Download RNA and Protein Synthesis

Protein Synthesis
 The production (synthesis) of
polypeptide chains (proteins)
 Two phases:
Transcription & Translation
 mRNA must be processed
before it leaves the nucleus of
eukaryotic cells
Pathway to Making a Protein
DNA
mRNA
tRNA (ribosomes)
Protein
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RNA Differs from DNA
1. RNA
DNA
2. RNA
DNA
3. RNA
DNA
has a sugar ribose
has a sugar deoxyribose
contains the base uracil (U)
has thymine (T)
molecule is single-stranded
is double-stranded
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Structure of RNA
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.
Three Types of RNA
• Messenger RNA (mRNA)
carries genetic information
to the ribosomes
• Ribosomal RNA (rRNA),
along with protein, makes
up the ribosomes
• Transfer RNA (tRNA)
transfers amino acids to
the ribosomes where
proteins are synthesized
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Messenger RNA (mRNA) carries copies of
instructions for assembling amino acids into
proteins.
Ribosomes are made up of proteins and
ribosomal RNA (rRNA).
During protein construction, transfer RNA
(tRNA) transfers each amino acid to the
ribosome.
Protein Synthesis
DNA
molecule
DNA strand
(template)
5
3
TRANSCRIPTION
mRNA
5
TRANSLATION
Protein
3
Codon
Genes & Proteins
 Proteins are made of amino
acids linked together by
peptide bonds
 20 different amino acids exist
 Amino acids chains are called
polypeptides
 Segment of DNA that codes
for the amino acid sequence in
a protein are called genes
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Two Parts of Protein Synthesis
 Transcription makes an RNA
molecule complementary to a
portion of DNA
 Translation occurs when the
sequence of bases of mRNA
DIRECTS the sequence of
amino acids in a polypeptide
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Genetic Code
 Every three bases on DNA
stands for ONE amino acid
 Each three-letter unit on
mRNA is called a codon
 Most amino acids have more
than one codon!
 The code is nearly universal
among living organisms
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Transcription
Translation
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Overview of Transcription
 During transcription in the
nucleus, a segment of DNA
unwinds and unzips, and the
DNA serves as a template
for mRNA formation
 RNA polymerase joins the
RNA nucleotides so that the
codons in mRNA are
complementary to the code in
DNA
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Transcription
DNA is copied in the
form of RNA
This first process is
called transcription.
The process begins
at a section of DNA
called a promoter.
RNA Polymerase
 Enzyme found in the
nucleus
 Separates the two DNA
strands by breaking the
hydrogen bonds between
the bases
 Then moves along one of
the DNA strands and links
RNA nucleotides together
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RNA
Messenger RNA (mRNA)
• Carries the information for a
specific protein
• Made up of 500 to 1000
nucleotides long
• Sequence of 3 bases called
codon
• AUG – methionine or start codon
• UAA, UAG, or UGA – stop
codons
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A codon consists of three
consecutive nucleotides on mRNA
that specify a particular amino acid.
Messenger RNA (mRNA)
start
codon
mRNA
A
U
G
codon 1
G
G
C
codon 2
protein methionine
glycine
U
C
codon 3
serine
C
A
U
C
codon 4
isoleucine
G
G
C
codon 5
glycine
G
C
A
codon 6
U
A
codon 7
stop
codon
alanine
Primary structure of a protein
aa1
aa2
aa3
aa4
aa5
aa6
peptide bonds
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A
The Genetic Code
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Transfer RNA (tRNA)
• Picks up the appropriate amino
acid floating in the cytoplasm
• Transports amino acids to the
mRNA
• Have anticodons that are
complementary to mRNA codons
• Recognizes the appropriate
codons on the mRNA and bonds
to them with H-bonds
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Translation
• Synthesis of proteins in
the cytoplasm
• Involves the following:
1. mRNA (codons)
2. tRNA (anticodons)
3. ribosomes
4. amino acids
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Translation
Translation is the decoding of an mRNA
message into a polypeptide chain (protein).
Translation takes place on ribosomes.
During translation, the cell uses information
from messenger RNA to produce proteins.
Nucleus
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mRNA
The ribosome binds new tRNA
molecules and amino acids as it moves
along the mRNA.
Phenylalanine
Methionine
Ribosome
mRNA
Start codon
tRNA
Lysine
Protein Synthesis
Translation
The process continues until the ribosome reaches a
stop codon.
Polypeptide
Ribosome
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gkPEAo