Download File

Chapter 9B: Molecular Biology
9.3 Transcription
The Central Dogma
What is the central dogma?
Click in the boxes to type in the processes for each stage
DNA
RNA
Protein
Transcription: from DNA to mRNA
(RNA structure is discussed in section 9.1 of this chapter)
Initiation
What is a transcription bubble?
What structure do proteins and enzymes bind to initiate transcription?
Label the figure:
DNA
nontemplate
strand
Promoter
RNA
DNA
template
strand
Transcription
bubble
1
Elongation
Transcription always _______________ from one of the two DNA strands, which is called the _______________ strand.
The mRNA product is _______________ to the _______________ strand and is almost _______________ to the other
DNA strand, called the _______________ strand, with the exception that RNA contains a _______________ (U) in place
of the _______________ (T) found in DNA. During _______________, an enzyme called RNA _______________
proceeds along the DNA template adding _______________ by base _______________ with the DNA template in a
manner _______________ to DNA replication, with the _______________ that an RNA strand is being
_______________ that does not remain _______________ to the DNA template. As _______________ proceeds, the
DNA is _______________ unwound ahead of the core enzyme and _______________ behind it.
Termination
What is a termination signal?
“Transcribe” the following DNA sequence (follow base pairing rules A=U, T=A, G=C)
3’
CCGCTTAGCCTTAGCGATAAG5’
______________________________
Eukaryotic RNA Processing
Select the letters from this figure that best fit the descriptions below.
_____ Unit of transcription in a DNA strand
_____ Enzymes attach a modified guanine “cap”
that will bind the mRNA to a ribosome
_____Different enzymes attach a “poly-A tail” of
about 100-300 adenine riboncleotides
_____Introns, or gene sequences that are
removed before an mRNA is used for protein
synthesis
_____exons, coding parts of a gene sequence;
exons alternate with introns
_____ introns are snipped out before the mRNA leaves the nucleus in mature form; introns remain in the nucleus, where
they are recycled
_____Mature mRNA transcript
2
9.4 Translation
The Protein Synthesis Machinery and The Genetic Code
Match each term with its description
_____ codon
a.
large and small are assembled in the nucleus from rRNA and
proteins; shipped separately to the cytoplasm; intact and
functional when translation is to occur
_____three bases at a time
b.
reading frame of the nucleotide bases in mRNA
_____61 of the base triplets
c.
AUG
_____the genetic code
d.
UAA, UAG, UGA
_____ribosome subunits
e.
the set of 64 different codons
_____anticodon
f.
a sequence of three tRNA nucleotide bases that can pair with a
specific mRNA codon
_____the “stop” codons
g.
the number of mRNA base triplets that actually specify amino
acids
_____the “start” codon
h.
name for each base triplet in mRNA
Given the following DNA sequence what would the sequence of a mRNA transcript be following transcription (remember
complementary base pairing rules)
(the first codon is done as an example)
TAC AAG ATA ACA TTA TTT CCT ACC GTC ATC
AUG ___ ___ ___ ___ ___ ___ ___ ___ ___ (mRNA transcript)
For each of the following mRNA codons deduce the tRNA anticodons that would base pair (the first anti-codon is done
AUG CUU GGA UUC CAG
UTC ___ ___ ___ ___
(tRNA anticodons)
Use the genetic code in the text to deduce the sequence of the amino acids coded by the given mRNA (the first amino
acid is done) Each type of amino acid is abbreviated in the table in the text book. Use those three letter abreviations.
AUG CAA UGC GUC AAU CCA UCA GAU CUG UUA
met ___ ___ ___ ___ ___ ___ ___ ___ ___ (amino acids)
Write the RNA sequence for a start codon _________________
What amino acid is coded for by this sequence? ______________
Write one of the codons that would signal the end of translation
3
The Mechanism of Protein Synthesis
Label the initiation complex (labels to use: large ribosomal subunit, small ribosomal subunit, initiator tRNA, mRNA,
codon, anti-codon, and amino acid (methionine)). Click in the text box to type your answers.
Number the following steps in the correct chronological sequence
______A peptide bond forms between the first two amino acids
______ A fourth tRNA binds the fourth codon
______ The second tRNA is released and the ribosome moves to the next codon
______ The process repeats until the ribosome encounters a stop codon in the mRNA
______ Ribosome subunits and an initiator tRNA converge on an mRNA.
______ The first tRNA is released and the ribosome moves to the next codon
______ A second tRNA binds to the second codon
______A peptide bond forms between the second and third amino acids
______ A third tRNA binds to the third codon
______ A peptide bond forms between the third and fourth amino acids
4
9.5 How Genes Are Regulated
True-False: If the statement is true, type a T in the blank. If the statement is false, correct it by changing the underlined
word(s) and writing the correct word(s) in the answer blank.
_________ Only prokaryotic cells control when and how its genes are expressed
_________ Cells in different tissues look alike and perform the same functions
_________ Changes in the environment will result in certain genes being turned on or off.
_________ The control of gene expression is extremely simple.
_________ Transcription and translation occur almost simultaneously in prokaryotes.
_________ The primary method to control what type and how much protein is expressed in a eukaryotic cell is through
DNA transcription
_________ When lactose is present in a bacterium’s environment, the lac genes are transcribed in small amounts
_________ Eukaryotic cells control gene expression at all stages of the transcription and translation process.
5