PROTEIN PROTEIN SYNTHESIS SYNTHESIS
Jan 03, 2016
PROTEIN PROTEIN SYNTHESISSYNTHESIS
DNA DNA and and
GeneGeness
DNADNA
•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
Genes & ProteinsGenes & Proteins
Proteins are made of amino acids linked together by peptide bonds
20 different amino acids exist
PolypeptidesPolypeptides
•Amino acid chains are called polypeptides
DNA Begins the DNA Begins the ProcessProcess
• 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
Starting with DNAStarting with DNA• DNA DNA ‘‘s codes code must be must be copiedcopied
and taken to the cytosoland taken to the cytosol• In the cytoplasm, this In the cytoplasm, this code code
must be readmust be read so so amino amino acidsacids can be assembled to can be assembled to make polypeptides make polypeptides (proteins)(proteins)
• This process is called This process is called PROTEIN SYNTHESISPROTEIN SYNTHESIS
RNARNA
Roles of RNA and DNA
•DNA is the MASTER PLAN
•RNA is the BLUEPRINT of the
Master Plan
RNA Differs from DNARNA Differs from DNA
• RNA has a sugar RNA has a sugar riboseribose
DNA has a sugar DNA has a sugar deoxyribosedeoxyribose
Other DifferencesOther Differences
• RNA contains RNA contains the base the base uracil uracil (U(U))DNA has DNA has thymine (T)thymine (T)
• RNA molecule is RNA molecule is single-strandedsingle-strandedDNA is DNA is double-double-strandedstranded
DNA
Structure of RNAStructure of RNA
. Three Types of Three Types of RNARNA
• Messenger RNA (mRNA)Messenger RNA (mRNA) copies DNAcopies DNA’’s code & carries s code & carries the genetic information to the the genetic information to the ribosomesribosomes
• Ribosomal RNA (rRNA)Ribosomal RNA (rRNA), along , along with protein, makes up the with protein, makes up the ribosomesribosomes
• Transfer RNA (tRNA)Transfer RNA (tRNA) transfers transfers amino acids to the ribosomes amino acids to the ribosomes where proteins are where proteins are synthesizedsynthesized
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 )
Messenger RNA (mRNA)Messenger RNA (mRNA)• Carries the information for a Carries the information for a
specific proteinspecific protein• Made up of Made up of 500 to 1000 500 to 1000
nucleotides longnucleotides long• Sequence of 3 bases called Sequence of 3 bases called
codoncodon• AUGAUG – methionine or – methionine or start codonstart codon• UAA, UAG, or UGAUAA, UAG, or UGA – – stop codonsstop codons
Ribosomal RNA (rRNA)Ribosomal RNA (rRNA)
• rRNA is a single rRNA is a single strand strand 100 to 100 to 3000 nucleotides3000 nucleotides longlong
• GlobularGlobular in shape in shape• Made inside the Made inside the
nucleusnucleus of a cell of a cell• Associates with Associates with
proteins to form proteins to form ribosomesribosomes
• Site of Site of protein protein SynthesisSynthesis
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
The Genetic Code
•Use the code by reading from the center to the outside•Example: AUG codes for Methionine
Name the Amino Acids
•GGG?•UCA?•CAU?•GCA?•AAA?
Remember the Remember the Complementary Complementary
BasesBasesOn DNA: A-T C-GOn RNA: A-U C-G
Transfer RNA Transfer RNA (tRNA)(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
Transfer RNATransfer RNAamino acidamino acid
attachment siteattachment site
U A C
anticodonanticodon
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
TranscriptiTranscription and on and
TranslationTranslation
Pathway to Making a Pathway to Making a ProteinProtein
DNADNA
mRNAmRNA
tRNA (ribosomes)tRNA (ribosomes)
ProteinProtein
Protein SynthesisProtein 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
DNADNA RNARNA ProteinProtein
Nuclearmembrane
TranscriptionTranscription
RNA ProcessingRNA Processing
TranslationTranslation
DNA
Pre-mRNA
mRNA
Ribosome
Protein
EukaryotEukaryotic Cellic Cell
TranscriptionTranscription
• The process of copying the sequence of one strand of DNA, the template strand
• mRNA copies the template strand
• Requires the enzyme RNA Polymerase
Question:Question: What would be the What would be the
complementary RNA complementary RNA strand for the following strand for the following DNA sequence?DNA sequence?
DNA 5DNA 5’’--GCGTATGGCGTATG-3-3’’
Answer:Answer:
•DNA 5DNA 5’’-GCGTATG-3-GCGTATG-3’’•RNA 3RNA 3’’-CGCAUAC-5-CGCAUAC-5’’
TranscriptionTranscription
• 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
mRNA Transcript
•mRNA leaves the nucleus through its pores and goes to the ribosomes
TranslationTranslation
•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
TranscriptioTranscriptionn
TranslatiTranslationon
End Product –The End Product –The Protein!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 aa4aa5
aa200
aa199
Messenger RNA Messenger RNA (mRNA)(mRNA)
methionine glycine serine isoleucine glycine alanine stopcodon
proteinprotein
A U G G G C U C C A U C G G C G C A U A AmRNAmRNA
startcodon
Primary structure of a proteinPrimary structure of a protein
aa1 aa2 aa3 aa4 aa5 aa6
peptide bonds
codon 2 codon 3 codon 4 codon 5 codon 6 codon 7codon 1