Download What is a protein

Protein Synthesis
The making of proteins
Why Do We Need Proteins?
Why Do We Need Proteins?
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Cell structure – Cellular
material is 80% composed of
proteins
Cellular processes –
hormones and enzymes
Membrane channel proteins
for transport of materials in
and out of the cells
Cell identification
To initiate responses.
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Neurotransmitters
Antibodies
Clotting blood
Pigments
etc...
What is a protein ?
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One of the bodies most abundant organic molecules
Made up of 20 kinds of amino acids
100`s of these amino acids are linked together in chains
to make one protein molecule (polypeptide).
The sequence of the particular amino acids determines
its shape.
The shape of the protein determines
its particular function.
What do we need for protein synthesis?
1. DNA – the template for making mRNA through
transcription.
2. RNA – there are three kinds
a) mRNA – messenger RNA. Makes and takes a
copy of the DNA to the cytoplasm where protein
is constructed.
b) tRNA – transfer RNA. The compliment to
mRNA. Collects the amino acids and brings
them to the ribosomes where polypeptide chains
are assembled according to the sequence on the
mRNA
c) rRNA – ribosomal RNA. Part of the
ribosome, reads the mRNA and directs the tRNA
What do we need for
protein synthesis?
3. Amino Acids – building
blocks of protein
4. Ribosomes - reads the
mRNA, directs the tRNA
and creates protiens by
binding the amino acids
together through
translation.
Each in more detail - DNA
Contains the information to make all the proteins
in our body.
Problem: Protein is not made in the nucleus.
DNA is too big to leave the nucleus.
How do we get the information from the DNA
out of the nucleus to where the protein is made?
Each in more detail - RNA
RNA: ribonucleic acid.
 Smaller than DNA
 Function: Helps us get DNA information out of the nucleus. Made in
the nucleus but found mostly in the cytoplasm.
RNA is used to directly make protein.
 Consists of a) single strand of nucleotides
b) ribose as the sugar chain
c) a phosphate group
d) four base pairs (one different from DNA.)
Adenine, guanine, cytocine and Uracil
 Uracil is a pyrimidine base that replaces thymine and bonds with adenine
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C-G and A-U
RNA Differs from DNA
1. RNA is smaller
2. RNA has a sugar ribose
DNA has a sugar deoxyribose
3. RNA contains the base uracil (U)
DNA has thymine (T)
4. RNA molecule is single-stranded
DNA is double-stranded
Structure of RNA
Each in more detail - Amino Acids
Long chains of amino acids link together to make a
polypeptide chain (protein)
Every amino acid has 5 parts
1.
Central carbon
2.
Amino group
3.
Carboxyl Acid group
4.
A single hydrogen
5.
The ``R`` group – a chain that varies making each of the
20 amino acids unique
It is the sequence of nucleic acids on the mRNA strand that
determines which amino acids go together.
Let’s Review the Steps we Know
so Far…
1. DNA makes a message (DNA makes mRNA)
2. Message is sent out into the cytoplasm (mRNA leaves
the nucleus)
3. Message arrives at destination (mRNA goes to
ribosome).
4. Message is read and directions followed (tRNA reads
the mRNA, a small piece at a time, and gets whatever
amino acid that small piece of mRNA says to get).
5. A protein is assembled
Steps of Protein Synthesis
Transcription (writing the “message”)
Using DNA to make mRNA which is the
messenger that carries code to cytoplasm
Translation (reading the “message”)
mRNA and tRNA assemble the amino acid
chain. In other words the message is translated
into a protein.
Transcription
Transcription is the process of copying a sequence
of DNA to produce a complementary strand of
RNA.
Occurs in the nucleus.
Only one gene is transferred into a message, not
the entire chromosome.
Transcription – The making of RNA
RNA polymerase and other proteins form a
transcription complex.
The transcription complex recognizes the start
of a gene and unwinds a segment of it.
start site
transcription complex
nucleotides
Transcription – The making of RNA
Nucleotides pair with one strand of the DNA.
RNA polymerase bonds the nucleotides
together.
The DNA helix winds again as the gene is
transcribed.
DNA
Transcription – The making of RNA
The RNA strand detaches from the DNA once
the gene is transcribed.
The DNA zips back up and the single strand of
RNA is released.
