AP Biology : Central dogma

Study concepts, example questions & explanations for AP Biology

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Example Questions

Example Question #5 : Understand Steps Of Transcription

The TATA box is bound by which of the following proteins?

Possible Answers:

Transcription factors

DNA polymerase III

RNA polymerase II

DNA polymerase I

RNA polymerase I

Correct answer:

Transcription factors

Explanation:

Transcription factors bind to the TATA box (found only in eukaryotes and archaea). The TATA box is a promoter region of a gene on the DNA. If the transcription factor that binds it is an activator, then it will interact with RNA polymerase II to form a transcription initiation complex and begin transcription of mRNA. DNA polymerases I and III are involved in DNA replication, and do not interact with the TATA box. RNA polymerase I is responsible for transcribing rRNA genes in the nucleolus.

Example Question #1 : Understand Steps Of Transcription

Which of the following are purines?

Possible Answers:

Cytosine only

Guanine only 

Adenine and guanine

Adenine only

Cytosine and guanine

Correct answer:

Adenine and guanine

Explanation:

To help remember which bases are purines and which are pyrimidines, there are two acronyms. Pure As Gold. Adenine and guanine are purines because of their structure. Also, pyrimidines, like pyramids, are "sharp". Sharp things CUT (cytosine, uracil and thymine).

Example Question #1 : Understand Steps Of Transcription

Which statement is true regarding DNA?

Possible Answers:

It is a single-stranded molecule

It is a protein

It contains adenine, guanine, cytosine, and thymine

It cannot be replicated

It contains adenine, guanine, cytosine, and uracil

Correct answer:

It contains adenine, guanine, cytosine, and thymine

Explanation:

DNA is a nucleic acid, made up of the nucleotides, which contain a deoxyribose sugar, a phosphate group, and one of four nitrogenous bases. These bases are adenine, cytosine, guanine, and thymine. DNA is double-stranded, but transiently single-stranded during DNA replication and transcription.

Example Question #11 : Central Dogma

What is the role of an activator?

Possible Answers:

Binds to RNA polymerase to initiate transcription 

Increases transcription of a specific gene

Decreases transcription of a specific gene

Activates transcription of the entire genome

Correct answer:

Increases transcription of a specific gene

Explanation:

Activators are proteins that increase transcription of a specific gene. Activators bind to promoters and often coactivators to facilitate binding of the pre-activation complex and initiation complexes; therefore, they stimulate the transcription of a given gene. 

Example Question #9 : Understand Steps Of Transcription

Where does RNA polymerase bind during transcription?

Possible Answers:

RNA polymerase binds to the sequence downstream of the promoter sequence.

RNA polymerase binds to the activators.

RNA polymerase binds to the promoter sequence within the DNA template.

RNA polymerase binds to the transcription factors. 

Correct answer:

RNA polymerase binds to the promoter sequence within the DNA template.

Explanation:

During transcription, RNA polymerase enzymes bind to DNA promoter sequences. This binding is facilitated by the pre-initiation complex (composed of transcription factors, the promoter sequence, activators, and repressors) as well as RNA polymerase. In eukaryotic cells, certain transcription factors must bind to the promoter sequence before RNA polymerase can. This is due to an inability of RNA polymerase to independently recognize the promoter sequence. Once RNA polymerase does bind, transcription can be initiated. 

Example Question #1 : Understand Steps Of Transcription

Which of the following proteins play a role in proofreading during transcription?

Possible Answers:

Transcription factors

Activators

RNA polymerase

RNA ligase

Correct answer:

RNA polymerase

Explanation:

Proofreading occurs during the elongation phase of transcription. RNA polymerase's movement over the DNA template strand includes a backtracking motion that allows RNA polymerase to proofread the newly synthesized RNA transcript.

Example Question #11 : Understand Steps Of Transcription

Which of the following is the central dogma of biology?

Possible Answers:

Correct answer:

Explanation:

The genetic information in a cell is stored in its DNA. Through transcription, the cell is able to create RNA from DNA. This RNA is called mRNA. The mRNA is then able to create protein through translation. Thus, the flow of information is from DNA to RNA to protein. 

Example Question #11 : Central Dogma

What type of chromatin would be found in telomeres and centromeres?

Possible Answers:

Both heterochromatin and euchromatin

Heterochromatin

Either heterochromatin or euchromatin, depending on the cell type

Euchromatin

Neither heterochromatin nor euchromatin

Correct answer:

Heterochromatin

Explanation:

Telomeres and centromeres are composed of heterochromatin. In contrast to euchromatin, heterochromatin's genes are generally in an inactive state. This is because the genetic material is highly condensed. Often, heterochromatin is thought of as "junk DNA". Since telomeres are slowly being degraded during DNA replication, the cell does not want to have active or important genes in this area. Same goes for centromeres, where there is the possibility of chromatids not separating evenly across the centromere in anaphase. 

Example Question #11 : Central Dogma

If a DNA template (the strand actively being transcribed) begins with AAGGCTCGGAA, what will the nascent RNA template begin with?

Possible Answers:

AAGGCTCGGAA

TTCCGAGCCTT

UUCCGAGCCUU

AUGUGUTTCUG

CCTTAGATTCC

Correct answer:

UUCCGAGCCUU

Explanation:

Simply create a complementary strand of RNA with matching base pairs, but substitute uracil (U) for thymine (T), since RNA does not use thymine base pairs.

The answer choice starting with AUG might seem appropriate since it is the start codon, however, realize that the rest of the base pairs do not match up to the DNA template. Further, RNA templates do not begin right at the start codon; there are promotoer and enhancer regions of DNA that are transcribed well before the first exon is transcribed with its AUG start codon.

Example Question #12 : Central Dogma

Eukaryotic DNA is packed in a chromatin structure, making it hard for DNA to be transcribed. What proteins are associated with the packing of DNA? 

Possible Answers:

Actin

Polymerases

Histones

Myosin

Collagen

Correct answer:

Histones

Explanation:

Histones are associated with DNA packed in chromatin. Acetylation of these histones allows for DNA transcription. Other proteins mentioned play no part in DNA chromatin structure.

Polymerases are active during DNA repair and transcription. Collagen is a fibrous protein associated with the extracellular matrix. Actin and myosin are myofilaments active in muscle contraction.

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