AP Biology Exam Review Unit 6

3. What is the function of mRNA?

carries genetic message from DNA to the ribosome (DNA can't leave nucleus, mRNA can)

8. How can a mutation have a negative effect on the product produced?

cause proteins to not form correctly, proteins can't function in the same way, causing genetic disorders or cancer

a. Detrimental?

cause proteins to not form correctly, proteins can't function in the same way, causing genetic disorders or cancer

16. What is the function of RNA splicing?

cutting out the introns (non-coding) with spliceosomes and splicing the exons (coding) back together to prepare for translation

3. What are the three steps of translation?

initiation, elongation, and termination

10. What is a codon?

smallest unit of uniform length that can code for all the amino acids

10. True or False: All somatic cells have the same DNA.

true

b. What happens when tryptophan is absent?

tryptophan absent, repressor inactive, operon on

a. What happens when tryptophan is present?

tryptophan present, repressor active, operon off

17. How does a virus incorporate its viral genome into a host genome?

using an enzyme called integrase

18. How do viruses form progeny viruses?

using the host cell's machinery the viral DNA will be transcribed and translated into viral proteins that will then be assembled with the copies of the viral genetic material.

3. How do mutations affect gene products?

can introduce new alleles which increase genetic variety = proteins changes

c. Is this operon repressible or inducible?

inducible

Where does translation take place?

at a ribosome either in the cytosol or at the endoplasmic reticulum

17. How does the repressor interact with the promoter?

A repressor is a protein that turns off the expression of one or more genes. The repressor protein works by binding to the gene's promoter region, preventing the production of messenger RNA (mRNA).

a. How many nucleotides make up a codon?

3

9. Which strand is the template strand?

3' → 5'

a. Which direction is the template strand READ?

3' → 5'

11. Which direction does transcription take place (which direction is the RNA synthesized)?

5' → 3'

14. What is the function of the poly-A tail?

50- 250 adenines added to the 3' end, facilitating the export of the mRNA from the nucleus, protect the strand from degradation from the hydrolytic enzymes, and

b. What codons code for lysine?

AAA, AAG

7. How is DNA modified to inhibit transcription (to regulate gene expression)?

DNA methylation, methyl groups are added to DNA which tightly packs it to reduce transcription; repressor transcription factors bind to the promoter to block RNA polymerase from attaching to the DNA

2. What is the promoter region?

DNA sequences that define where transcription of a gene by RNA polymerase begins

2. What is the central dogma?

DNA to RNA to Protein

15. What is the central dogma?

DNA → RNA → Protein

12. Why can different phenotypes result from different levels of gene expression?

Different tissues will express different genes based on which activators/transcription factors are present in those cell types. Alternative splicing in different cell types can also result in different genes being

Identify two examples of retroviruses.

HIV, SIV (simian) and human T-cell lymphotropic virus type 1 (HTLV-1) causes a form of cancer called adult T-cell leukemia (ATL)

8. How are histones modified to initiate transcription (to regulate gene expression)?

Histone acetylation, removes the positive charge on the histones, and the condensed chromatin is transformed into a more relaxed structure

9. How are histone modified to inhibit transcription (to regulate gene expression)?

Histone deacetylation, removes the negative charge on the histones, DNA becomes more tightly wrapped around the histones, making it harder for transcription factors to bind to the DNA

8. What chemical process releases the growing polypeptide?

Hydrolysis the release factors cause the ribosome peptidyl transferase to add a water molecule to the carboxyl end of the most recently added amino acid in the growing polypeptide chain attached to the P-site tRNA. This causes the polypeptide chain to detach from its tRNA, and the newly-made polypeptide is released.

5. What is the function of rRNA?

It physically moves along an mRNA molecule and catalyzes the assembly of amino acids into protein chains. They also bind tRNAs and various accessory molecules necessary for protein synthesis

6. How does the mRNA, tRNA, and rRNA all interact?

Messenger RNA (mRNA) carries the genetic information copied from DNA to the cytoplasm Transfer RNA (tRNA) is the key to deciphering the codons in mRNA. Each type of amino acid has its own type of tRNA, which binds it and carries it to the growing end of a polypeptide chain. The correct tRNA with its attached amino acid is selected at each step because each specific tRNA molecule contains a three-base sequence (anticodon) that can base-pair with its complementary codon in the mRNA. Ribosomal RNA (rRNA) associates with a set of proteins to form ribosomes. These complex structures, which physically move along an mRNA molecule, catalyze the assembly of amino acids into protein chains. They also bind tRNAs and various accessory molecules necessary for protein synthesis. Ribosomes are composed of a large and small subunit, each of which contains its own rRNA molecule or molecules.

