Transcript of Chapter 10 DNA TRANSCRIPTION and TRANSLATION. THE FLOW OF GENETIC INFORMATION FROM DNA TO RNA TO...
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- Chapter 10 DNA TRANSCRIPTION and TRANSLATION
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- THE FLOW OF GENETIC INFORMATION FROM DNA TO RNA TO PROTEIN WARM
UP What are proteins? Where do they come from?
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- THE FLOW OF GENETIC INFORMATION FROM DNA TO RNA TO PROTEIN DNA
in our cells carry the instructions for making proteins in order
for our cells to function.
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- How an Organisms Genotype Determines Its Phenotype An organisms
genotype is its genetic makeup, the sequence of nucleotide bases in
DNA. The phenotype is the organisms physical traits, which arise
from the actions of a wide variety of proteins.
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- DNA specifies the synthesis of proteins in two stages: 1.
transcription, the transfer of genetic information from DNA into an
RNA molecule 2. translation, the transfer of information from RNA
into a protein. How an Organisms Genotype Determines Its
Phenotype
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- Central Dogma Polypeptide TRANSCRIPTION mRNA DNA Gene
TRANSLATION
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- Figure 10.8-3 DNA Cytoplasm Nucleus RNA Protein TRANSCRIPTION
TRANSLATION
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- Back to chapter 3!!!! RNA = ribonucleic acid (ribose sugar)
Instead of THYMINE, RNA has URACIL Single strand RNA Overview
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- mRNA = messanger RNA tRNA = transfer RNA rRNA = ribosomal RNA 3
Types of RNA
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- mRNA = messanger RNA made by transcription of the original DNA
molecule a messanger from the DNA to the rest of the cell. 3 Types
of RNA
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- tRNA = transfer RNA interpreter, converts the language in mRNA
into the language of proteins (amino acid monomers) 3 Types of
RNA
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- rRNA = ribosomal RNA rRNA is combined with proteins to form a
ribosome, which is the site of protein synthesis coordinate the
functions of mRNA and tRNA 3 Types of RNA
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- Figure 10.10a Amino acid RNA DNA strand Polypeptide Codon
TRANSCRIPTION TRANSLATION
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- DNA to mRNA Problems Given the DNA sequence, construct an mRNA
for the following pieces of DNA. TTCAGCGATACCGTAGGA
TACCCCGTATTGGAAATT AAACCGGCAAAATTGCTC
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- Transcription: From DNA to RNA Transcription makes mRNA from a
DNA template, substitutes uracil (U) for thymine (T). uses a
process that resembles the synthesis of a DNA strand during DNA
replication Lets take a closer look at this process!!!
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- Transcription: From DNA to RNA THE BIG PICTURE Transfer of
genetic information from DNA to RNA resembles the process of DNA
replication! Only 1 strand of DNA is used as a template for mRNA
synthesis. RNA nucleotides are linked by the transcription enzyme
RNA polymerase. End result is mRNA!!!
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- Figure 10.13a Newly made RNA RNA nucleotides Template strand of
DNA (a) A close-up view of transcription RNA polymerase
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- STEP 1: Initiation of Transcription The start transcribing
signal is a nucleotide sequence called a promoter located in the
DNA sequence at the beginning of the gene which is being
transcribed. a specific place where RNA polymerase attaches. The
first phase of transcription is initiation, in which RNA polymerase
attaches to the promoter. RNA synthesis begins.
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- STEP 2: RNA Elongation Elongation, the second phase of
transcription the RNA grows longer the RNA strand peels away from
its DNA template.
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- STEP 3: Termination of Transcription Termination, third phase
of transcription RNA polymerase reaches a special sequence of bases
in the DNA template called a terminator, signaling the end of the
gene polymerase detaches from the RNA and the gene (DNA) the DNA
strands rejoin.
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- Figure 10.13b (b) Transcription of a gene RNA polymerase
Completed RNA Growing RNA Termination Initiation Terminator DNA
Elongation RNA Promoter DNA RNA polymerase DNA of gene 213
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- The Processing of Eukaryotic RNA Sowe now have an RNA
strand.now what? Prokaryotic cells RNA transcribed from a gene
immediately functions as messenger RNA (mRNA), the molecule that is
translated into protein. Eukaryotic cells localizes transcription
in the nucleus (because they have one!!) modifies, or processes,
the RNA transcript in the nucleus before it move to the cytoplasm
for translation by a ribosome.
