introduction to central dogma: dna replication, transcription and translation
TRANSCRIPT
Introduction to Central Dogma:
DNA Replication, Transcription and Translation
What is Central Dogma?
• It is the flow of genetic information from DNA to Proteins
Transcription Translation
DNA mRNA Proteins
Replication
DNA
What is DNA?
• It is the fascinating molecule that contains the Codeof Life.
• It is the Genetic Code, which is the set of “messages” that are “translated” by ribosomes into proteins that define YOU
What Is the Code of Life?
• Recall that DNA and RNA belong to the class of biomolecules called Nucleic Acids, which are made up of nucleotide monomers
Structure of Nucleic Acids
The nucleotide subunits consist of:
1. A Nitrogen Base
2. A Sugar (either Deoxyribose or Ribose)
3. A Phosphate Group
Structure of Nucleotides
Nitrogen Bases Can Be:
Adenine
Guanine
Cytosine
Thymine (only DNA)
Uracil (only RNA)
Nitrogen Bases
A
G
C
T
U
Erwin Chargaff analyzed DNA from different organisms and found that
A = T & G = C
Chargaff’s Rule of Base Pairing
According to Chargaff, in DNA:
A always bonds with T G always bonds with C
Image by: Riedell
The Sugar Group Can Be Either:
Deoxyribose (in DNA)or-
Ribose (in RNA)
The Sugar Group
Purines consist of Adenine and Guanine bases; they are double-ring structures
Pyrimidines consist of Thymine and Guanine bases; they are single-ring structures
A Purine ALWAYS bonds with a Pyrimidine….A with T and G with C
Purines & Pyrimidines
DNA has no URACIL RNA has no THYMINE
Nitrogen Base Difference DNA & RNA
• The nitrogen bases are held together by weak hydrogen bonds
• The sugar and phosphate groups are held together by strong covalent phosphodiester bonds
Bonding in DNA
CovalentPhosphodiester
Bonds
Semi-Conservative:•Strand separation, followed by copying of each strand. •Each separated strand acts as a template for the synthesis of a new complementary strand.
DNA Replication (occurs in the nucleus)
Step 1:•Unwinding of the double helix
Helicase enzyme unwinds the double helix & creates a replication fork
DNA Replication (occurs in the nucleus)
Step 2:•One DNA strand is used as a template to create the new copy DNA DNA A – T G – C C – G A – T A – T etc
DNA Replication (occurs in the nucleus)
• Transcription produces genetic messages in the form of mRNA
DNA Transcription (occurs in the nucleus)
DNA Template
mRNA
• STEP 1: As in replication, the DNA double helix unzips
• STEP 2: RNA nucleotides line up along one strand of DNA, following the base-pairing rules
DNA Transcription (occurs in the nucleus)
DNA Template
mRNA
• STEP 3: DNA is transcribed into RNA
DNA mRNA G C T A A U G G G C T A
DNA Transcription (occurs in the nucleus)
DNA Template
mRNA
• Single-stranded mRNA peels away from DNA and prepares to move into the cytoplasm
DNA Transcription (occurs in the nucleus)
DNA
mRNA
Nucleus
Cytoplasm
• Eukaryotic RNA is processed before leaving the nucleus
The non-coding segments, called introns, are spliced out
A cap & tail are added to the ends
DNA Transcription (occurs in the nucleus)
Exon Exon ExonIntron Intron
Introns removed
Exons spliced together
Coding sequence
mRNA
DNA
RNAtranscriptwith capand tail
TranscriptionAddition of cap and tail
NUCLEUS
CYTOPLASM
Cap
Tail
• mRNA leaves the nucleus and moves into the cytoplasm where it will be “translated” into a polypeptide (a fancy word for a protein)
DNA Translation (occurs in the cytoplasm)
TRANSCRIPTION
TRANSLATION
PROTEIN
CYTOPLASM
NUCLEUS
• The words that will be translated are triplets of mRNA bases called codons
• The codons in a gene determine the amino acids in the polypeptide sequence
DNA Translation (occurs in the cytoplasm)
DNA molecule
DNA strand
TRANSCRIPTION
RNA
TRANSLATION
PolypeptideAmino acid
Gene 1
Gene 2
Gene 3
Codon Codon Codon Codon
• In the cytoplasm, a ribosome attaches to the mRNA • A tRNA pairs with each codon, adding an amino acid
to the growing polypeptide
DNA Translation (occurs in the cytoplasm)
U C A G
U
C
A
G
GACU
GACU
GACU
GACU
UUUUUCUUAUUG
CUUCUCCUACUG
AUUAUCAUAAUG
GUUGUCGUAGUG
phe
leu
leu
ile
met (start)
val
UCUUCCUCAUCG
CCUCCCCCACCG
ACUACCACAACG
GCUGCCGCAGCG
ser
pro
thr
ala
UAUUACUAAUAG
CAUCACCAACAG
AAUAAC
AAGAAA
GAUGACGAAGAG
tyr
stopstop
his
gln
asn
lys
asp
glu
UGUUGCUGAUGG
CGUCGCCGACGG
AGUAGCAGAAGG
GGUGGCGGAGGG
cys
stoptrp
arg
ser
arg
gly
First Base T
hird Base
Second Base
mRNA Genetic Code Chart
Table 14.2Types of RNA
Type of RNA Functions in Function
Messenger RNA(mRNA)
Nucleus, migratesto ribosomesin cytoplasm
Carries DNA sequenceinformation to ribosomes
Transfer RNA(tRNA)
Cytoplasm Provides linkage between mRNAand amino acids;transfers aminoacids to ribosomes
Ribosomal RNA(rRNA)
Cytoplasm Structural component of ribosomes
• Mutations are changes in the DNA base sequence Are caused by errors in DNA replication Are caused by environmental factors, such as
exposure to radiation and chemicals or temperature changes
• Mutations most likely cause altered proteins to be produced
• 2 Kinds of Mutations: Gene Mutations & Chromosomal Mutations
Mutations
• Point mutations – changes of a single DNA nucleotide – can cause sickle-cell anemia and many other disorders
Gene Mutations
Normal hemoglobin DNA Mutant hemoglobin DNA
mRNA mRNA
Normal hemoglobin Sickle-cell hemoglobin
Glu Val
• Types of Point mutations
Substitutions
Insertions
Deletions
Gene Mutations
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
mRNA
NORMAL GENE
BASE SUBSTITUTION
BASE DELETION
Protein Met Lys Phe Gly Ala
Met Lys Phe Ser Ala
Met Lys Leu Ala His
Missing
Gene Mutations
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Deletion
Duplication
Inversion
Homologouschromosomes
Reciprocaltranslocatio
nNon-homologouschromosomes
Chromosomal Mutations
• Human karyotype showing addition of 1 chromosome on autosome 21 – Down Syndrome
Chromosomal Mutations
Chromosome painting