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Chapter 14 Protein Synthesis
Go to:
http://www.accessexcellence.org/AB/GG/#Anchor-Chromosomes-23240
Go through the various sites and review DNA synthesis
Go to: http://www.accessexcellence.org/AB/GG/protein_synthesis.html
Know the genetic code for the synthesis of polypeptides.
Go to: http://molbio.info.nih.gov/molbio/gcode.html
Be able to decode table for the synthesis of polypeptides.
http://molbio.info.nih.gov/molbio/gcode.html
Be able to do these questions without looking up the answers.
Go to: http://www.pathology.washington.edu/galleries/Cytogallery/
The University of Washington provide information on various chromosomal abnormalities.
Check it out.
http://photoscience.la.asu.edu/photosyn/courses/BIO_343/lecture/DNA-RNA.html
Rather technical but if you are going into bio-chemistry you may try following this site through
This last web site is the genetic code which you can also find in text book.
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Chapter 14
Protein Synthesis
I. What is the role of proteins in a cellular system
A. Proteins are used for maintenance, growth and development
II. How are proteins made : TRANSCRIPTION and
TRANSLATION
A. DNA
1. Instructions are coded in nucleotides consisting of :
A - adenine
T - thymine
G - guanine
C - cytosine
2. Twisted double stranded DNA bases pair in :
A-T;
C-G
3. In DNA replication base pairs unwind to serve as templates
assembly of new complementary strand
4. Gene - a linear stretch of DNA nucleotide sequence
a. Coding for an assembly of amino acids that forms a polypeptide chain
5. The path for gene expression has two steps :
a. Transcription - mRNA strand coded from DNA strand in a 5´ - 3´ direction
b. Translation - mRNA moved from nucleus to cytoplasm proteins are synthesized
in the ribosome
B. Three kinds of RNA play a part in protein synthesis
1. mRNA :
Single strand of information coded from DNA
2. rRNA :
Ribosome RNA functions as a catalytic site for acid assembly into a protein
3. tRNA :
Transfer RNA which bring the correct amino acid to the ribosome
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III. TRANSCRIPTION OF DNA TO RNA
A. RNA assembly
1. Three ways RNA differs from DNA (a comparison and contrast)
a. RNA is single strand
DNA is double strand
b. RNA uses Uracil
DNA uses Thymine
c. RNA uses ribose sugar
DNA uses deoxyribose sugar
B. RNA transcription differs from DNA replication
a. A single strand of RNA is synthesized from DNA
b. RNA polymerase catalyzes the synthesis of mRNA
1. DNA replication uses DNA polymerase
c. mRNA uses single region of a single strand of DNA is as a template
C. Final modification to mRNA
1. New mRNA not ready to use
2. mRNA is modified prior to export from nucleus
a. The 5´ end of mRNA is capped with a “start” signal for translation
b. A “poly-A tail” is added to the 3´ end of the mRNA
c. Non-coding portions (introns) are snipped out of mRNA
Coding regions (exxons) are spliced together.
IV. mRNA to PROTEINS
A. Genetic code
1.
Every three base pairs (triplets) of mRNA specifies an amino acid to be included in a
growing polypeptide chain
a. mRNA bases pairs are referred to as CODONS
b. 61 base pairs code for 20 amino acids and 3 base pairs serve
to stop protein synthesis : (UAA, UAG, UGA)
c. AUG (specifies methionine) is the “start” codon
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B. The roles of tRNA & mRNA in protein synthesis
1. Each of the 20 amino acids must attach to a specific tRNA
a. Each tRNA has specific triplet base pair (ANTI-CODON)
specific for the mRNA triplet base pair
2. After mRNA arrives in cytoplasm an anticodon of tRNA binds to the correct codon
sequence of the mRNA
a. The first two base pairs of anticodon must pair with the codon
by the rules of
A with U
&
G with C
b. The third base pair has some latitude in pairing resulting in condition of
WOBBLE effect
c. Transcription takes place within a ribosome structure
1) The ribosome is composed of rRNA and proteins which work together during
protein synthesis
C. STAGES OF TRANSLATION
1. (1) Initiation; (2) Elongation; (3) Termination
2. Initiation
a. A complex is formed between tRNA the small ribosomal
subunit, mRNA and the large ribosomal subunit
1) Initiation step begins with initiator tRNA (a tRNA
containing methionine amino acid)
2) Initiator tRNA binds to ‘P’ site of small ribosomal subunit
3) Scanning of mRNA allows recognition of codon AUG
4) Large ribosomal subunit binds to small ribosomal subunit
5) Specific tRNA for mRNA (anticodon to codon) binds to
‘A’ site of small ribosomal subunit
