Protein Synthesis Overview

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Transcript Protein Synthesis Overview

Bell Ringer
Compare and Contrast:
DNA and RNA
Bell Ringer
• What organelle is responsible for
protein synthesis (making
proteins)?
• What types of cells have this
organelle?
• Where in the cell can this
organelle be found?
Bell Ringer (1)
•What are the 3 types
of RNA?
•What is the function
of each type?
Protein Synthesis:
An Overview
Day 5 Unit 5
Goal: Students will be able to describe the
processes of transcription and translation.
Protein Synthesis Foldable
Transcription
Translation
1. Where?
2. What molecules
are involved?
3. What is
produced?
4. Where does it go?
5. What happens?
1. Where?
2. What molecules
are involved?
3. What is
produced?
4. Where does it go?
5. What happens?
Back of Foldable
• Central Dogma
• Amino Acids &
Nucleotides
• Codons
• Types of RNA
– Start =
– Stop =
Structure of RNA
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Pathway to Making a
Protein
DNA
mRNA
tRNA (ribosomes)
Protein
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DNA  RNA  Protein
Nuclear
membrane
DNA
Transcription
Eukaryotic
Cell
Pre-mRNA
RNA Processing
mRNA
Ribosome
Translation
Protein
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Types of RNA
• Messenger RNA (mRNA) makes a copy of
DNA
• Transfer RNA (tRNA) decodes mRNA and
transfers amino acids to the ribosome
• Ribosomal RNA (rRNA) build the protein
by bonding amino acids together.
Ribosomes are made of rRNA.
Protein Synthesis
• Protein synthesis uses the
information in genes to make
proteins.
• 2 Steps
–Transcription
–Translation
Transcription: Where?
• mRNA is made in the NUCLEUS
• mRNA will leave the nucleus through the
pores in the nuclear membrane
• (DNA does NOT leave the nucleus)
Transcription: Involved Molecules
• DNA (instructions for making the protein)
• mRNA (copy of the instructions)
• RNA polymerase (enzyme that builds
mRNA)
RNA Polymerase =
The Enzyme responsible for Transcription
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Transcription: Produces?
• mRNA (messenger
RNA)
• Long Straight chain
of Nucleotides
• Made in the Nucleus
• Copies DNA & leaves
through nuclear
pores
• Contains the
Nitrogen Bases A, G,
C, U ( no T )
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Remember the
Complementary Bases
On DNA:
A-T
C-G
On RNA:
A-U
C-G
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Transcription: What Happens?
Big Idea: DNA is copied into a
complementary sequence of mRNA.
RNA polymerase is the enzyme that is
responsible for transcription
DNA = GCCATT
mRNA = CGGUAA
Adenine (DNA and RNA)
Cystosine (DNA and RNA)
Guanine(DNA and RNA)
Thymine (DNA only)
Uracil (RNA only)
RNA
polymerase
DNA
RNA
Transcription: Goes to?
•mRNA leaves the nucleus through the
pores in the nuclear membrane and
goes to the cytoplasm & ribosomes
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The Genetic Code
• Each gene on a strand of DNA is read
in 3 base sequences called codons
• A codon designates an amino acid
• An amino acid may have more than
one codon
• There are 20 amino acids, but 64
possible codons
• Some codons tell the ribosome to stop
translating
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The Genetic Code
•Use the
code by
reading from
the center to
the outside
•Example:
AUG codes
for
Methionine
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Name the Amino Acids
•
•
•
•
•
GGG?
UCA?
CAU?
GCA?
AAA?
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Start/Stop Codons
• There will always be a “Start” codon
(AUG) at the beginning. It is like
capitalizing the 1st letter of a sentence.
• There will always be a “Stop” codon
(UGA, UAA, UAG) at the end. It is like a
period at the end of a sentence.
Translation
Translation: Where?
