two subunits of the ribosome
Elongation
– Step 1,
codon
recognition
• The
anticodon
of an
incoming
tRNA
pairs with
the mRNA
codon.
Elongation
– Step 2,
peptide
bond
formation
• The
ribosome
catalyzes
bond
formation
between
amino
acids.
Elongation
– Step 3,
translocation
• A tRNA
leaves the
P site of the
ribosome.
• The
ribosome
moves
down the
mRNA.
Termination
– Elongation continues until the ribosome
reaches a stop codon.
Review: DNA RNA Protein
– The flow of genetic information in a cell
So how do microbes
cause B cells and T cells
to grow and divide?
Each cell has a receptor on its
cell surface that recognizes a
specific part of a microbe.
That receptor triggers a
Signal transduction pathway.
This triggers gene expression
(transcription) that…
…leads to protein synthesis
(translation) that…
…allows the cell to grow
(duplicate all its proteins that
help to duplicate all its organelles)
and divide (mitosis).
On to the
Cell cycle!