Download PPT NOTES_AP Biology Chapter 17 Notes

AP Biology Chapter 17 Notes
From Gene to Protein
What you need to know…
• The key terms ____________ expression, ____________________, and _________________.
• How to explain the process of __________________.
• How eukaryotic cells modify _________ after transcription.
• The steps to __________________.
• How _______________ mutations can change the amino acid sequence of a protein.
Concept 17.1: Genes specify proteins via transcription and translation
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________________________ is the synthesis of RNA under the direction of DNA
• Transcription produces messenger RNA (___________)
_______________ is the synthesis of a polypeptide, which occurs under the direction of mRNA
• ____________________ are the sites of translation
Label the Picture
___________________________: a series of nonoverlapping, three-nucleotide words
• Example: AGT at a particular position on a DNA strand results in the placement of the amino acid
serine at the corresponding position of the polypeptide to be produced
During transcription, one of the two DNA strands called the ______________________ strand provides a
template for ordering the sequence of nucleotides in an RNA transcript
During translation, the mRNA base triplets, called _________________, are read in the 5 to 3 direction
• Each codon specifies the ____________________________ to be placed at the corresponding
position along a polypeptide
• Codons must be read in the correct _____________________________ (correct groupings) in order
for the specified polypeptide to be produced
Concept 17.2: Transcription is the DNA-directed synthesis of RNA: a closer look
• RNA synthesis is catalyzed by _____________________________, which pries the DNA strands
apart and hooks together the RNA nucleotides
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RNA synthesis follows the same base-pairing rules as DNA, except __________________
substitutes for _________________
• The DNA sequence where RNA polymerase attaches is called the __________________________;
in bacteria, the sequence signaling the end of transcription is called the _______________________
• The stretch of DNA that is transcribed is called a ________________________ unit
• 3 Stages of Transcription:
 Initiation
 In Bacteria – RNA polymerase recognizes and binds to the _______________
 In eukaryotes – RNA polymerase II (specific RNA polymerase that transcribes
mRNA) cannot bind to the promoter without supporting help from proteins known as
_____________ _________________________
 Transcription factors – assist binding of RNA polymerase to promoter and thus,
initiation of transcription
 Transcription ______________________ Complex – RNA Polymerase II and
transcription factors
 Elongation
 RNA ____________________ moves along the DNA, continuing to untwist double
helix
 RNA ___________________________ continually added to 3’ end of growing chain
 As complex moves down the DNA strand, double helix re-forms, with new RNA
molecule straggling away from the DNA template
 Termination
 In bacteria, the _____________________ stops transcription at the end of the
terminator
 In eukaryotes, after RNA polymerase transcribes a ________________________
sequence in the DNA, the RNA transcript is released
 Polymerase detaches
Concept 17.3: Eukaryotic cells modify RNA after transcription
• Enzymes in the eukaryotic nucleus _________________ pre-mRNA before the genetic messages are
dispatched to the cytoplasm
• During RNA processing, both ___________ of the primary transcript are usually altered
• Also, usually some interior parts of the molecule are ________________, and the other parts
___________________ together
• Each end of a pre-mRNA molecule is modified in a particular way:
 The 5 end receives a modified nucleotide _________________
 The 3 end gets a ___________________
• These modifications share several functions:
 They seem to facilitate the ______________ of mRNA
 They __________________ mRNA from hydrolytic enzymes
 They help ___________________ attach to the 5 end
• Most eukaryotic genes and their RNA transcripts have long noncoding stretches of nucleotides that lie
between coding regions - called intervening sequences, or ______________________
• The other regions are called _____________________ because they are eventually expressed, usually
translated into amino acid sequences
• ___________________________________ removes introns and joins exons, creating an mRNA
molecule with a continuous coding sequence
• ______________________________ consist of a variety of proteins and several small nuclear
ribonucleoproteins (___________________) that recognize the splice sites
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_______________________ are catalytic RNA molecules that function as enzymes and can splice RNA
Concept 17.4: Translation is the RNA-directed synthesis of a polypeptide: a closer look
• A cell translates an mRNA message into protein with the help of _______________ RNA (tRNA)
• Molecules of tRNA are not identical:
 Each carries a specific ________________ on one end
 Each has an _________________ on the other end; the anticodon base-pairs with a
complementary codon on mRNA
• Accurate translation requires two steps:
 First: a correct match between a tRNA and an amino acid, done by the enzyme aminoacyl-tRNA
____________________
 Second: a correct match between the tRNA _________________ and an mRNA ___________
• Flexible pairing at the third base of a codon is called ___________________ and allows some tRNAs to
bind to more than one codon
• Ribosomes:
 facilitate specific coupling of tRNA anticodons with mRNA codons in protein synthesis
 The _____________ ribosomal subunits (large and small) are made of proteins and ribosomal
RNA (____________)
 3 Binding Sites for tRNA:
 The _____ site holds the tRNA that carries the growing polypeptide chain
 The _____ site holds the tRNA that carries the next amino acid to be added to the chain
 The _____ site is the exit site, where discharged tRNAs leave the ribosome
• 3 Stages of Translation:
 Initiation
 Small ribosomal subunit binds to mRNA so that the first ___________ of the mRNA
strand, which is always AUG, is placed in proper position
 tRNA with anticodon UAC (carries amino acid methionine), hydrogen bonds to first
codon (initiation factors are proteins that assist in holding all this together.
 Large subunit of ribosome ________________, allowing the tRNA with methionine to
attach to the P site. A site is now available for a new tRNA.
 Elongation
 Codon recognition – codon in A site is matched by incoming tRNA ______________
 _______________ bond formation - incoming aa in the A site forms peptide bond with
existing chain of amino acids held in the P site. Bond is catalyzed by rRNA and is
example of a ribozyme.
 ___________________ – occurs when tRNA in A site is moved to P site, and tRNA in P
site is moved to E site, where it is released
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 Termination
 Termination occurs when a ____________ codon in the mRNA reaches the A site of the
ribosome
 The A site accepts a protein called a ________________________________
 The release factor causes the addition of a water molecule instead of an amino acid
 This reaction releases the polypeptide, and the translation assembly then comes apart
 A number of ribosomes can translate a single mRNA simultaneously, forming a
_______________________________ (or polysome)
Concept 17.5: Point mutations can affect protein structure and function
• ____________________ are changes in the genetic material of a cell or virus
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__________________ mutations are chemical changes in just one base pair of a gene
 Point mutations within a gene can be divided into two general categories
 Base-pair ___________________________
 Base-pair _________________ or __________________
 A base-pair __________________________ replaces one nucleotide and its partner with
another pair of nucleotides
 Silent mutations have ___________ effect on the amino acid produced by a codon because of
redundancy in the genetic code
 _____________________ mutations still code for an amino acid, but not necessarily the right
amino acid
 _____________________ mutations change an amino acid codon into a stop codon, nearly
always leading to a nonfunctional protein
 __________________ and ____________________ are additions or losses of nucleotide pairs in
a gene
 Insertion or deletion of nucleotides may alter the reading frame, producing a
________________________________
 _______________________ are physical or chemical agents that can cause mutations
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