RNA
Transcription is similar to Replication
Transcription and replication both involve complex
enzymes and complementary base pairing.
The two processes have different end results.
Replication copies all the DNA;
Transcription copies a segment of
the DNA – one gene.
 Replication makes one copy;
Transcription can make many copies.
 In replication the pairs stay together
In transcription the copied RNA strand breaks away
and the two strands of DNA rebind and recoil.
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Transcription
Summing Transcription up in
simple terms
1. DNA unzips.
2. RNA bases attach to make strand of mRNA
COMPLEMENTARY to DNA (just like when
we copied DNA)
3. Only one strand is made (like open-faced
sandwich).
4. Use URACIL instead of thymine.
5. mRNA leaves nucleus
6. DNA zips back up.
Translation – The making of a protein
Amino acids are coded by mRNA base sequences.
Translation converts mRNA messages into
polypeptides.
A codon is a sequence of three nucleotides that
codes for an amino acid.
codon for
methionine (Met)
codon for
leucine (Leu)
Translation – The making of a protein
The mRNA joins with the ribosome which begins
reading the code of nucleic acids
Any portion of the strand NOT responsible for
coding a polypeptide is discarded and is called
INTRON
The nucleotide sequence that encodes the amino
acid sequence (called EXON) is identified by
the AUG initiator codon and later followed by a
terminator.
Translation – The making of a protein
Each codon matches a specific amino acid or
function. ***Use the codon to read the chart***
Twenty possible
amino acids
 three stop codons
 one start codon,
codes for the amino
acid methionine
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Translation – The making of a protein
A change in the order in which codons are read
changes the resulting protein.
Regardless of the organism, codons code for the
same amino acid.
Translation – The making of a protein
This is a molecule of messenger RNA.
It was made in the nucleus by transcription
from a DNA molecule.
Each set of three nucleotides is a codon.
Initiator codon
another
codon
A U G G G C U U AAA G C A G U G C A C G U U
mRNA molecule
Translation – The making of a protein
A ribosome either free in the cytoplasm or
attached to the rough endoplasmic
reticulum connects to the mRNA molecule.
ribosome
A U G G G C U U AAA G C A G U G C A C G U U
Translation – The making of a protein
Amino acid
Met
tRNA molecule
anticodon
A transfer RNA molecule arrives.
It brings an amino acid to the first
three bases (codon) on the mRNA.
The three unpaired bases (anticodon)
on the tRNA link up with the codon.
UAC
A U G G G C U U AAA G C A G U G C A C G U U
Translation – The making of a protein
Met
Another tRNA molecule comes
into place, bringing a second
amino acid.
Its anticodon links up with the
second codon on the mRNA.
UAC
A U G G G C U U AAA G C A G U G C A C G U U
Translation – The making of a protein
Met
Gly
Peptide bond
A peptide bond forms between
the two amino acids.
A U G G G C U U AAA G C A G U G C A C G U U
Translation – The making of a protein
Met
Gly
The first tRNA molecule
releases its amino acid and
moves off into the cytoplasm.
A U G G G C U U AAA G C A G U G C A C G U U
Translation – The making of a protein
Met
Gly
The ribosome moves along the
mRNA to the next codon.
A U G G G C U U AAA G C A G U G C A C G U U
Translation – The making of a protein
Met
Gly
Another tRNA molecule
brings the next amino
acid into place.
A U G G G C U U AAA G C A G U G C A C G U U
Translation – The making of a protein
Met
Gly
Leu
A peptide bond joins the
second and third amino acids
to form a polypeptide chain.
A U G G G C U U AAA G C A G U G C A C G U U
Translation – The making of a protein
Met
Gly
Leu
Lys
Glu
The process continues.
The polypeptide chain gets
longer.
This continues until a
terrmination (stop) codon is
reached.
The polypeptide is complete.
A U G G G C U U AAA G C A G U G C A C G U U
Summing Translation up in
simpler terms
1.
2.
3.
4.
mRNA goes to ribosome in cytoplasm (proteins made here!)
Exon is identified by the START codon (AUG)
Intron is discarded
tRNA reads each codon (three nucleotide set code for
amino acid) and transfers the correct amino acid accordingly.
5. The amino acids are linked together in the codon order.
6. tRNA will read the mRNA until it reaches a TERMINATOR
or STOP codon at which point the polypeptide is released
from the ribosome.