What is transcription?

Transcription is the process of taking a DNA sequence and copy it into a message that can then be sent out to the ribosomes to carry the message to build a protein.

What amino acid is coded by UAU?

Tyrosine

5. What happens if an insertion or deletion occurs at a nucleotide base pair?

can cause a frameshift

3. What is the TATA box?

a DNA sequence that indicates where a genetic sequence can be read and decoded. It is a type of promoter sequence, which specifies to other molecules where transcription begins

15. What is a repressor?

a DNA- or RNA-binding protein that inhibits the expression of one or more genes by binding to the operator or associated silencers

19. Describe the trp operon.

a repressible operon, transcription is usually on, but can be inhibited whentryptophan binds allosterically to the regulatory protein

What is an operon?

a sequence of DNA containing a cluster of genes under the control of a single promoter

16. What is a promoter?

a sequence of DNA to which proteins bind that initiate transcription of a single RNA from the DNA downstream of it. This RNA may encode a protein, or can have a function in and of itself, such as tRNA, mRNA, or rRNA

nucleus.

a. 5' cap is added to the 5' end to protect it from exonucleuses which target 5' ends b. a polyA tail is added to the 3' end of the RNA molecule to help the RNA molecule leave the nucleus and to protect it from exonucleases c. noncoding introns are removed from the RNA strand and the exons are spliced together

12. Describe the process that takes place during transcription.

a. initiation - RNA polymerase binds to the promoter sequence of DNA and then separates the DNA strands of the specific gene it is trying to transcribe. b. elongation - the template strand of DNA acts as the template for RNA polymerase. RNA polymerase "reads" the template strand one base at a time and will add the complementary RNA nucleotides making a chain that grows from 5' to 3'. c. termination - terminator sequences signal that the RNA transcript is complete. an example of a

6. How is DNA modified to initiate transcription (to regulate gene expression)?

activator transcription factors attach to the promoter and recruit RNA polymerase to increase transcription

14. How does the genetic code demonstrate common ancestry?

all living organisms store their genetic information using the same nucleotide bases

a. How does this affect the protein product?

all nucleotides downstream will be improperly grouped into codons, affecting protein production

17. How can multiple proteins be synthesized from the same mRNA transcript?

alternative RNA splicing

6. What happens in the elongation step of translation?

amino acids are brought to the ribosome by tRNAs and linked together to form a chain, the methionine-carrying tRNA starts out in the middle slot of the ribosome, called the P site. Next to it, a fresh codon is exposed in another slot, called the A site. The A site will be the "landing site" for the next tRNA, one whose anticodon is a perfect (complementary)

16. What is the function of reverse transcriptase?

an enzyme that catalyzes the formation of DNA from an RNA template

18. Describe the lac operon.

an inducible operon (usually off, but can be induced when lactose interacts with a regulatory protein

7. How can differential gene expression affect the cellular products?

depending on the cell type there can be different activators available to control which genes are expressed in which tissues; this will cause specific products to be produced only in specific tissues (example: albumin gene is expressed in liver cells, but not in lens cells)

8. How can differential gene expression affect the cellular functions?

depending on which genes are expressed in which tissues, specific proteins will be made leading to more specific cellular functions

9. What is siRNA?

double stranded siRNA (small interfering RNA) is able to regulate the expression of genes, by RNAi (RNA interference)

4. What are the three sites found on a ribosome and what is their function?

e site (exit site) - discharges the tRNA p site (peptidyl- tRNA binding site) - holds the tRNA carrying the polypeptide a site (aminoacyl-tRNA binding site) - holds the tRNA carrying the next amino acid to be added to the polypeptide chain

13. True or False: One codon can code for more than one amino acid.

false

6. How can a mutation have a neutral effect on the product produced?

if they don't change the amino acid sequence, and it doesn't change the protein coding

c. Neutral?

if they don't change the amino acid sequence, and it doesn't change the protein coding

10. What is involved in the cell's DNA repair mechanisms?

mismatch repair: direct reversal of the damage,base or nucleotide excision repair, and postreplication repair

b. How does this affect the amount of the protein product?