6) Reaction catalyzed between amino and carboxyl group
resulting in peptide bond
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3. Elongation
a. A series of tRNAs delivers amino acids in sequence by codon anti-codon
matching forming peptide bonds
4. Termination
a. Stop codon reached
b. Polypeptide chain is released into cytoplasm
5. Several ribosomes (POLYSOME) may be moving along the same mRNA simultaneously
V. MUTATION AND PROTEIN SYNTHESIS
A. Changes in the genetic struction of DNA
1. Changes in the protein structure should result
B. Gene mutation results from:
1. Bases being added, deleted, or replaced
2. Mutations are rare and may result from mutagens such as:
a. Viruses, ultraviolet light (UV), & chemicals
3. Spontaneous mutations
a. Sickle-cell anemia (single base-pair substituition)
b. DNA template frameshift
c. Transposable elements of DNA “jumping” to a new location on the DNA
Biology 101 Chapter 14
Name: _____________________________
Fill-in-the-Blanks
Which base follows the next in a strand of DNA is referred to. as the base (1) _____________. The region
of DNA that calls for the assembly of specific amino acids into a polypeptide chain is a
(2) ______________ . The two steps from genes to proteins are called (3) ______________ and
(4) ______________ . . In eukaryotes, during (5) _____________ , single-stranded molecules of RNA are
assembled on DNA templates in the nucleus. During (6)_____________________, the RNA molecules
are shipped from the nucleus into the cytoplasm, where they are used as templates for assembling (7)
___________________chains. Following translation, one or more chains become (8)________________
into the three-dimensional shape of protein molecules. Proteins have
(9)_________________________and (10)_____________________ roles in cells, including
control of DNA.
Complete the Table
Three types of RNA are transcribed from DNA in the nucleus (from genes that code only for RNA).
Complete the following table, which summarizes information about these molecules.
RNA Molecule
a. Ribosomal RNA
b. Messenger RNA
c. Transfer RNA
Abbreviation
Description/Function
Sequence
Arrange the steps of transcription in correct chronological sequence. Write the letter of the first step next to 15, the letter
of the second step next to 16, and so on.
15. ____________A. The RNA strand grows along exposed bases until RNA polymerase meets a
DNA base sequence that signals "stop."
16. ___________ B. RNA polymerase binds with the DNA promoter region to open up a local region
of the DNA double helix.
7._________ C. An RNA polymerase enzyme locates the DNA bases of the promoter region of one DNA
strand by recognizing DNA-associated proteins near a promoter.
18. _________ D. RNA is released from the DNA template as a free, single-stranded transcript.
19. _________ E. RNA polymerase moves stepwise along exposed nucleotides of one DNA strand;
as it moves. the DNA double helix keeps unwinding.
Com pletion
20. Suppose the line below represents the DNA strand that will act as a template for the production of
mRNA through the process of transcription. Fill in the blanks below the DNA strand with the sequence of
complementary bases that will represent the message carried from DNA to the ribosome in the cytoplasm.
(Transcribe single-strand of mRNA)
Matching
1. _____
2. _____
3. _____
4. _____
5. _____
6. _____
7. _____
8. _____
codon
three at a time
sixty-one
the genetic code
release factors
ribosome
anticodon
the "stop" codons
A. Composed of two subunits, the small subunit with P and A
amino acid binding sites as well as a binding site for
mRNA
B. Reading frame of the nucleotide bases in mRNA
C. Detach protein and mRNA from the ribosome
D. UAA, UAG, UGA
E. A sequence of three nucleotide bases that can pair with
a specific mRNA codon
F. Name for each base triplet in mRNA
G. The number of codons that actually specify amino acids
H. Term for how the nucleotide sequences of DNA and then
mRNA correspond to the amino acid sequence of a
polypeptide chain
Complete the Table
9. Complete the following table, which distinguishes the stages of translation.
Translation Stage
Description
Special initiator tRNA loads onto small ribosomal subunit and
recognizes AUG; small subunit binds with mRNA, and large ribosomal
subunit joins small one.
a.
Amino acids are strung together in sequence dictated by mRNA
codons as the
RNA strand passes through the two ribosomal subunits; two tRNAs
interact at P and A sites
b.
c.
mRNA "stop" codon signals the end of the polypeptide chain; release
factors detach the ribosome and polypeptide chain from the mRNA.
