Transcript From Genes to Proteins

From Genes to Proteins
All About RNA
Quick Review
• The building blocks of proteins are amino
acids.
• They have many different functions. They
can be enzymes, hormones, or any of a
number of substances your body needs.
• Ribosomes are the site of protein
synthesis.
• RNA is made of nucleotides.
– A phosphate group
– Ribose
– Nitrogen base
• RNA is a single strand.
• RNA uses uracil instead of thymine.
• Three types:
– mRNA – messenger RNA
– tRNA – transfer RNA
– rRNA – ribosomal RNA
The instructions for making a protein are
encoded in the genes in the DNA.
The instructions for making the protein are
transferred from a gene to an mRNA
molecule in a process called
transcription.
• Cells then use tRNA and rRNA to read the
instructions on the mRNA molecule and put
together the amino acids that make up the
protein in a process called translation.
Transcription
• Takes place in the nucleus.
• Starts at a ‘start’ signal and ends with a
‘stop’ signal.
• Requires RNA polymerase
– Opens DNA
– Adds complementary nucleotides of RNA
•mRNA then leaves through the nuclear pores out
to the cytoplasm where it settles on a ribosome.
Genetic Code
• The instructions for making proteins are
written as a series of three-nucleotide
sequences on the mRNA called codons.
• Each codon codes for an amino acid or
signals a start or stop for translation.
• AUG = start
• UAG = stop
UAG (STOP)
• Do the Quick Lab on page 210…
Translation
• Takes place in the cytoplasm on the
ribosomes.
• tRNA molecules are single strands of RNA
that temporarily carry an amino acid on
one end.
• Each tRNA contains an anticodon for the
mRNA’s codon.
• The anticodon is a three-nucleotide
sequence that is complementary to a
particular mRNA codon.
Translation continues…
• When a tRNA’s anticodon matches up with
the codon of mRNA, it drops off its’ amino
acid.
• Each amino acid forms a peptide bond
with the previous amino acid which results
in the production of a protein.
DATA LAB
Keratin is one of the proteins in hair. The
gene for keratin is transcribed and
translated by certain skin cells. The series
of letters on the next slide represents the
sequence of nucleotides in a portion of an
mRNA molecule transcribed from the gene
for keratin. This mRNA strand and the
genetic code on page 211 can be used to
determine some of the amino acids in
keratin.
UCUCGUGAAUUUUCC
1. Determine the sequence of amino acids that
will result from the translation of the segment
of mRNA above. (Use chart on p. 211.)
2. Determine the anticodon of each tRNA
molecule that will bind to this mRNA segment.
3. Determine the sequence of nucleotides in the
segment of DNA from which the mRNA strand
above was transcribed.
4. Determine the sequence of nucleotides in the
segment of DNA that is complementary to the
DNA segment described in item 3.
Environmental Factors and
Protein Synthesis
The development of a growing
zygote (fertilized egg) is
controlled by different types
of proteins produced by that
cell. Certain factors can
inhibit, enhance, or change
the way those proteins work.
http://www.idreamofzygotes.com/.a/6a01287709b095970c0128
77135951970c-800wi
For instance…
Temperature
Temperature can
affect the sex of
some reptiles.
This graph shows
that for different
reptiles the
number of males
vs. females that
are born at
different
temperatures.
So…temperature determines the synthesis of
the proteins that are responsible for telling the
cells to produce males or females. Makes you
want to watch Jurassic Park!
Water
Some species of
animals, including
frogs and insects that
lay eggs in ponds that
evaporate quickly,
have developed an
adaptation that allows
metamorphosis to
occur more quickly.
So…the availability of water determines the
synthesis of the proteins that are responsible
for telling the cells to develop more quickly.
Frogs: yea! Mosquitoes? Not so much…
Nutrients
Lack of certain
proteins, fats,
carbohydrates,
minerals, or vitamins
can cause cells to
produce incorrect
proteins or to not
produce certain
proteins, at all. This
can lead to many
So…the availability of nutrients determines
disorders.
which proteins are synthesized. Salad, anyone?
Just checking!
1. How many types of RNA are there and
what are they?
2. What are the two steps to protein
synthesis?
3. Discuss how protein synthesis is
necessary to development in all
organisms, no matter how small.