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PROTEIN SYNTHESIS
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DNA and Genes
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DNA
DNA contains genes, sequences of nucleotide bases
These Genes code for polypeptides (proteins)
Proteins are used to build cells and do much of the work inside cells
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Genes & Proteins
Proteins are made of amino acids linked together by peptide bonds
20 different amino acids exist
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Amino Acid Structure
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Polypeptides
Amino acid chains are called polypeptides
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DNA Begins the Process
DNA is found inside the nucleus
Proteins, however, are made in the cytoplasm of cells by organelles called ribosomes
Ribosomes may be free in the cytosol or attached to the surface of rough ER
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Starting with DNA
DNA ‘s code must be copied and taken to the cytosol
In the cytoplasm, this code must be read so amino acids can be assembled to make polypeptides (proteins)
This process is called PROTEIN SYNTHESIS
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RNA
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10. RNA is the BLUEPRINT of the Master Plan
Roles of RNA and DNA
DNA is the MASTER PLAN
RNA is the BLUEPRINT of the Master Plan
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RNA Differs from DNA
RNA has a sugar ribose
DNA has a sugar deoxyribose
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Other Differences
RNA contains the base uracil (U)
DNA has thymine (T)
RNA molecule is single-stranded
DNA is double-stranded
DNA
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Structure of RNA
Like DNA, RNA is a polymer of nucleotides. In an RNA nucleotide, the sugar ribose is attached to a phosphate molecule and to a base, either G, U, A, or C. Notice that in RNA, the base uracil replaces thymine as one of the pyrimidine bases. RNA is single-stranded, whereas DNA is double-stranded.
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Three Types of RNA
Messenger RNA (mRNA) copies DNA’s code & carries the 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
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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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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Ribosomal RNA (rRNA)
rRNA is a single strand 100 to 3000 nucleotides long
Globular in shape
Made inside the nucleus of a cell
Associates with proteins to form ribosomes
Site of protein Synthesis
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The Genetic Code
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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21. Remember the Complementary Bases
On DNA:
A-T
C-G
On RNA:
A-U
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Transfer RNA (tRNA)
Clover-leaf shape
Single stranded molecule with attachment site at one end for an amino acid
Opposite end has three nucleotide bases called the anticodon
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Transfer RNA
amino acid
attachment site 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
Example: Codon ACU
Anticodon UGA
UGA
ACU
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25. Transcription and Translation
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26. Pathway to Making a Protein
DNA
mRNA
tRNA (ribosomes)
Protein
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Protein Synthesis
The production or synthesis of polypeptide chains (proteins)
Two phases: Transcription & Translation
mRNA must be processed before it leaves the nucleus of eukaryotic cells
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DNA  RNA  Protein
Nuclear
membrane
Transcription
RNA Processing
Translation
DNA
Pre-mRNA
mRNA
Ribosome
Protein
Eukaryotic Cell
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Transcription
The process of copying the sequence of one strand of DNA, the template strand
mRNA copies the template strand
Requires the enzyme RNA Polymerase
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Template Strand
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Question:
What would be the complementary RNA strand for the following DNA sequence?
DNA 5’-GCGTATG-3’
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Answer:
DNA 5’-GCGTATG-3’
RNA 3’-CGCAUAC-5’
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Transcription
During transcription, RNA polymerase binds to DNA and separates the DNA strands
RNA Polymerase then uses one strand of DNA as a template to assemble nucleotides into RNA
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Transcription
Promoters are regions on DNA that show where RNA Polymerase must bind to begin the Transcription of RNA
Called the TATA box
Specific base sequences act as signals to stop
Called the termination signal
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RNA Polymerase
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mRNA Transcript
mRNA leaves the nucleus through its pores and goes to the ribosomes
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Translation
Translation is the process of decoding the mRNA into a polypeptide chain
Ribosomes read mRNA three bases or 1 codon at a time and construct the proteins
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Transcription
Transcription occurs when DNA acts as a template for mRNA synthesis. Translation occurs when the sequence of the mRNA codons determines the sequence of amino acids in a protein.
Translation
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Ribosomes
Made of a large and small subunit
Composed of rRNA (40%) and proteins (60%)
Have two sites for tRNA attachment
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40. End Product –The Protein!
The end products of protein synthesis is a primary structure of a protein
A sequence of amino acid bonded together by peptide bonds
aa1
aa2
aa3
aa4
aa5
aa200
aa199
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Messenger RNA (mRNA) A U G C
mRNA
start
codon
codon 2
codon 3
codon 4
codon 5
codon 6
codon 7
codon 1
methionine
glycine
serine
isoleucine
alanine
stop
codon
protein
Primary structure of a protein
aa1
aa2
aa3
aa4
aa5
aa6
peptide bonds
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