7. This string of amino acids takes on it’s unique shape PROTEIN!
Synthesis Practice
DNA
triplet
TAC
CCT
GGA
ACC
TAT
ACT
mRNA
codon
tRNA
Anticodon
Amino
Acid
Synthesis Practice
DNA
triplet
TAC
CCT
GGA
ACC
TAT
ACT
mRNA
codon
AUG
tRNA
Anticodon
Amino
Acid
Synthesis Practice
DNA
triplet
TAC
CCT
GGA
ACC
TAT
ACT
mRNA
codon
AUG
tRNA
Anticodon
UAC
Amino
Acid
Synthesis Practice
DNA
triplet
TAC
CCT
GGA
ACC
TAT
ACT
mRNA
codon
AUG
tRNA
Anticodon
UAC
Amino
Acid
MET
Synthesis Practice
DNA
triplet
TAC
mRNA
codon
AUG
CCT
GGA
GGA
ACC
TAT
ACT
tRNA
Anticodon
UAC
Amino
Acid
MET
Synthesis Practice
DNA
triplet
TAC
mRNA
codon
AUG
tRNA
Anticodon
UAC
CCT
GGA
CCU
GGA
ACC
TAT
ACT
Amino
Acid
MET
Synthesis Practice
DNA
triplet
TAC
mRNA
codon
AUG
tRNA
Anticodon
UAC
Amino
Acid
MET
CCT
GGA
CCU
GLY
GGA
ACC
TAT
ACT
Synthesis Practice
DNA
triplet
TAC
mRNA
codon
AUG
tRNA
Anticodon
UAC
Amino
Acid
MET
CCT
GGA
CCU
GLY
GGA
CCU
ACC
TAT
ACT
Synthesis Practice
DNA
triplet
TAC
mRNA
codon
AUG
tRNA
Anticodon
UAC
Amino
Acid
MET
CCT
GGA
CCU
GLY
GGA
CCU
GGA
ACC
TAT
ACT
Synthesis Practice
DNA
triplet
TAC
mRNA
codon
AUG
tRNA
Anticodon
UAC
Amino
Acid
MET
CCT
GGA
CCU
GLY
GGA
CCU
GGA
PRO
ACC
TAT
ACT
Synthesis Practice
DNA
triplet
TAC
mRNA
codon
AUG
tRNA
Anticodon
UAC
Amino
Acid
MET
CCT
GGA
CCU
GLY
GGA
CCU
GGA
PRO
ACC
UGG
ACC
TRP
TAT
ACT
Synthesis Practice
DNA
triplet
TAC
mRNA
codon
AUG
tRNA
Anticodon
UAC
Amino
Acid
MET
CCT
GGA
CCU
GLY
GGA
CCU
GGA
PRO
ACC
UGG
ACC
TRP
TAT
AUA
UAU
ILE
ACT
Synthesis Practice
DNA
triplet
TAC
mRNA
codon
AUG
tRNA
Anticodon
UAC
Amino
Acid
MET
CCT
GGA
CCU
GLY
GGA
CCU
GGA
PRO
ACC
UGG
ACC
TRP
TAT
AUA
UAU
ILE
ACT
UGA
Termination
Over simplified Protein synthesis
1. DNA unzips
2. mRNA made from DNA.
3. mRNA leaves nucleus and enters ribosome.
4. tRNA reads mRNA from “start” to “stop”
5. As tRNA reads mRNA, it brings the correct
amino acids.
6. Amino acids are linked together to make a protein
DNA makes mRNA (complement)
mRNA matches up with tRNA (complement)
tRNA brings amino acid
Sources
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library.thinkquest.org/.../cell_membrane.gif
www.viewingspace.com/.../genetic_code.gif
www.etsu.edu/.../amino_acid_structure_4.jpg
www.northallertoncoll.org.uk/biology/Protein%20Synthesis.ppt
http://coral.nutleyschools.org/~jmowrey/biolivingnotes/protein/Protein%2
0Synthesis%20Lesson.pdf
http://biology-1cp.hanna.anderson5.net/modules/groups/integrated_home.phtml?gid=40155
&sessionid=0e0ead763c304672d5ac0ddf7fa2b5c3
www.scientificpsychic.com/.../aminoacids1.html