Download ap biology - BellaireAPBio

*
AP BIOLOGY
TRANSCRIPTION AND
TRANSLATION
Student Packet
AP* is a trademark of the College Entrance Examination Board. The College Entrance Examination Board was not
involved in the production of this material.
Pictures reprinted from Biology by Campbell & Reece, Benjamin Cummings, 2002, 6th edition. Permissions Pending.
®
Copyright © 2009 Laying the Foundation , Inc., Dallas, TX. All rights reserved. Visit: www.layingthefoundation.org
Transcription and Translation
Overview: Prokaryote vs. Eukaryote
ÆTranscription: synthesizing RNA from a DNA template.
ÆTranslation: synthesizing protein from RNA created in transcription.
Prokaryotes
ÆBoth transcription and translation take place in
the cytosol since prokaryotes do not contain nuclei.
Eukaryotes
ÆTranscription takes place in the nucleus while
translation takes place in the cytoplasm. This
compartmentalization of events allows for
additional control and modification of products
(RNA splicing for example).
Transcription: DNA to RNA
ÆPromoters signify the beginning of the sequence
to be transcribed; terminators or transcription stop
sights signify the end.
ÆRNA Polymerase is guided into place by
transcription factors as it latches onto and unzips
the appropriate segment of DNA creating a
transcription bubble.
ÆRNA Polymerase will then attach appropriate
nucleotides (A,U,G,C) creating a complementary
strand from one side of DNA until it reaches the
terminator.
ÆRNA Polymerase will transcribe both expressed
(exons) genetic material that codes for protein and
the intervening introns.
®
Copyright © 2009 Laying the Foundation , Inc., Dallas, TX. All rights reserved. Visit: www.layingthefoundation.org
Transcription and Translation
RNA Processing: Eukaryotes only
5’ CAP
This unique bonding arrangement added to the 5’
end of a pre-mRNA results in increased length of
survival time for the mRNA when the cap is
added…increased survival time means more
translated protein. The 5’ cap also acts to guide the
ribosome into place during translation.
Poly (A) Tail
This “many adenine” tail allows for the exit of
mRNA from the nucleus. Not all RNA is destined
to be transcribed in the cytoplasm (histone proteins,
etc.). It is thought that the Poly (A) tail is the
“secret handshake” that allows the RNA to pass by
proteins in the nuclear pore and out into the
cytoplasm for translation.
Alternative Splicing
Splicing mRNA exons together in different combinations to produce different proteins. Example: The
original sequence ABCD may be spliced into ABC, ABD, ACD, etc. Research suggests that nearly 60%
of all human DNA is expressed as alternatively spliced RNA. Alternative splicing is pervasive in the
creation of antibodies.
®
Copyright © 2009 Laying the Foundation , Inc., Dallas, TX. All rights reserved. Visit: www.layingthefoundation.org
Transcription and Translation
Translation: RNA to Protein
Translation
Initiation
ÆThe small subunit of the ribosome begins protein synthesis at a start codon (most always AUG) of
mRNA with the help of intitiation factors. This is usually the 1st AUG closes to the 5’ end. This is
important in insuring that the protein is read with the correct reading frame.
ÆThe appropriate tRNA carrying the amino acid methionine will pair its anticodon via hydrogen bonds
with the mRNA codon according to base pairing rules.
ÆOnce the initiation complex is formed, the large subunit of the ribosome attaches “on top” of the small
subunit.
Elongation
ÆThe ribosome moves (translocation) one codon at a time attaching complementary mRNA codons with
tRNA anticodons. Because anticodons are associated with specific amino acids, the appropriate amino
acids are in the appropriate order (assuming no mutation).
ÆBefore each tRNA is released by the ribosome, the amino acid is joined via peptide bond to the
growing chain of amino acids.
Termination
ÆElongation continues until 1 of 3 stop codons is reached. Stop codons do not code for an amino acid,
but instead “call for” the binding of release factors. Once release factors are bound the mRNA, ribosomal
subunits, etc. all disengage.
ÆThe string of amino acids (protein) will fold into the proper 3-dimensional shape with the aid of
chaperonin proteins.
®
Copyright © 2009 Laying the Foundation , Inc., Dallas, TX. All rights reserved. Visit: www.layingthefoundation.org
Transcription and Translation
Recycling of materials and dditional information about translation…
Recycling of materials
ÆThe mRNA will be degraded and the nucleotides used again in the next message.