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- RNA processing includes adding a cap and tail consisting of
extra nucleotides at the ends of the RNA transcript helps to
protect the RNA from enzyme attack! help ribosomes recognize RNA as
mRNA. removing introns (noncoding regions of the RNA) RNA splicing,
joining exons (the parts of the gene that are expressed) together
to form messenger RNA (mRNA). The Processing of Eukaryotic RNA
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- Figure 10.14 Transcription Addition of cap and tail Coding
sequence mRNA DNA Cytoplasm Nucleus Exons spliced together Introns
removed Tail Cap RNA transcript with cap and tail Exon Intron
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- RNA splicing is believed to play a significant role in humans
in allowing our approximately 21,000 genes to produce many
thousands more polypeptides by varying the exons that are included
in the final mRNA. The Processing of Eukaryotic RNA
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- The flow of information from gene to protein is based on a
triplet code. A codon is a triplet of bases, which codes for one
amino acid. From Nucleotides to Amino Acids: An Overview
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- The Genetic Code The genetic code is the set of rules that
convert a nucleotide sequence in RNA to an amino acid sequence. Of
the 64 triplet codes, 61 code for amino acids 3 are stop codons,
instructing the ribosomes to end the polypeptide.
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- Figure 10.11 Second base of RNA codon First base of RNA codon
Phenylalanine (Phe) Leucine (Leu) Cysteine (Cys) Leucine (Leu)
Isoleucine (Ile) Valine (Val) Met or start Serine (Ser) Proline
(Pro) Threonine (Thr) Tyrosine (Tyr) Histidine (His) Glutamine
(Gln) Asparagine (Asn) Alanine (Ala) Stop Glutamic acid (Glu)
Aspartic acid (Asp) Lysine (Lys) Arginine (Arg) Tryptophan (Trp)
Arginine (Arg) Serine (Ser) Glycine (Gly) Third base of RNA codon
UUU UUC UUA UUG UAU UAC CAU CAC CAA CAG AAU AAC AAA AAG GAU GAC GAA
GAG UGU UGC AGU AGC AGA AGG GGU GGC GGA GGG CGU CGC CGA CGG GCU GCC
GCA GCG ACU ACC ACA ACG CCU CCC CCA CCG UCU UCC UCA UCG CUU CUC CUA
CUG GUU GUC GUA GUG AUU AUC AUA AUG UAA UAG UGA UGG UCAG U C A G
UCAGUCAG UCAGUCAG UCAGUCAG UCAGUCAG
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- The genetic code is almost universal Because diverse organisms
share a common genetic code, it is possible to program one species
to produce a protein from another species by transplanting DNA. The
Genetic Code
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- Translation Translation is the conversion from nucleic acid to
protein. Involves three crucial players mRNA result of
transcription, direct message from DNA tRNA molecular interpreter,
carries amino acids rRNA makes up a ribosome, which coordinates
mRNA and tRNA functions
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- Translation: requirements Translation requires mRNA ATP enzymes
ribosomes transfer RNA (tRNA)
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- Transfer RNA (tRNA) matches amino acids with codons in mRNA
using anticodons, a special triplet of bases that is complementary
to a codon triplet on mRNA.
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- Figure 10.15 tRNA polynucleotide (ribbon model) Anticodon
Hydrogen bond Amino acid attachment site tRNA (simplified
representation) RNA polynucleotide chain
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- Ribosomes Ribosomes are organelles that coordinate the
functions of mRNA and tRNA are made of two subunits. Each subunit
is made up of proteins ribosomal RNA (rRNA).
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- Figure 10.16b Next amino acid to be added to polypeptide
Growing polypeptide tRNA mRNA (b) The players of translation
Codons
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- Translation: The Process Translation is divided into three
phases: 1.initiation 2.elongation 3.termination
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- Initiation Initiation brings together mRNA, tRNA and the two
subunits of the ribosome (rRNA) The mRNA molecule has a cap and
tail that help the mRNA bind to the ribosome. The pink portion also
helps the mRNA bind to the ribosome.
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- Initiation occurs in two steps. 1.An mRNA molecule binds to a
small ribosomal subunit, then a special initiator tRNA binds to the
start codon AUG codon, UAC - anticodon, 2.A large ribosomal subunit
binds to the small one, creating a functional ribosome.
Initiation
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- Elongation Elongation occurs in three steps. Step 1: Codon
recognition. The anticodon of an incoming tRNA pairs with the mRNA
codon at the A site of the ribosome.
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- Figure 10.19 Amino acid Anticodon A site Codons mRNA P site
Polypeptide Codon recognition Peptide bond formation Translocation
Stop codon New peptide bond mRNA movement 2 1 3 ELONGATION
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- Step 2: Peptide bond formation. The polypeptide leaves the tRNA
in the P site and attaches to the amino acid on the tRNA in the A
site. The ribosome catalyzes the bond formation between the two
amino acids. Elongation
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- Step 3: Translocation. The P site tRNA leaves the ribosome. The
tRNA carrying the polypeptide moves from the A to the P site.