Completion
10. Given the following DNA sequence, deduce the composition of the mRNA transcript:
TAC AAG ATA ACA TTA
TTT
CCT
ACC GTC ATC
___
____
___
___
___
___
___
(mRNA transcript)
___
___
____
11. Deduce the composition of the tRNA anticodons that would pair with the above specific mRNA
codons as these tRNAs deliver the amino acids (identified below) to the P and A binding sites of the small
ribosomal subunit.
___
____
___
___
___
___
___
___
___
____
(tRNA anticondons)
From the mRNA transcript, use the text to deduce the composition of the amino acids of the
polypeptide sequence.
___
____
___
___
___
___
(amino acids)
___
___
___
____
Fill-in-the-Blanks
The order of (13)_______________
____________ in a protein is specified by a sequence of nucleotide
bases. The genetic code is read in units of (14) ______________ nucleotides; each unit of three codes for
(15) _______________ amino acids). In the table that showed which triplet specified a particular amino
acid, the triplet code was incorporated in (16) _________________molecules. Each of these triplets is
referred to as a(n) (17) __________________ (18) ________________ alone carries the instructions for
assembling a particular sequence of amino acids from the DNA to the ribosomes in the cytoplasm, where
(19) _____________________ of the polypeptide occurs. (20) ____________RNA acts as a shuttle
molecule as each type brings its particular (21) ______________________ to the ribosome where it is to
be incorporated into the growing (22)__________________________ . A(n) (23) is a triplet on mRNA
that forms hydrogen bonds with a(n) (24) __________________________ , which is a triplet on tRNA.
Fill-in-the-Blanks
In addition to changes in chrom osom es (crossing over, recom bination, deletion, addition. translocation.
and inversion), changes can also occur in the structure of DNA; these m odifications are referred to as
gene m utations. Com plete the following exercise on types of spontaneous gene m utations.
Viruses, ultraviolet radiation, and certain chemicals are examples of environmental agents called
(2) ______________
that may enter cells and damage strands of DNA. If A becomes paired
with C instead of T during DNA replication. this spontaneous mutation is a base-pair
(3)__________________. Sickle-cell anemia is a genetic disease whose cause has been traced to a single
DNA base pair; the result is that one (4) ___________ is substituted for another in the beta chain of
(5)__________________. A(n) (6)______________________ mutation is defined as the insertion or
deletion of one to several DNA base pairs; this puts the nucleotide sequence out of phase. and abnormal
proteins are produced. Some DNA regions "jump" to new DNA locations and often inactivate the genes
in their new environment; such (7) _____________________ elements may give rise to observable
changes in the phenotype of an organism. (8) _______________ is the source of the unity of life; (9)
_____________are the original source of life's diversity; they are heritable, small-scale alterations in the
(10) ___________________________ sequence of DNA. Each gene has a characteristic
(11)___________________________, which is the probability it will mutate spontaneously during a
given interval of time. But not all mutations are spontaneous. (12) ___________________________
radiation causes base substitutions or breaks in. one or both strands.
Self Quiz
1. Transcription __________________
a. occurs on the surface of the ribosome
b. is the final process in the assembly of a
protein
c. occurs during the synthesis of any type of
RNA by use of a DNA template
d. is catalyzed by DNA polymerase
2. ________________carry(ies) amino acids
to ribosomes, where amino adds are linked into the
primary structure of a polypeptide.
a. mRNA b. tRNA c. Introns d. rRNA
3. Transfer RNA differs from other types of RNA
because it
a. transfers genetic instructions from cell nucleus
to cytoplasm
b. specifies the amino acid sequence of a
particular protein
c. carries an amino add at one end
d. contains codons
4.dominates the process of
transcription.
a. RNA polymerase b. DNA polymerase
c. Phenylketonuria d. Transfer RNA
5. ______________and, __________ are found in RNA
but not in DNA.
a. Deoxyribose; thymine
b. Deoxyribose; uracil
c. Uracil; ribose
d. Thymine; ribose
6. If each kind of nucleotide is coded to select only one
amino acid, how many different types of amino acids
could be selected?
a. four
b. sixteen c. twenty d. Sixty-four
7. Each "word" in the mRNA language
consists of _________ letters.
a. three b. four c. five d. more than five
8. The genetic code is composed of codons.
a. three b. twenty c. sixteen d. sixty-four
9. The cause of sickle-cell anemia has been traced a. to
mosquito-transmitted virus
b. two DNA mutations that result in two incorrect
amino acids in a hemoglobin
chain
c. three DNA mutations that result in three
incorrect amino acids in a hemoglobin
chain
d. one DNA mutation that results in one
incorrect amino acid in a hemoglobin chain
10. An example of a mutagen is
a. virus
b. ultraviolet radiation
c. certain chemicals
d. all of the above