AP Biology : AP Biology

Study concepts, example questions & explanations for AP Biology

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Example Questions

Example Question #25 : Understand Steps Of Transcription

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.

Based on the passage, where are MHC molecules transcribed? 

Possible Answers:

Cytoplasm 

Smooth endoplasmic reticulum

Rough endoplasmic reticulum

Ribosome

Nucleus 

Correct answer:

Nucleus 

Explanation:

From the passage, chromosome 6 carries the information for the MHC molecules. The chromosomes are stored in the nucleus of the cell. Therefore, transcription occurs in the nucleus. 

Example Question #2311 : Ap Biology

The process by which the genetic code of DNA is copied into a strand of messenger RNA is called __________.

Possible Answers:

replication

translation

transcription

transformation

Correct answer:

transcription

Explanation:

The process by which the genetic code of DNA is copied into a strand of messenger RNA is called transcription. Translation uses messenger RNA, transfer RNA, and ribosomal RNA to create a chain of amino acids that become a protein. Replication is the reproduction of two strands of DNA that are used in a new cell.

Example Question #2312 : Ap Biology

A DNA template is composed of the following nucleotide sequence:

5'-TACGCATT-3'

What is the mRNA transcript for this template?

Possible Answers:

5'-TTACGCAT-3'

5'-AATGCGTA-3'

5'-UACGCAUU-3'

5'-AAUGCGUA-3'

5'-AUGCGUAA-3'

Correct answer:

5'-AAUGCGUA-3'

Explanation:

When finding the mRNA transcript from a template, there are two things to keep in mind:

1. The template strand will be complementary to the transcript, so it will be read in the opposite direction

2. Since the template strand is made from DNA, it will have thymine bases instead of uracil (which is found in RNA in place of thymine).

First, we can reverse the direction of our given DNA sequence.

5'-TACGCATT-3'

3'-TTACGCAT-5'

Then, complete each base pair. Guanine (G) and cytosine (C) always pair, and adenine (A) and thymine (T) always pair. In this case, since we are dealing with RNA, uracil (U) will have an adenine complement.

5'-AAUGCGUA-3'

Example Question #1 : Understand Steps Of Replication

Which of the following represents a step necessary to create the lagging strand, but not the leading strand, during DNA replication?

Possible Answers:

Helicase unwinds the parent strand of DNA

DNA polymerase synthesizes template DNA from the parent strand

DNA ligase joins Okazaki fragments together

DNA is synthesized in the 5’ to 3’ direction

Correct answer:

DNA ligase joins Okazaki fragments together

Explanation:

Okazaki fragments are only produced, and subsequently joined together, in the lagging strand to allow for replication in the opposite direction as replication fork movement. The leading strand, however, allows for continual replication.

All other choices reflect aspects of DNA replication for both the leading and lagging strands.

Example Question #2 : Understand Steps Of Replication

Point mutations __________.

Possible Answers:

All of the answer choices are correct

include silent mutations, which have no effect on the organism's phenotype

include missense mutations, which only affect the codon in which the mutation occurs

include nonsense mutations, which change an amino acid to a stop codon, affecting the entire polypeptide structure

Correct answer:

All of the answer choices are correct

Explanation:

Point mutations replace a single nucleotide for a different one. This can change a certain codon to code for a different amino acid (missense), the same amino acid (silent), or lead to a stop codon (nonsense). Nonsense mutations are the most severe type of point mutation, as they will cause early termination of the protein.

Example Question #3 : Understand Steps Of Replication

How many copies of DNA would you have after ten replication cycles if you start with four copies?

Possible Answers:

Correct answer:

Explanation:

This is really just a math equation. We need to double the amount of DNA each time it goes through a replication cycle.

Begin: 4

Cycle 1: 8

Cycle 2: 16

Cycle 3: 32

Cycle 4: 64

Cycle 5: 128

Cycle 6: 256

Cycle 7: 512

Cycle 8: 1024

Cycle 9: 2048

Cycle 10: 4096

After ten cycles, we would have 4096 copies from our original 4.

A shortcut calculation would be .

This is why PCR amplification is so effective.

Example Question #3 : Understand Steps Of Replication

Select the complementary strand of DNA for the following DNA segment.

5'-ACTTGACT-3'

Possible Answers:

5'-TGAACTGA-3'

5'-TCAGTTCA-3'

5'-AGUCAAGU-3'

5'-AGTCAAGT-3'

Correct answer:

5'-AGTCAAGT-3'

Explanation:

The complementary strand will be going in the opposite direction (3'-5'). As a result, you will need to flip the direction in order for it to be complementary to the original strand. When pairing bases, remember that guanine (G) and cytosine (C) are paired with one another, and adenine (A) and thymine (T) are paired.

5'-ACTTGACT-3' Switch the direction.

3'-TCAGTTCA-5' Find the complement pairs.

5'-AGTCAAGT-3'

Example Question #4 : Understand Steps Of Replication

What is the function of the single-strand binding protein during DNA replication?

Possible Answers:

Prevent the separated strands from reannealing 

Recruit DNA polymerase

Ensure both strands are replicated at similar rates

Synthesizing RNA primers

Correct answer:

Prevent the separated strands from reannealing 

Explanation:

Single-strand binding protein (SSB) binds the newly separated DNA strands to ensure that it does not reanneal during replication. This keeps the strands separate so that replication can occur.

All of the other answers describe the functions of other proteins. Primase synthesizes the RNA primers, which helps to recruit DNA polymerase. The structural basis for the replication of the leading and lagging strands ensures that replication follows the same rate on both strands.

Example Question #5 : Understand Steps Of Replication

Which enzymes are necessary to produce recombinant DNA?

Possible Answers:

Restriction enzymes and DNA polymerase

DNA polymerase and topoisomerase

DNA polymerase and ligase

Restriction enzymes and topoisomerase

Restriction enzymes and ligase

Correct answer:

Restriction enzymes and ligase

Explanation:

Recombinant DNA technology involves combining genes from two sources, such as different species, into a single molecule.

Applying restriction enzymes to DNA will cleave the DNA into fragments, which can be isolated for specific genes. Ligase can then be used to fuse the fragments together into a full recombinant gene.

Topoisomerase is responsible for relieving tension in the winding of the DNA helix. DNA polymerase synthesizes new DNA from individual nucleotides, but would not be useful in fusing two types of DNA together.

Example Question #6 : Understand Steps Of Replication

What is the function of a helicase enzyme during DNA replication?

Possible Answers:

Unwind the double-stranded DNA

Fix breaks in the sugar-phosphate backbone

Scan for mismatches

Add primers to the lagging strand

Correct answer:

Unwind the double-stranded DNA

Explanation:

Helicases are enzymes that separate annealed strands of nucleic acids. This function provides the single-stranded template used in replication.

Primase is responsible for adding DNA primers, DNA polymerase I scans for mismatched nucleotides and mutations, and ligase repairs breaks in the DNA backbone.

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