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Reading Notes Chapter 17
p. 326
One the basis of experiments with mutants of Bread mold, Beadle and Tatum proposed
the one gene ____ _________________ hypothesis.
Basic Principles of Transcription and Translation, p. 328
Transcription is the synthesis of ________ under the direction of _______.
______________________ _______ (mRNA) carries a genetic message from the ______
to the protein-synthesizing machinery of the cell.
______________________ is the actual synthesis of a polypeptide , which occurs under
the direction of the mRNA. During this stage the cell must translate the sequence of an
mRNA molecule into the amino acid sequence of a polypeptide.
Copy Figure 17.3 summarizing the differences between transcription and translation in
prokaryotic and eukaryotic cells.
In Eukaryotes, the RNA is undergoes ________________ to yield the finished RNA.
The initial RNA transcript is called the ______________ _____________________.
p. 328
The Genetic Code
The flow of genetic information from gene to protein is based a __________ code. In
other words, codons of consisting of ____ bases specify one amino acid.
DNA strand that is transcribed is called the _________________ strand. An mRNA is
_____________________ rather than identical to the DNA template.
mRNA base triplets are called ___________.
Copy Figure 17.4
Bottom of p. 330: There is redundancy in the genetic code, but no _______________.
Top of p. 331: In order to interpreted correctly the symbols must read in the correct
______________ ________________.
Evolution of the Genetic Code p. 331
The genetic code is nearly ________________________, shared by organisms from the
simplest bacteria to the most complex plants and animals.
17.2 Transcription is the DNA-directed synthesis of RNA, p. 331
mRNA is transcribed from the template strand of the gene by the enzyme ______
________________________. (p. 332) RNA polymerases can only assemble a
polynucleotide in the _____ to ______ direction. Since RNA polymerases are able to
start a strand from scratch they do not need a primer.
Specific _____________ of nucleotides along the DNA mark where transcription of a
gene _________ and ______.
The region of DNA where RNA polymerase attaches and initiates transcription is known
as the _____________________. In bacteria, the sequence that signals the end of
transcription is called the ____________________.
Molecular biologists refer to the direction of transcription as “ ___________________”
and the other direction as “upstream”.
Synthesis of an RNA Transcript
The three stages of transcription are
______________________,_______________________ and ____________________.
Using Fig. 17.7, briefly describe each stage.
RNA Polymerase Binding and Initiation of Transcription
The promoter of the a gene includes within it the transcription ____________
__________ (the nucleotides where RNA synthesis actually begins) and typically extends
several dozen nucleotides upstream from the start point. In addition to serving as a
binding site for ________ __________________ and determining where transcription
______________, the promoter determines which of the two strands of the DNA helix is
used as the _____________________.
In prokaryotes the RNA _______________ itself specifically recognizes and binds to the
promoter.
In eukaryotes, by contrast a collection of specific collection of proteins called
__________________________ ________________ mediate the binding of RNA
polymerase and the initiation of transcription.
Only after certain transcription factors are attached to the promoter does RNA
polymerase II bind to it. The whole complex of transcription factors and RNA
polymerase II bound to the promoter is called the ______________________
______________________ complex.
Copy Figure 17.8
Elongation of the RNA Strand p. 333
As RNA polymerase moves along the DNA, it continues to untwist the double helix,
exposing 10 to 20 DNA bases at a time for pairing with RNA molecules. The enzyme
adds nucleotides to the ______ end of the growing RNA molecule.
Termination of Transcription, p. 333
The mechanism of termination differs between bacteria and eukaryotes.
In bacteria, transcription procedes through a ______________________ sequence of
DNA. The transcribed (RNA) terminator sequence functions as a termination signal,
causing polymerase to _____________ from the DNA and ________________ the
transcript.
In eukaryotes, RNA polymerase II transcribes a sequence on the DNA called the
_____________________________ signal sequence, which codes for a polyadenylation
signal ( ___ ____ ____ _____ ____ ) in the pre mRNA. Then at a point about ____ to
____ nucleotides downstream from the AAUAAA signal, proteins associated with the
RNA transcript cut it free from the polymerase, _________________ the pre-mRNA.