Elongation
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- Termination Elongation continues until a stop codon reaches the
ribosomes A site, the completed polypeptide is freed, and the
ribosome splits back into its subunits.
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- Review: DNA RNA Protein In a cell, genetic information flows
from DNA to RNA in the nucleus RNA to protein in the cytoplasm. As
it is made, a polypeptide coils and folds and assumes a
three-dimensional shape. Determines the appearance and capabilities
of the cell and organism. Transcription and translation are how
genes control the structures and activities of cells.
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- Figure 10.20-6 Transcription RNA polymerase mRNA DNA Intron
Nucleus mRNA Intron Tail Cap RNA processing tRNA Amino acid Amino
acid attachment Enzyme ATP Initiation of translation Ribosomal
subunits Termination Anticodon Codon Elongation Polypeptide Stop
codon Anticodon A 346521
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- HOW AND WHY GENES ARE REGULATED Every somatic cell (body cell,
not sex cell) in an organism contains identical genetic
instructions. They all share the same genome. So what makes cells
different from one another?
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- In cellular differentiation, cells become specialized in
structure and function. Certain genes are turned on and off in the
process of gene regulation. HOW AND WHY GENES ARE REGULATED
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- Patterns of Gene Expression in Differentiated Cells In gene
expression, a gene is turned on and transcribed into RNA
information flows from genes to proteins genotype to phenotype.
Information flows from DNA to RNA to proteins. The great
differences among cells in an organism must result from the
selective expression of genes.
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- Gene Regulation in Bacteria Natural selection has favored
bacteria that express only certain genes only at specific times
when the products are needed by the cell. E. coli living in your
intestines survive on what you eat, adjusting production of enzymes
as needed for digestion of various food items. So how do bacteria
selectively turn their genes on and off?
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- An operon includes a cluster of genes with related functions
the control sequences that turn the genes on or off. The bacterium
E. coli uses the lac operon to coordinate the expression of genes
that produce enzymes used to break down lactose in the bacteriums
environment. Gene Regulation in Bacteria
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- The lac operon uses a promoter, a control sequence where the
transcription enzyme attaches and initiates transcription an
operator, a DNA segment that acts as a switch that is turned on or
off a repressor (protein), which binds to the operator and
physically blocks the attachment of RNA polymerase and
transcription. Gene Regulation in Bacteria
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- Figure 11.2 Operon turned on (lactose inactivates repressor)
Lactose Protein mRNA DNA Protein mRNA DNA Operon turned off
(lactose absent)
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- Figure 11.2a Protein mRNA DNA Operon turned off (lactose
absent) Active repressor RNA polymerase cannot attach to promoter
Regulatory gene Promoter Operon Genes for lactose enzymes Operator
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- Figure 11.2b Operon turned on (lactose inactivates repressor)
Lactose Protein mRNA Lactose enzymes DNA Translation Inactive
repressor RNA polymerase bound to promoter Transcription 21345
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- Gene Regulation in Eukaryotic Cells Eukaryotic cells have more
complex gene regulating mechanisms with many points where the
process can be turned on or off. The multiple mechanisms that
control gene expression are like the many control valves along a
water supply.
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- Mutations A mutation is any change in the nucleotide sequence
of DNA.
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- Mutations can change the amino acids in a protein. Mutations
can involve large regions of a chromosome just a single nucleotide
pair, as occurs in sickle-cell disease. Mutations
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- Mutations within a gene can be divided into two general
categories: 1.nucleotide substitutions (the replacement of one base
by another) 2.nucleotide deletions or insertions (the loss or
addition of a nucleotide). Types of Mutations
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- Nucleotide substitutions can be divided into 3 different type
of mutations. Silent mutation = change in the nucleotide may
transform one codon into another but due to the redundancy of the
genetic code, is translated into the same amino acid. Missense
mutation = change in the nucleotide when translated, changes one
amino acid into another. May or may not be detrimental to the
proteins function. (sickle cell anemia) Nonsense mutation = change
in the nucleotide that changes a codon for an amino acid into a
stop codon. Types of Mutations
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- Nucleotide insertions and deletions can change the reading
frame of the genetic message lead to disastrous effects. can alter
the reading frame of the genetic message = frameshift mutations.
Types of Mutations
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- Mutagens Mutations may result from errors in DNA replication
physical or chemical agents called mutagens. X-rays UV light
Mutations are often harmful but are useful in nature and the
laboratory as a source of genetic diversity, which makes evolution
by natural selection possible!!!