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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
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AMINO ACID STRUCTUREAMINO ACID STRUCTURE
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POLYPEPTIDESPOLYPEPTIDES
Amino acid chains are called polypeptides
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DNA BEGINS THE DNA BEGINS THE PROCESSPROCESS
DNA is found inside the nucleus Proteins, however, are made in the
cytosol 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 DNASTARTING WITH DNA DNA ‘s codeDNA ‘s code must be must be copiedcopied
and taken to the cytosoland taken to the cytosol In the cytosol, this In the cytosol, this code code
must be readmust be read so so amino acidsamino acids can be assembled to make can be assembled to make polypeptides (proteins)polypeptides (proteins)
This process is called This process is called PROTEIN SYNTHESISPROTEIN SYNTHESIS
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RNARNA
DNA is the MASTER PLAN
RNA is the BLUEPRINT of the
Master Plan
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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
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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
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DNA
STRUCTURE OF RNASTRUCTURE OF RNA
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THREE TYPES OF RNATHREE TYPES OF RNA Messenger RNA (mRNA)Messenger RNA (mRNA)
copies DNA’s code & carries copies DNA’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
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.
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)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
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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
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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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•Use the code by reading from the center to the outside•Example: AUG codes for Methionine
GGG? UCA? CAU? GCA? AAA?
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REMEMBER THE COMPLEMENTARY BASESREMEMBER THE COMPLEMENTARY BASES
On DNA: A-T C-GOn RNA: A-U C-G
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TRANSFER RNA (TRNA)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 RNATRANSFER RNA
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amino acidamino acidattachment siteattachment site
U A C
anticodonanticodon
The 3 bases of an anticodon are complementary to the 3 bases of a codon
Example: Codon ACU
Anticodon UGA
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UGA
ACU
TRANSCRIPTION TRANSCRIPTION AND TRANSLATIONAND TRANSLATION
PATHWAY TO MAKING A PROTEINPATHWAY TO MAKING A PROTEIN
DNADNA
mRNAmRNA
tRNA (ribosomes)tRNA (ribosomes)
ProteinProtein26
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
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DNADNA RNARNA PROTEINPROTEIN
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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
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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 5’-DNA 5’-GCGTATGGCGTATG-3’-3’
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ANSWER:ANSWER:
DNA 5’-GCGTATG-DNA 5’-GCGTATG-3’3’
RNA 3’-CGCAUAC-RNA 3’-CGCAUAC-5’5’
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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
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TRANSCRIPTIONTRANSCRIPTION
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 POLYMERASERNA POLYMERASE
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MRNA PROCESSINGMRNA PROCESSING
After the DNA is transcribed into RNA, editing must be done to the nucleotide chain to make the RNA functional
Introns, non-functional segments of DNA are snipped out of the chain
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MRNA EDITINGMRNA EDITING Exons, segments of DNA that code for proteins, are then rejoined by
the enzyme ligase A guanine triphosphate cap is added to the 5” end of the newly
copied mRNA A poly A tail is added to the 3’ end of the RNA The newly processed mRNA can then leave the nucleus
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38CAP
TailNew Transcript
Result of TranscriptionResult of Transcription
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•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
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TranscriptioTranscriptionn
TranslatiTranslationon
RIBOSOMESRIBOSOMES
Made of a large and small subunit
Composed of rRNA (40%) and proteins (60%)
Have two sites for tRNA attachment --- P and A
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STEP 1- INITIATIONSTEP 1- INITIATION
mRNA transcript start codon AUG attaches to the small ribosomal subunit
Small subunit attaches to large ribosomal subunit
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mRNA transcript
RIBOSOMESRIBOSOMES
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PSite
ASite
Largesubunit
Small subunit
mRNAmRNA
A U G C U A C U U C G
As ribosome moves, two tRNA with their amino acids move into site A and P of the ribosome
Peptide bonds join the amino acids
INITIATIONINITIATION
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mRNAmRNA
A U G C U A C U U C G
2-tRNA
G
aa2
A U
A
1-tRNA
U A C
aa1
anticodon
hydrogenbonds codon
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mRNAmRNA
A U G C U A C U U C G
1-tRNA 2-tRNA
U A C G
aa1 aa2
A UA
anticodon
hydrogenbonds codon
peptide bond
3-tRNA
G A A
aa3
ElongationElongation
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mRNAmRNA
A U G C U A C U U C G
1-tRNA
2-tRNA
U A C
G
aa1
aa2
A UA
peptide bond
3-tRNA
G A A
aa3
Ribosomes move over one codon
(leaves)
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mRNAmRNA
A U G C U A C U U C G
2-tRNA
G
aa1
aa2
A UA
peptide bonds
3-tRNA
G A A
aa3
4-tRNA
G C U
aa4
A C U
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mRNAmRNA
A U G C U A C U U C G
2-tRNA
G
aa1aa2
A U
A
peptide bonds
3-tRNA
G A A
aa3
4-tRNA
G C U
aa4
A C U
(leaves)
Ribosomes move over one codon
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mRNAmRNA
G C U A C U U C G
aa1aa2
A
peptide bonds
3-tRNA
G A A
aa3
4-tRNA
G C U
aa4
A C U
U G A
5-tRNA
aa5
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mRNAmRNA
G C U A C U U C G
aa1aa2
A
peptide bonds
3-tRNA
G A A
aa3
4-tRNA
G C U
aa4
A C U
U G A
5-tRNA
aa5
Ribosomes move over one codon
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mRNAmRNA
A C A U G U
aa1
aa2
U
primaryprimarystructurestructureof a proteinof a protein
aa3
200-tRNA
aa4
U A G
aa5
C U
aa200
aa199
terminatorterminator or stopor stop codoncodon
TerminationTermination
END PRODUCT –THE PROTEIN!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
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aa1
aa2 aa3 aa4aa5
aa200
aa199
MESSENGER RNA (MRNA)MESSENGER RNA (MRNA)
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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
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