Genes Expression or Genes and How They Work: Transcription, Translation, & More
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Central Dogma
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During polypeptide synthesis, ______________________ is the site of polypeptide assembly.
– _____________________________________ transports and positions amino acids.
– ________________________ directs which amino acids are assembled into polypeptides
Proposed by _________________________ in 1958 to describe the flow of information in a cell.
Information stored in DNA is transferred residue-by-residue to RNA which in turn transfers the
information residue-by-residue to protein.
The Central Dogma was proposed by Crick to help scientists think about molecular biology.
It has undergone numerous revisions in the past 45 years.
Transcription Overview
Def: DNA sequence is _________________________ into RNA sequence
– initiated when ________________________ binds to promoter binding site
– moves along DNA strand and adds ________________________________ nucleotide
 disengages at _______________
Translation Overview
Def: nucleotide sequence of ___________________ is translated into _______________________
sequence in the polypeptide
– rRNA recognizes and binds to start sequence
– moves three nucleotides at a time
 disengages at stop signal
– Gene expression - ___________________________________________
Genetic Code
• How does the order of nucleotides in a DNA molecule encode the information that specifies the
order of amino acids in a polypeptide?
• The answer came in 1961 through an experiment lead by ______________________.
• Crick and colleagues reasoned that there must be _________________ or block of info that
coded for an amino acid
• They hypothesized that it was most likely _____________________
– Why 3?
– 2 nucleotides did not have enough combinations (____________________________)
– 3 nucleotides (___________) which is enough to cover the roughly 20 known amino acids
• Now known
• Genetic code consists of a series of information blocks called __________________.
– reading frame (__________________)
• each codes for one amino acid
• highly redundant
• Could be _________________________
• Punctuated code would have a ________________________ that separates codons
• Non-punctuated code would _____________
• In the following example, O is not a base pair but the “______________________”
• Crick concluded that it is not punctuated as _____________________________________
_______________________________.
• Code is practically ______________
• ex: AGA codes for arginine in ___________________________________________
• great evidence that all life has ____________________________
• Genes coded in one organism can be ____________________________
– SWEET biotechnology
• Code is practically universal…____________________
• In 1979 mammalian mitochondria found to have a ___________________________
– In mitochondrial DNA, UGA is not a stop codon as it is in “universal code”
– Other codons are different
– Chloroplasts and ciliates (protists) have ______________________________
• It is thought that the changes to _____________________________________________
__________________________________
More on RNA
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– Central Dogma shows ___________________________________________________
RNA’s structure is different from DNA
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RNA Structure
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Both DNA and RNA contain four nitrogenous bases, but rather than thymine, RNA contains a
similar base called uracil (U).
Transcription
• RNA polymerase
– only one of two DNA strands (template or antisense strand) is transcribed
– non-transcribed strand is termed coding strand or sense strand
– In both bacteria and eukaryotes, the polymerase adds ribonucleotides to the growing 3’ end
of an RNA chain.
 synthesis proceeds in 5’3’ direction
Transcription Bubble
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Promoter
– Transcription starts at ____________________binding sites called __________________
on DNA template strand.
Initiation
– Other eukaryotic factors bind, assembling a ___________________________.
 RNA polymerase begins to ___________________________.
Elongation
– Transcription bubble moves ___________________ at constant rate leaving ___________
strands protruding from the bubble.
Termination
– Stop sequences at the end of the gene cause ___________________________ formation
to cease, ______________________ to dissociate, and RNA polymerase to ___________.
Transcription Process Video (we will watch this twice!!)
– For RNA polymerase to successfully bind to a eukaryotic _______________ and initiate
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transcription, a set of proteins called ___________________ must first assemble on the promoter.
The assembly process begins _________________ from the transcription start site, where
proteins called ____________________ bind to a short TATA sequence in the promoter.
Other basal factor proteins then bind, eventually forming a full ________________________ able
to capture the RNA polymerase.
Basal factors are essential for transcription but cannot by themselves increase or decrease its
rate. A second set of transcription factors called coactivators link the basal factor proteins called
activators.
Activators are ________________________ that bind to sequences on DNA called enhancers.
Enhancers are located at sites that are ________________________________________.
The interaction of activator proteins with transcription factor subunits ___________________ of
transcription.
Many enhancers, scattered around the chromosome, can bind different activators, which provide a
variety of responses to various signals.
When a second kind of regulatory protein called a repressor binds to a “silencer” sequence
located adjacent to or overlapping an enhancer sequence, the corresponding activator is not
longer able to bind to the DNA.
Eukaryotic Transcription
• Eukaryotic transcription differs from ______________________ transcription:
What is the difference between eukaryotes and prokaryotes again?
– ________________________ enzymes
– ___________________________ at promoter
– RNAs are _________________ after transcription
Translation: From mRNA to Protein
• The process of converting the _________________ in a sequence of _______________________
into a sequence of ________________________________ is known as ____________________.
• Translation takes place at the ________________________________________________.
The role of transfer RNA
• For proteins to be built, the ________________________ dissolved in the cytoplasm must be
brought to the __________________.
• This is the role of ___________________
• Each ____________________ attaches to only one type of ______________.
• The first codon on _______________________, which codes for the amino acid methionine
• _____________ signals the start of ______________________.
