AP Biology Unit 7 Test Review – Protein Synthesis & Gene Regulation
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Structural and functional evidence supports the relatedness of all domains.
o Evidence of student learning is a demonstrated understanding of each of the following:
 DNA and RNA are carriers of genetic information through transcription, translation and
replication.
 Major features of the genetic code are shared by all modern living systems.
Timing and coordination of specific events are necessary for the normal development of an organism, and these
events are regulated by a variety of mechanisms.
o Observable cell differentiation results from the expression of genes for tissue specific proteins.
Induction of transcription factors during development results in sequential gene expression.
DNA and RNA molecules have structural similarities and differences that define function.
o Evidence of student learning is a demonstrated understanding of each of the following:
 Both have three components — sugar, phosphate and a nitrogenous base — which form
nucleotide units that are connected by covalent bonds to form a linear molecule with 3' and 5'
ends, with the nitrogenous bases perpendicular to the sugar-phosphate backbone.
 The basic structural differences include:
 DNA contains deoxyribose (RNA contains ribose).
 RNA contains uracil in lieu of thymine in DNA.
 DNA is usually double stranded, RNA is usually single stranded.
 The two DNA strands in double-stranded DNA are antiparallel in directionality.
 Both DNA and RNA exhibit specific nucleotide base pairing that is conserved through evolution:
adenine pairs with thymine or uracil (A-T or A-U) and cytosine pairs with guanine (C-G).
o Purines (G and A) have a double ring structure.
o Pyrimidines (C, T and U) have a single ring structure.
 The sequence of the RNA bases, together with the structure of the RNA molecule, determines
RNA function.
o mRNA carries information from the DNA to the ribosome.
o tRNA molecules bind specific amino acids and allow information in the mRNA to be
translated to a linear peptide sequence.
o rRNA molecules are functional building blocks of ribosomes.
o The role of RNAi includes regulation of gene expression at the level of mRNA
transcription.
Genetic information flows from a sequence of nucleotides in a gene to a sequence of amino acids in a protein.
o Evidence of student learning is a demonstrated understanding of each of the following:
 The enzyme RNA-polymerase reads the DNA molecule in the 3' to 5' direction and synthesizes
complementary mRNA molecules that determine the order of amino acids in the polypeptide.
 In eukaryotic cells the mRNA transcript undergoes a series of enzyme regulated modifications.
 To foster student understanding of this concept, instructors can choose an illustrative
example such as:
o Addition of a poly-A tail
o Addition of a GTP cap
o Excision of introns
o Translation of the mRNA occurs in the cytoplasm on the ribosome.
o In prokaryotic organisms, transcription is coupled to translation of the message. Translation involves
energy and many steps, including initiation, elongation and termination.
✘The details and names of the enzymes and factors involved in each of these steps are beyond the scope
of the course and the AP Exam.
o The salient features include:
 The mRNA interacts with the rRNA of the ribosome to initiate translation at the (start) codon.
 The sequence of nucleotides on the mRNA is read in triplets called codons.
 Each codon encodes a specific amino acid, which can be deduced by using a genetic code chart.
Many amino acids have more than one codon.
✘Memorization of the genetic code is beyond the scope of the course and the AP Exam.
 tRNA brings the correct amino acid to the correct place on the mRNA.
 The amino acid is transferred to the growing peptide chain.
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 The process continues along the mRNA until a “stop” codon is reached.
 The process terminates by release of the newly synthesized peptide/protein.
 Phenotypes are determined through protein activities.
Gene regulation results in differential gene expression, leading to cell specialization.
o Both DNA regulatory sequences, regulatory genes, and small regulatory RNAs are involved in gene
expression.
 Evidence of student learning is a demonstrated understanding of each of the following:
 Regulatory sequences are stretches of DNA that interact with regulatory proteins to
control transcription.
o To foster student understanding of this concept, instructors can choose an
illustrative example such as:
 Promoters
 Terminators
 Enhancers
o A regulatory gene is a sequence of DNA encoding a regulatory protein or RNA.
 Both positive and negative control mechanisms regulate gene expression in bacteria and viruses.