missense mutations caused by the frameshift will cause nonsense mutation and a premature termination - protein will be (mostly) non-functional

15. What is the function of the GTP cap?

modified cap of 20-40 guanines added to the 5' end, this helps ribosomes attach to the 5' end once the mRNA reaches the cytoplasm

5. What are epigenetic changes?

modify the activation of certain genes, but not the genetic code sequence of DNA

12. What is the cause of new genetic variation?

mutations

2. How do new phenotypes originate?

mutations, horizontal gene transfer, recombination/ crossing over

What causes errors in DNA replication?

mutations, insertions/deletions

7. How can a mutation have a positive effect on the product produced?

new versions of proteins that are evolutionarily beneficial

b. Beneficial?

new versions of proteins that are evolutionarily beneficial

10. What are the other names of the template strand?

noncoding strand, antisense strand

14. Identify an error in meiosis that leads to a change in phenotype.

nondisjunction

13. Identify an error in mitosis that leads to a change in phenotype.

nondisjunction can cause cancer

3. How do transcription factors affect the binding at the promoter?

only after the transcription factors are attached to the promoter does RNA polyII attach to it

How does the genotype influence the phenotype?

phenotype expression is the physical reflection of the possible gene combination

a. How does the location of translation affect gene expression in a prokaryote?

prokaryotes can perform both transcription and translation simultaneously

2. How does the location of translation differ between a prokaryote and a eukaryote?

prokaryotes onlyhave free floating ribosomes; whereas eukaryotes have either free floating or bound ribosomes

12. How are multiple codons able to code for the same amino acids?

redundancy, not ambiguity

4. What is the enhancer region?

regulatory DNA sequences that, when bound by specific proteins called transcription factors, enhance the transcription of an associated gene

c. Is this operon repressible or inducible?

repressibleWhat is the function of the promoter? to initiate transcription (it's where the RNA polymerase attaches to on the DNA sequence)

b. What happens when lactose is absent?

repressor active, operon off /glucose present, cAMP level low, little lac mRNA synthesized

a. What happens when lactose is present?

repressor inactive, operon on /glucose scarce, cAMP level high, abundant lac mRNA synthesized

5. How do negative regulatory molecules inhibit gene expression?

repressor protein binds to an operator to prevent a gene from being expressed

9. Where does translation start?

ribosome (30s subunit)

What are regulatory sequences?

segment of a nucleic acid molecule which is capable of increasing or decreasing the expression of specific genes within an organism

What is the function of RNA polymerase?

separates the DNA strands and joins the complementary RNA nucleotides to the DNA template strand

11. How do siRNA and miRNA affect gene expression?

siMRAs inhibit the expression of one specific target mRNA, while miRNA's regulate the expression of multiple mRNAs

4. What are the three types of substitution point mutations?

silent, missense, and nonsense

a. How does each affect the protein product?

silent: no change in amino acids, missense: substitute another amino acid, nonsense: early termination

b. How does each affect the amount of the protein product?

silent: no change, missense: can have no effect or render the protein nonfunctional, nonsense: protein shorter or unfinished

10. What is miRNA?

single-stranded miRNA (MicroRNA) are small, highly conserved non-coding RNA molecules involved in the regulation of gene expression by degrading their target mRNAs and/or inhibiting their translation.

What is differential gene expression?

the expression of different genes in cells with the same genome

What happens in the termination step of translation?

the finished polypeptide is released to go and do its job in the cell, termination happens when a stop codon in the mRNA (UAA, UAG, or UGA) enters the A site.

What is cell differentiation?

the process of specialization leading to the formation of brain, heart, and all other tissues from the single-cell zygote and the primitive, three-layered embryo

5. What happens in the initiation step of translation?

the ribosome gets together with the mRNA and the "initiator" tRNA, carrying the first amino acid in the protein, which is almost always methionine (Met)

13. What is the function of transcription factors?

to mediate the binding of RNA polymerase and the initiation of transcription

2. What is the function of transcription factors?

to mediate the binding of RNA polymerase and the initiation of transcription

4. What is the function of tRNA?

to read the mRNA and transfer the amino acids to the growing polypeptide

4. What is the function of RNA polymerase?

to separate the DNA strands and join the complementary RNA nucleotides to the template strand

a. How does a retrovirus violate this process?

transcribes DNA from RNA, use the enzyme reverse transcriptase.