AP Biology : Understand steps of replication

Study concepts, example questions & explanations for AP Biology

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Example Questions

Example Question #62 : Central Dogma

What is not true regarding the origin of replication?

Possible Answers:

It is the sequence in the genome where DNA replication begins

The origin of replication binds to initiator proteins

Replication can continue in either direction from the origin of replication

It is the location where primers are added

Correct answer:

It is the location where primers are added

Explanation:

The origin of replication is the sequence of DNA where replication is initiated. The origin of replication often has a high content of adenine and thymine nucleotides because they are only bound together by two hydrogen bonds, making the helix easier to open and unwind. There are multiple origins of replication on each chromosome in eukaryotes, while there is only one origin of replication in prokaryotes. The origin of replication binds to initiator proteins that make up the pre-replication complex, which initiates replication.

Example Question #31 : Understand Steps Of Replication

Which of the following statements regarding DNA replication is false?

Possible Answers:

DNA polymerase requires a template

DNA replicates in a semiconservative fashion

DNA replication of the lagging strand is continuous

DNA polymerase requires a primer

DNA polymerization occurs in the 5' to 3' direction

Correct answer:

DNA replication of the lagging strand is continuous

Explanation:

The only false statement is that DNA replication of the lagging strand is continuous. The leading strand features continuous replication while the lagging stand is initially made up of discontinuous Okazaki fragments, which are sealed later by ligase.

Example Question #33 : Understand Steps Of Replication

Which of the following is true of mutations?

Possible Answers:

A translocation has occurred if a deleted chromosomal fragment is removed and reattaches to its original chromosome in reverse orientation 

A deletion has occurred if a chromosomal fragment is removed and reattaches elsewhere 

A translocation has occurred if a chromosomal fragment is removed and reattaches to a nonhomologous chromosome 

An inversion has occurred if a deleted chromosomal fragment attaches to a sister chromatid

An inversion has occurred if a chromosomal fragment is removed and reattaches elsewhere

Correct answer:

A translocation has occurred if a chromosomal fragment is removed and reattaches to a nonhomologous chromosome 

Explanation:

There are four major types of mutations: deletions, duplications, inversions, and translocations. Deletions occurs when a chromosomal fragment is removed and not replaced. Duplications occur when a chromosomal fragment is aberrantly copied. Inversions occur when a chromosomal fragment reattaches to its original chromosome in reverse orientation. Translocations occur when a chromosomal fragment reattaches to a different part of the same chromosome, or a different chromosome altogether.

Example Question #65 : Central Dogma

Which of the following enzymes is responsible for unwinding the double-helix of DNA and separating the two strands for replication?

Possible Answers:

DNA Polymerase III

Helicase

SSB

Primase

DNA Polymerase I

Correct answer:

Helicase

Explanation:

Helicase is the enzyme responsible for breaking the helix and unwinding the DNA into two separate strands. This allows the polymerase enzyme to attach and start adding base pairs for replication. Primase is responsible for setting and synthesizing RNA primers for polymerase attachment.

Example Question #66 : Central Dogma

__________ histones increase genetic expression.

Possible Answers:

Methylated

Acetylated

Demethylated

None of these

Deacetylated

Correct answer:

Acetylated

Explanation:

Acetylation of histones helps increase genetic expression. Acetylation is the process of adding an acetyl group. Methylation is used by the cell to differentiate between the two DNA strands of a newly synthesized DNA. Essentially, the highly methylated strand is the original or parent strand. This is integral in proofreading the new DNA.

Example Question #71 : Central Dogma

Major histocompatibility molecules (MHC) are critical for the functioning of the immune system. These proteins are utilized allow for communication between the immune system and the cells. MHC I are utilized to show which cells are in fact part of the body and which are foreign. MHC II are utilized to show the immune system when there is an intruder.

MHC I molecules are derived from chromosome 6. On chromosome 6, there is a specific gene that encodes for the molecule. On the gene, there are 3 locus (A, B, C) which allows for variability in the binding site of the MHC I molecule. The MHC gene is co-dominance and therefore adds to its diversity. During development, the gene is transcribed into MHC I molecules. However, some of these are broken down and react with a particular MHC I molecule. The reaction allows for the MHC I molecule to surface onto the cellular membrane and to self-identify the protein for the cytotoxic T-cell.

After translation, MHC II molecules are transported to the endosome. When a pathogen binds to the proper MHC II binding site, these molecules are then presented to T-Helper cells. In comparison, MHC I molecules interact with endogenous antigens whereas MHC II molecules interact with exogenous antigens.

A cell was lysed and was blotted for proteins, From the blot, high level of MHC molecules were synthesized. Based on the finding, what can be concluded about the DNA structure at the moment?

I. Euchromatic 

II. Heterochromatic

III. Condensed

Possible Answers:

III only

II only

I only

II and III

I and III

Correct answer:

I only

Explanation:

From the lab result, transcription and translation had just occurred in order to create the MHC molecules. In order for transcription and translation to occur, the DNA must not have been condensed (euchromatic).

Example Question #37 : Understand Steps Of Replication

While exploring the nucleus of a testicular Leydig cell from a living male mouse, Dr. Rod noticed a very peculiar shading of the entire region within the nucleus. He notes the appearance as very light appearing with minimal areas of dense staining. Which of the following correctly defines the type of chromatin he has found?

Possible Answers:

Euchromatin - much less condensed and transcriptionally active

Heterochromatin - highly condensed and transcriptionally inactive 

None of these

Heterochromatin - much less condensed and transcriptionally active

Euchromatin - highly condensed and transcriptionally inactive

Correct answer:

Euchromatin - much less condensed and transcriptionally active

Explanation:

Euchromatin is a term used to describe an area within the DNA that is much less condensed and highly active transcriptionally. Typically, these areas are seen in highly active cells that are producing many proteins. On the contrary, Heterochromatin are areas that are much more condensed and much less transcriptionally active. On electron micrograph images, euchromatin areas are typically lighter stained vs heterochromatin areas are much more densely stained.

Example Question #71 : Central Dogma

What is the process in which the DNA molecule separates into two strands then produces two new complementary strands following the rules of base pairing.

Possible Answers:

Replication

Translation

Transcription

Reformation

Correct answer:

Replication

Explanation:

Replication is the process in which the DNA molecule produces two new complementary strands. Transcription produces a messenger RNA, and translation produces a chain of amino acids that become a protein.

Example Question #71 : Central Dogma

What is the primary enzyme involved in DNA replication?

Possible Answers:

DNA polymerase

ATP synthase

RNA polymerase

Transciptase

Correct answer:

DNA polymerase

Explanation:

DNA polymerase is the primary enzyme involved in DNA replication. It is responsible for adding nucleotides to the growing DNA chain in the 5' to 3' direction. This enzyme also has proofreading functionality, which allows it to remove nucleotides that are mispaired in the 3' to 5' direction and replace them with the correct nucleotide.

Example Question #72 : Central Dogma

What DNA fragment would complement 5’ ATCGGTCAAT 3’ ?

Possible Answers:

3’ TAGCCAGTTA 5’

5’ GCTAACTGGC 3’

3’ GCTAACTGGC 5’

5’ TAGCCAGTTA 3’

3’ ATCGGTCAAT 5’

Correct answer:

3’ TAGCCAGTTA 5’

Explanation:

The correct answer must complementary base pair with the fragment in the 3’ to 5’ direction because the strands run anti-parallel to each other. Only three of the given options that will run anti-parallel, but only one complements the DNA properly.

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