 Evidence of student learning is a demonstrated understanding of each of the following:
o The expression of specific genes can be turned on by the presence of an inducer.
o The expression of specific genes can be inhibited by the presence of a repressor.
o Inducers and repressors are small molecules that interact with regulatory proteins and/or regulatory
sequences.
o Regulatory proteins inhibit gene expression by binding to DNA and blocking transcription (negative
control).
o Regulatory proteins stimulate gene expression by binding to DNA and stimulating transcription (positive
control) or binding to repressors to inactivate repressor function.
o Certain genes are continuously expressed; that is, they are always turned “on,”e.g., the ribosomal genes.
o In eukaryotes, gene expression is complex and control involves regulatory genes, regulatory elements and
transcription factors that act in concert.
 Evidence of student learning is a demonstrated understanding of each of the following:
 Transcription factors bind to specific DNA sequences and/or other regulatory proteins.
 Some of these transcription factors are activators (increase expression), while others are
repressors (decrease expression).
 The combination of transcription factors binding to the regulatory regions at any one time
determines how much, if any, of the gene product will be produced.
 Gene regulation accounts for some of the phenotypic differences between organisms with
similar genes.
Practice Questions
1. Which of the following normally leads to the production of functional messenger RNA in eukaryotic cells?
(A) A decrease in the rate of ribosome synthesis
(B) The removal of portions of RNA known as intervening sequences (introns)
(C) A decrease in RNA polymerase activity
(D) The replication of new messenger RNA molecules from existing messenger RNA molecules
(E) The formation of peptide bonds between adjacent nucleotides
2.
Which of the following organisms contains a single promoter that controls and regulates a region containing a group of genes
for a specific function?
(A) Euglena, a unicellular eukaryote that can produce its own food by photosynthesis and can also consume food
heterotrophically by phagocytosis
(B) Chytridiomycota, a primitive, saprobic fungus that degrades chitin and keratin
(C) Spirogyra, a green alga found in freshwater areas
(D) Lactobacillus, a rod-shaped bacterium that converts lactose into lactic acid
3.
In the figure to the right, what process is shown and what is its function?
(A) RNA replication: to replicate RNA in RNA-based organisms through
polypeptides.
(B) Polypeptide synthesis: to produce polypeptides that act as functional
proteins.
(C) Protein synthesis: to produce proteins out of polypeptides.
(D) DNA replication: to replicate DNA in DNA base organisms through
polypeptides.
4.
Most cells use a complex system to create proteins from the
information coded by the DNA. This system involves two
parts, transcription and translation. Transcription is when an
mRNA strand is generated from a DNA template using basepairing rules. The mRNA is then translated into proteins with
the help of the ribosome (shown to the right) and aminoacyltRNAs. In the image above, which roles do the following sites
play in translation?
(A) A site accepts the tRNA that matches the next codon; P
site holds the amino acid chain that will bond with the
amino acid in the A site; E site is where tRNA is released
(B) A holds the amino acid chain that will bond with the
amino acid in the P site; P site accepts the tRNA that
matches the next codon; E site is where tRNA is released
(C) E site accepts the tRNA that matches the next codon; P site holds the amino acid chain that will bond with the amino
acid in the E site; A site is where tRNA is released
(D) A site where translation takes place; P site where the tRNA matches to the next codon; E site holds amino acid strand
until peptide bond is formed then the tRNA is released
5.
The image above shows gene expression in bacteria. What is the function of the white molecules, and how do they affect
protein production?
(A) The white objects are enzymes that attach themselves to the green molecule and force the green molecule to release the
operator to allow transcription to initiate via RNA polymerase.
(B) They are transcription factors sent to stimulate the production of a certain protein.
(C) The white objects induce a shape change in the green molecule, causing it to release the operator and allowing RNA
polymerase to bind the promoter and initiate trranscription.
(D) The white objects have no effect on protein production; they are merely by-products of the release of the operator.
6.
Using the above image, name and describe how the green molecule influences cell products and function.
(A) The molecule is a repressor that prevents the transcription of a certain gene in the absence of the white objects.
(B) The attachment of the green molecule, the repressor, to the blue strand stimulate the cell to produce less white objects.
(C) It is a terminator that sets a limit to how many RNA polymerase could bind to that certain area at a time. This limits the
expression of the gene.
(D) It is a terminator that controls how much of the gene is expressed by the amount of white objects surrounding it.