All AP Biology Resources
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?
Cytoplasm
Smooth endoplasmic reticulum
Rough endoplasmic reticulum
Ribosome
Nucleus
Nucleus
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 __________.
replication
translation
transcription
transformation
transcription
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?
5'-TTACGCAT-3'
5'-AATGCGTA-3'
5'-UACGCAUU-3'
5'-AAUGCGUA-3'
5'-AUGCGUAA-3'
5'-AAUGCGUA-3'
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?
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
DNA ligase joins Okazaki fragments together
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 __________.
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
All of the answer choices are correct
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?
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'
5'-TGAACTGA-3'
5'-TCAGTTCA-3'
5'-AGUCAAGU-3'
5'-AGTCAAGT-3'
5'-AGTCAAGT-3'
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?
Prevent the separated strands from reannealing
Recruit DNA polymerase
Ensure both strands are replicated at similar rates
Synthesizing RNA primers
Prevent the separated strands from reannealing
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?
Restriction enzymes and DNA polymerase
DNA polymerase and topoisomerase
DNA polymerase and ligase
Restriction enzymes and topoisomerase
Restriction enzymes and ligase
Restriction enzymes and ligase
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?
Unwind the double-stranded DNA
Fix breaks in the sugar-phosphate backbone
Scan for mismatches
Add primers to the lagging strand
Unwind the double-stranded DNA
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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