17.3 p. 334: Eukaryotic cells modify RNA after transcription
Enzymes in the eukaryotic _______________ modify _____- ________ in specific ways
before genetic messages are dispatched to the cytoplasm.
RNA Processing
Alteration of mRNA ends:
Each end of a pre-mRNA molecule is modified in a particular way. The 5’ end, the end
made first during transcription is immediately capped of with a _______________ form
of a ____________ (G) nucleotide.
The other end of the RNA molecule, the 3’ end is also modified before the message exits
the nucleus.To the 3’ end an enzyme adds a _________ tail consisting of 50 to 250
_________________ nucleotides. The 5’ cap and poly-A tail seem to 3 important
functions:
1)
2)
3)
Split Genes and RNA splicing, p. 334
Eukaryotic genes have long stretches of noncoding segments called intervening
sequences or ______________. The coding regions are called _____________, because
they are expressed.
Introns are removed by an assembly of small nuclear RNA (snps) and proteins called a
________________________. The spliceosome interacts with the splice sites at the ends
of the intron.
Copy Figure 17.10
Copy Figure 17.11
p. 336 Ribozymes – RNA molecules can function as ________________.
The Functional and Evolutionary Importance of Introns, p. 336
One consequence of the presence of introns is that a ____________ gene can encode
more than one kind of ________________________.
Alternative RNA splicing – different segments of RNA are treated as ____________
Presence of introns in a gene may facilate the ____________________ of new and
potentially useful by ____________ shuffling. Exon shuffling could lead to new proteins
with novel combinations of functions.
17.4, p. 337 TRANSLATION IS THE RNA-DIRECTED SYNTHESIS OF A
POLYPEPTIDE
Molecular Components of Translation
The function of transfer RNA (tRNA) is to ____________ ___________ __________
from the cytoplasm’s amino acid pool to a ribosome.
Molecules of tRNA are not all identical. Differ in which amino acid is attached at one
end and in the _____________ attached at the other end. The anticodon is a nucleotide
_____________ which binds according to base pairing rules to the
____________________ ______________ on mRNA.
Sketch figure 17.13
The Structure and Function of Transfer RNA, p.337
Sketch Fig. 17.14 – Label the amino-acid attachment site and the anticodon site
Aminoacyl –tRNA Synthetases p. 338
The accurate translation of a genetic message requires two processes that involve
molecular recognition. First a t-RNA that binds to an mRNA ______- specifying a
particular ________ ______ must carry that amino acid and no other, to the ribosome.
The correct matching up of t- RNA and amino acid is carried out by a family of enzymes
called _______________________ - ______ ____________________>
Ribosomes, p. 339
Ribosomes facilitate the specific coupling of tRNA _____________ with mRNA
___________.
A ribosome if made up of two subunits: _______________ and ____________
Ribosomal subunits are constructed of ____________ and RNA called
_________________________.
Describe the Roles of the P, A and E sites
P site:
A site:
E site:
Draw figure 17.16- Anatomy of a ribosome
Draw figure 17.17- Initiation of translation, p. 340
Draw figure 17.18- The elongation cycle of translation, p. 341
Draw figure 17.19- Termination translation
p. 342 Polyribosome
A polyribosome is
From Polypeptide to Functional Protein
Chemical modification of protein by attachment of sugar, lipids, phosphate groups or
cleaving of amino acid groups or cleavage of the chain are all examples of
______________________________ modifications.
Signal peptides target some Eukaryotic polypeptides to specific destinations in the cell.
Polypeptides destined for the endomembrane system or for secretion are marked by a
____________ __________, which targets the protein to the endoplasmic reticulum(ER).
The signal peptide, a sequence of about _____ amino acids at or near the
______________ (
) end of the polypeptide is recognized as it emerges
from the ribosome by a protein-RNA complex called a _____________________________ _____________________ (SRP).
p. 344 Point mutations can affect protein structure and function
Mutations are
Point mutations are chemical changes in just ______ or a few base pairs in a single gene.
Types of Point Mutations
Substitutions A base-pair substitution is
Nonsense mutations are
Insertion and deletions are
A frame shift mutation is