ÆThe “used” tRNA that have left behind amino acids can also be “recharged” with their appropriate
amino acid and used again as well.
Æ Multiple ribosomes may read an mRNAstrand at a time. This is structure of mRNA bound by multiple
ribosomes is referred to as polyribosomes.
ÆThe genetic code is degenerate or redundant due to the fact that there are 64 possible mRNA codons
and only 20 coding amino acids (actually 22 aminos can be made). When observing the genetic code or
codon chart above it should be noted that the 3rd nucleotide in a codon is the least important in
determining the corresponding amino acid. This phenomenon is called the “wobble effect.”
Exporting protein from the cell
ÆProtein will be manufactured by ribosomes on the
rough endoplasmic reticulum (RER). From here the
protein will be injected into the RER for packaging.
ÆThe protein will then be transported to the Golgi
apparatus via vesicle for further modification (addition
of sugars, etc.).
ÆThe tagged protein will now travel to the cell
membrane, fuse with the cell membrane, and export the
protein via exocytosis.
®
Copyright © 2009 Laying the Foundation , Inc., Dallas, TX. All rights reserved. Visit: www.layingthefoundation.org
Transcription and Translation
Multiple Choice
Questions 1-4 refer to the following terms
(A) Transcription
(B) Translation
(C) Replication
(D) Transformation
(E) Binary fission
1. The process in which RNA is created from a DNA template
2. The process by which bacteria replicate
3. This process occurs in the S phase of the cell cycle.
4. This process in which mRNA is “read” to create protein
5. Which of the following mRNA transcripts would be created from the DNA represented below?
3’-TACCGATC-5’
(A) 3’-TACCGATC-5’
(B) 3’-AUGGCUAG-5’
(C) 5’-AUGGCUAG-3’
(D) 5’-TACCGATC-3’
(E) 5’-AUCCGUAC-3’
6. Which of the following best represents the order of the pathway that is taken during protein
synthesis?
(A) mRNAÆrRNAÆ DNAÆ tRNAÆ protein
(B) mRNAÆ DNAÆ tRNAÆ protein
(C) DNAÆ tRNAÆ mRNAÆ protein
(D) DNAÆ mRNAÆ rRNAÆ tRNAÆ protein
(E) ProteinÆ mRNAÆ DNA
7. Which of the following structures contain anticodons?
(A) DNA
(B) mRNA
(C) rRNA
(D) tRNA
(E) snRNA
®
Copyright © 2009 Laying the Foundation , Inc., Dallas, TX. All rights reserved. Visit: www.layingthefoundation.org
Transcription and Translation
8. How many amino acids are contained in a protein that is coded for by a strand of mRNA that is 60
nucleotides in length. Ignore stop signals.
(A) 20
(B) 30
(C) 60
(D) 120
(E) 180
9. Which of the following bond(s) is/are responsible for joining amino acids during translation?
I. ionic
II. ovalent
III. phosphodiester
IV. peptide
(A) I and II only
(B) I and IV only
(C) I, II, and III only
(D) II and III only
(E) II and IV only
10. Which of the following is responsible for transporting the genetic code out of the nuclear pores in
eukaryotes for translation?
(A) DNA
(B) mRNA
(C) rRNA
(D) snRNA
(E) tRNA
®
Copyright © 2009 Laying the Foundation , Inc., Dallas, TX. All rights reserved. Visit: www.layingthefoundation.org
Transcription and Translation
Free Response
1. Protein synthesis is one of the most fundamental cellular processes.
A. Explain the process by which mRNA coding for insulin is translated into protein in the cytosol of
a eukaryotic cell.
B. Once the insulin has been manufactured, it must be shipped out of the cell. Describe all pertinent
processes and structures involved in this event.
2. DNA must first be transcribed into RNA language before translation to protein can occur.
A. Beginning with a strand of DNA in the nucleus, thoroughly describe the events of transcription.
B. Using the genetic code (“codon table”) to the
right:
i.
Determine the mRNA sequence and
the amino acids coded for by the
following DNA template
3’-TACGGGGTTGGAACT-5’
ii.
Explain the meaning of the statement
“the genetic code is redundant” and
discuss the significance of this
phenomenon.
®
Copyright © 2009 Laying the Foundation , Inc., Dallas, TX. All rights reserved. Visit: www.layingthefoundation.org