Transcript DNA Replication

Ch. 11: DNA
Replication,
Transcription, &
Translation
Mrs. Geist
Biology, Fall 2010-2011
Swansboro High School
Replication of DNA
 When the cell divides, a complete set of genetic
instructions is generated for each new cell.
 When an organism reproduces, genetic instructions pass
from one generation to the next.
 For this to occur, DNA must copy.
 Template Mechanism
 Negative and photograph” – The cell uses a negative of DNA
to make more DNA.
Template Mechanism
DNA replication
 the 2 strands of the double helix separate using an enzyme.
 Each single strand serves as a “negative” for producing a new,
complementary strand.
 Nucleotides line up one at a time across from existing strand as
predicted by the base-pairing rules.
 A pairs with T
 C pairs with G
 Enzymes link the nucleotides together to form two new DNA
strands, called daughter strands.
From DNA to Protein
 “One Gene-One Polypeptide” Hypothesis- each gene
encodes the instructions to produce one polypeptide
 Bases are like the language’s letters
 Each gene is like a sentence
Ribonucleic acid (RNA)
 nucleic acid whose sugar is ribose
 Contains uracil (U) instead of thymine (T) in DNA
 Single-stranded, sometimes twisted
 Several RNA molecules are involved in the steps from gene to
protein
 Messenger RNA (mRNA)- brings instructions from DNA in the
nucleus to the ribosomes in the cytoplasm
 Ribosomal RNA (rRNA)- binds to mRNA and uses the instruction to
assemble AAs in the correct order
 Transfer RNA (tRNA)- delivers AAs to the ribosome to make a
protein
From DNA to Protein
 DNA is converted to RNA during the process of
transcription.
 Similar to a reporter transcribing a speech. The language
remains the same, however the form of the message changes
from spoken to written language.
 RNA is converted to an amino acid sequence in a process
called translation.
 Similar to translating English to Russian
 Codon- a 3-base word in mRNA that codes for one amino acid
 Several codons translate into amino acids that make up a
polypeptide
The Triplet Code
 Each codon stands for a particular amino acid
 64 different codons
 Note: some amino acids are coded for by more than one
codon. NO codon represents more than one amino acid.
 Start codon: signals to start translating an RNA transcript
 AUG or methionine (Met)
 Stop codon: DO NOT code for amino acids. Signal the end
of each genetic message. Stop translating.
 UAA or UAG or UGA- stop
The Triplet Code
Transcription: DNA to RNA
 DNA template is transcribed into a messenger RNA
(mRNA) in the nucleus
 Only one of the DNA strands serves as a template for mRNA
 2 DNA strands separate and then RNA bases pair with
complementary DNA bases
 Remember: substitute U for T in RNA
 A transcription enzyme links the RNA nucleotides
together
Editing the RNA message
 In prokaryotes, the mRNA directly serves as the
messenger that is transcribed into a protein
 In eukaryotes, the RNA transcribed is modified before it
leaves the nucleus as mRNA to be translated
 Introns- internal noncoding regions
 Exons- coding regions of the RNA transcript
 Before RNA leaves the nucleus, enzymes remove introns
and join exons together to produce the “final draft”
 Called RNA splicing
Translation: RNA to Protein
 Transfer RNA (tRNA)- transports and matches AAs to their
appropriate codons on the mRNA transcript
 Different version of tRNA molecule that matches each
codon.
 At the one end of the folded tRNA molecule is a specific
triplet of bases called an anticodon.
 At the other other end is a site where a particular AA can
attach.
tRNA
Translation: RNA to Protein
1. A ribosome attaches to the mRNA strand. Molecules of
tRNA, each carrying a specific AA, approach the
ribosome.
2. The start codon, AUG, signals the start of proteins
synthesis and codes for the AA methionine. The tRNA
carrying methionine attaches to the ribosome and mRNA
strand.
3. A new tRNA carrying an AA attaches to ribosome and
mRNA strand next to the previous tRNA. AAs join by
peptide bonds.
Translation: RNA to Protein
4. Ribosome slides along the mRNA to the next codon and
the old tRNA molecule is released. A new tRNA molecule
carrying an AA can attach to ribosome and mRNA strand.
5. Repeat steps 2-4 until a stop codon is reached on the
mRNA strand.
Translation: RNA to Protein