• When this signal is given, the ___________________ along the ___________ to the next _______.
• A new ___________________ carrying an amino acid ______________ with the second
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The amino acids are joined when a ____________________________ is formed between them.
A chain of amino acids is formed until the _______________ is reached on the ______________.
Translation (in more detail)
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Begins when initial portion of ____________________ binds to _______________________
– __________________ molecule with complimentary _____________________ binds to
exposed codon ________________
 some _________ molecules recognize more than ________________
Activating enzymes
– tRNA molecules attach to ____________________ through the action of ______________
___________ (aminoacyl-tRNA syntheases).
 must correspond to specific anticodon ________________________ molecule as
well as particular __________________Start and stop signals
– start signal coded by ____________________
– stop signal coded by one of three ___________________: _____________________
 What do you think “nonsense codons” means here?
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Initiation
– ______________________________ begins with the formation of an initiation complex.
 initiation factors
• Elongation
– After initiation complex forms, _______________ subunit binds, exposing ____________
adjacent to the initiating codon, positioning it for interaction with another amino acid-bearing
____________________.
• Translocation
– ________________ moves nucleotides along __________________
A bit about the peptide bond formation
• A peptide bond (amide bond) is a ___________________ chemical bond formed between two
molecules when the ______________________ of one molecule reacts with the
__________________ of the other molecule, thereby releasing a __________.
• This is a ______________________ reaction (also known as a _________________________),
and usually occurs between ___________________.
• The resulting C(O)NH bond is called a _________________, and the resulting molecule is ______.
• The four-atom functional group -C(=O)NH- is called a ___________________
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Termination
– ___________________ are recognized by release factors that release the newly made
_________________________________.
– There is _____________ with complimentary antidcodon to (UAA, UAG, UGA)
Spliced Gene Transcripts
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DNA sequence specifying a protein is broken into segments _______________ scattered among
longer noncoding segments _________________.
Initially, ___________________ is produced for the _________________.
– Small nuclear ribonuclearproteins (_______) associate with proteins to form ___________.
 Lariat forms, _________________ and _______________ to form _____________.
 ________________________
How Spliceosomes Process RNA (we will watch this twice!!)
– Most eukaryotic genes are composed of numerous ______________________ called exons,
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embedded within stretches of __________________________ called introns.
The initial messenger RNA molecule or _________________________ copied from a gene by
RNA polymerase, is a faithful copy of ________________, including _______________________.
Before the primary transcript is ________________, the introns are removed by a process called
__________________________________.
Particles composed of proteins and a special types of RNA called small nuclear RNA, or _______,
play a role in RNA splicing.
One kind of small nuclear ribonucleoprotein (snRNP) contains snRNA that can bind to the ______
of an intron by forming base-pairs with complementary sequences on the ________. A different
snRNP binds to the _____________________.
Additional introns interact, causing the intron to _______________, thereby bringing the two ends
of the intron together.
The large complex of snRNPs, called a ___________________, then _______________ and the
exons are joined together. The snRNPs are then released.
• During RNA processing, intron sequences are _________________________ before it is used in
polypeptide synthesis.
– remaining sequences are ____________________
 remaining exon sequences are _________________ to form final ______________________
An Overview of Eukaryotic Gene Expression
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Differences Between Prokaryotic and Eukaryotic Gene Expression
• Most ______________ genes possess introns (prokaryotic genes do not.)
• Individual ________________ molecules often contain transcripts of ____________________.
• Eukaryotic mRNA molecules must be __________________ and must pass across the _________
___________ before translation.
• In prokaryotes, translation begins at the AUG codon preceded by a special nucleotide sequence.
• Eukaryotic mRNA molecules have introns cut out and exons joined together before ____________.
• Eukaryotic ribosomes are larger than prokaryotic ribosomes.
How do mutation effect proteins
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Any change in DNA sequence is called a ___________________.
Mutations can be caused by errors in ____________________________________________
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The effects of point mutations
• A point mutation is a change in a ________________________ in DNA
• A change in a single nitrogenous base can change the entire structure of a protein because a
change in a single amino acid can affect the _______________________________
Frameshift mutations
• A mutation in which a single base is __________________ from DNA is called a frameshift
mutation because it _______________ the reading of codons by one base.
• Structural changes in chromosomes are called __________________________
Causes of Mutations
• Any agent that can cause a change in DNA is called a mutagen.
• Mutagens include radiation, chemicals, and even high temperatures
• Forms of radiation, such as X rays, cosmic rays, ultraviolet light, and nuclear radiation, are
dangerous mutagens because the energy they contain can damage or break apart
Chromosomal Alterations
• When a part of a chromosome is _______________, a deletion occurs.
A B C D E
F G H
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B C E
F G H
Deletion
• When part of a chromatid ________________ to its sister chromatid, an insertion occurs.
• The result is a duplication of ______________________________ chromosome
A B C D E
F G H
A B C B C D E
F G H
Insertion
• When part of a chromosome breaks off and reattaches backwards, an ______________________.
A B C D E
F G H
A B C B C D E
F G H
Insertion
• When part of one chromosome breaks off and is added to a different chromosome, a ___________
_____________.
AB C D E F GH
WX Y Z
W X AB C DE F GH
Translocatio
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Z