Transcript Protein Synthesis

Protein Synthesis
Review for Keystone
Help! I broke a nail!
• What are nails made of?
– A protein called keratin
• How does your body make a new nail to
replace the one that broke off?
– The body needs to make more keratin
(Keratin is a protein. Remember: If it ends in
“in” it is a protein)
• In order to make anything what 2 things are
necessary?
– Instructions
– Materials
In our bodies the making of new protein (like
keratin) is called protein synthesis
• What serves as the instructions?
DNA in the cell
• Where do you think the building materials
come from?
from food! (protein that you eat is
broken down into amino acids, the amino acids
are then used to build the needed protein)
So HOW does it work?
• Your body makes proteins in 2 Parts:
1. Reads, Copies, Edits the Instructions (Transcription)
2. Assembles the protein using amino acids and following
the transcript instructions (Translation)
• To make new keratin to form a new fingernail first
you need the instructions
• Somewhere in the DNA is one region that provides
the instructions for making keratin.
What do you call a region of DNA like this that “codes”
for something?
-a gene!
Part 1: TRANSCRIPTION
Reading, Copying, Editing the
Gene
• Where is this happening? Do you remember
where DNA is located?
– In the nucleus, in the form of chromosomes
• Let’s pretend that this is the gene for keratin:
A closer look:
REMEMBER: The DNA
code is made up of
nucleotides, A, T, C and G
A pairs with T
C pairs with G
A T G T G G
T
A G T C A C G G G T G A
A C A C C T C A G T G C C C A C T
Only one side of the DNA strand is
“read”. This side is called the
template strand. Let’s say its this one
• Here is the tricky part. DNA cannot leave the
nucleus. We need to make a complimentary
copy of the gene and carry the copy out of the
nucleus.
RNA POLYMERASE locates the
• An enzyme called _______________
gene among all of the DNA, opens up the
strand and produces a “transcript”, a
complimentary strand of the DNA template
• The transcript is actually made of RNA. It is
called an mRNA
Now you make the transcript:
• Remember: The transcript is not an identical
copy but a complimentary strand. If C is
read, G is added to the growing transcript.
• Remember: Use U instead of T for RNA
• Your mRNA transcript should look like this:
A U G U G G A G U C A C G G G U G A
Before this mRNA leaves the nucleus it is edited. Certain
parts of the code are cut out.
introns
The portions removed are called _____________.
The portions that remain are called ____________.
exons
Lets say UGG and AGU are introns.
What would the final mRNA look like?
Final mRNA:
A U G C A C
G G G U G A
TRANSCRIPTION IS OVER!
All of this was happening in the nucleus. Now
the final mRNA transcript leaves the nucleus
and arrives at a ribosome in the cytoplasm for
translation.
Part 2: TRANSLATION
Reading the transcript and assembling the correct
amino acids into the protein needed
• Look at your final mRNA transcript. The code is
read 3 nucleotides at a time. This is called a codon.
Each codon corresponds to 1 amino acid.
• tRNAs carry over the correct amino acid and attach
them together (form peptide bonds between
them)
• How do you know which amino acids will come
together to make the protein?
Use the genetic code!
The Genetic Code
What amino acids do you get for
the codons in this mRNA?
AUG=
CAC=
GGG=
UGA=
METHIONINE
HISTIDINE
GLYCINE
STOP
METHIONINE-HISTIDINE-GLYCINE = KERATIN (JUST AS AN
EXAMPLE. The actual protein
is much longer)
REVIEW
TRANSCRIPTION
• Starts with a gene for a
particular protein
• Happens in the nucleus
• RNA polymerase does
all the work
• The final product is an
mRNA transcript
TRANSLATION
• Starts with the mRNA
transcript
• Happens at a ribosome
• tRNAs do all the work
• The final product is a
strand of amino acids
that fold into the
protein!
What if the code is changed?
Any change in the DNA code is called a
mutation.
Sometimes the change still codes for the same
amino acid and forms the same protein so
there is no noticeable effect.
Other times the change results in the wrong
amino acid. The necessary protein will not
form. This could result in a disorder of some
kind.
From the pretest…
1. Which of the following is arranged from largest to smallest?
A.
B.
C.
D.
chromosome, nucleus, gene
gene, nucleus, chromosome
nucleus, chromosome, gene
chromosome, gene, nucleus
C. Nucleus, chromosome, gene
2. The pathway, DNA mRNA 
ribosome  tRNA  protein, taken by
the genetic code during protein synthesis
happens in
B. ALL organisms
A.eukaryotes only.
B.all organisms.
C.prokaryotes only.
D.no organisms.
(prokaryotes do not have
a nucleus but they have
ribosomes)
THIS IS THE
CENTRAL
DOGMA OF
BIOLOGY!
(CORE CONCEPT)
B. Assembling a
protein.
This is a ribosome
3.
Structure 1 aids in the process of protein synthesis by
A. providing the code for assembling a protein.
B. assembling a protein.
C. providing the energy needed for protein synthesis.
D. allowing the movement of substances into the cell for
the process of protein synthesis.
Use the chart to help you answer number 25.
Codon
UUU
UCA
CAA
GCG
CAG
AUA
Amino Acid
Phenylalanine
Serine
Glutamine
Alanine
Histidine
Isoleucine
Codon
AUC
GUC
AAU
GAC
CCG
CUA
C. AUA and AUC both code
for the same amino acid,
isoleucine
Amino Acid
Isoleucine
Valine
Asparagine
Aspartic acid
Proline
Leucine
1. Diabetes is a disease characterized by the inability to break down sugars. Often
a person with diabetes has a defective DNA sequence that codes for the making
of insulin protein. Suppose a person has a mutation in his/her DNA and the first
triplet for the insulin gene reads T A T instead of T A G which is the normal
gene for insulin. Will the person with this mutation be diabetic?
A. Yes, because any mutation will cause disease.
B. Yes, because the insulin protein will be changed.
C. No, because the insulin protein is still produced.
D. No, because it is a gene mutation and not a chromosomal mutation.