• Ribosome
–Free floating ribosome in cytoplasm
(makes proteins for that cell)
OR
–attached ribosome on the Rough
ER (makes proteins to be exported
to other cells)
Translation: Involved Molecules
• mRNA (copy of the instructions)
• tRNA (translates the instructions)
• rRNA (builds the protein)
Transfer RNA
amino acid
attachment site
• Decodes (translates)
the mRNA
• Transfers amino
acids to the
ribosome
U A C
anticodon
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Codons and Anticodons
• The 3 bases of an
anticodon are
complementary to
the 3 bases of a
codon
• Ex: Anticodon UGA
•
Codon ACU
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UGA
ACU
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Ribosomal RNA (rRNA)
• rRNA is a single strand
100 to 3000 nucleotides
long
• Globular in shape
• Made inside the nucleus
(nucleolus) of a cell
• Associates with proteins to
form ribosomes
• Site of protein Synthesis
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Translation: Produces?
• Chain of
amino acids
• Polypeptide
(protein)
Translation: What Happens?
1. tRNA translates the mRNA using
“anticodons.” (complementary to the codon)
– Each tRNA molecule has an anticodon on
one end and an amino acid on the other.
2. tRNA transfers the amino acids to the
ribosome in the correct sequence.
3. rRNA forms peptide bonds between
the amino acids. This links them
together to build the protein.
Translation: Where does it go?
The protein will do one of 2 things
• Stay inside the cell to carry out functions
for that cell
OR
• Be exported to other cells
– Rough ER  Golgi  Exocytosis
Nucleus
Messenger RNA
Messenger RNA is transcribed in the nucleus.
Phenylalanine
tRNA
mRNA
Transfer RNA
Methionine
The mRNA then enters the cytoplasm and attaches
to a ribosome. Translation begins at AUG, the start
codon. Each transfer RNA has an anticodon
whose bases are complementary to a codon on the
mRNA strand. The ribosome positions the start
codon to attract its anticodon, which is part of the
tRNA that binds methionine. The ribosome also
binds the next codon and its anticodon.
Ribosome
mRNA
Lysine
Start codon
The Polypeptide “Assembly Line”
The ribosome joins the two amino acids—
methionine and phenylalanine—and breaks the
bond between methionine and its tRNA. The
tRNA floats away, allowing the ribosome to bind
to another tRNA. The ribosome moves along
the mRNA, binding new tRNA molecules and
amino acids.
Lysine
Growing polypeptide chain
Ribosome
tRNA
tRNA
mRNA
Completing the Polypeptide
mRNA
Translation direction
Ribosome
The process continues until the ribosome reaches
one of the three stop codons. The result is a growing
polypeptide chain.
Mutations
• Gene Mutations — result from
a change in a single gene
• Chromosomal Mutations —
the whole chromosome is
changed
Gene Mutations: result from a
change in a single gene
• Point Mutations = affect 1 nucleotide;
switches one nucleotide for another
– This only affects 1 amino acid in the protein
sequence
– May also be called Substitution
• Example
– THE CAT ATE THE RAT (normal)
– THE CAT ARE THE RAT (mutation)
Gene Mutations: result from a
change in a single gene
• Frameshift mutations affect how the entire
gene is read.
– Insertion or Deletion—a nucleotide is inserted or
deleted from the sequence
– This changes the codons FROM THAT POINT ON!
All the remaining amino acids will be affected.
• Example
– THE ACA TAT ETH ERA T. (insertion mutation)
– THE CAT ATE THE RAT. (normal)
– THC ATA TET HER AT. (deletion mutation)
Protein Synthesis Activity
• Step 1: Transcription
– Copy the “gene” into the complementary
sequence of mRNA.
– This must be done in the “Nucleus.”
• Step 2: Translation
– Translate the mRNA using the “tRNA cards”
posted around the room. The codon should
match up with a word.
– If you have done this correctly, your sentence
should make sense!!!
– Don’t forget the punctuation (Start/Stop codons)!!
QOD (1)
•What happens during
transcription?
•What happens during
translation?