UNIT 6 AP BIO EXAM REVIEW 2025
QUESTIONS AND ANSWERS
TOPIC 6.1 DNA and RNA Structure - ANS ENDURING UNDERSTANDING: Heritable information
provides for continuity of life.
LEARNING OBJECTIVE
IST-1.K Describe the structures involved in passing hereditary information from one generation
to the next.
ESSENTIAL KNOWLEDGE
IST-1.K.1 DNA, and in some cases RNA, is the primary source of heritable information.
IST-1.K.2 Genetic information is transmitted from one generation to the next through DNA or
RNA—
a. Genetic information is stored in and passed to subsequent generations through DNA
molecules and, in some cases, RNA molecules.
b. Prokaryotic organisms typically have circular chromosomes, while eukaryotic organisms
typically have multiple linear chromosomes.
IST-1.K.3 Prokaryotes and eukaryotes can contain plasmids, which are small extra-
chromosomal, double-stranded, circular DNA molecules.
LEARNING OBJECTIVE
IST-1.L Describe the characteristics of DNA that allow it to be used as the hereditary material.
ESSENTIAL KNOWLEDGE
IST-1.L.1 DNA, and sometimes RNA, exhibits specific nucleotide base pairing that is conserved
through evolution: adenine pairs with thymine or uracil (A-T or A-U) and cytosine pairs with
guanine (C-G)—
a. Purines (G and A) have a double ring structure.
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,b. Pyrimidines (C, T, and U) have a single ring structure.
What is the significance of this famous experiment (what does it demonstrate)? - ANS the
Hershey-Chase experiments were a series of experiments conducted in 1952 by Alfred Hershey
and Martha Chase that helped to confirm that DNA is genetic material. While DNA had been
known to biologists since 1869, many scientists still assumed at the time that proteins carried
the information for inheritance because DNA appeared to be an inert molecule, and, since it is
located in the nucleus, its role was considered to be phosphorus storage. In their experiments,
Hershey and Chase showed that when bacteriophages, which are composed of DNA and
protein, infect bacteria, their DNA enters the host bacterial cell, but most of their protein does
not. Hershey and Chase and subsequent discoveries all served to prove that DNA is the
hereditary material.
How did Crick, Watson, Franklin and Wilkins contribute to our knowledge of DNA? -
ANS Combined, they revealed the double helix structure of the DNA molecule.
Draw a plasmid. Where are plasmids found in Prokaryotic cells? Where are they found in
Eukaryotic cells (HINT consider the evolution of some Eukaryotic organelles!)? -
ANS Plasmids are small rings of DNA free floating inside Prokaryotes. They are also found in
mitochondria and chloroplasts (consider the Endosymbiotic Theory that these organelles were
once free-living prokaryotes)
Come up with some way to remember (to link the facts together) that A and G are Purines and
have a double ring, while C, T, and U are Pyrimidines and have just one ring. Then share your
idea with someone and see what idea they came up with! - ANS A and G got married and
have 2 wedding rings
C, T, and U build pyramids with one ring
Briefly explain in your own words how the base pairing rules of DNA lead to its ability to be
used as the hereditary material of life (aka, to be copied and passed to a resulting daughter
cell). - ANS The base pairing rules for DNA are governed by the complementary base pairs:
adenine (A) with thymine (T) in an A-T pairing and cytosine (C) with guanine (G) in a C-G pairing.
2 Copyright ©2025 BRAINBARTER ALL RIGHTS RESERVED
, Conversely, thymine only binds with adenine in a T-A pairing and guanine only binds with
cytosine in a G-C pairing.
A always matches with T, and G always matches with C.....but why?
Proofreading enzymes run along the DNA molecule to be sure there are no mis-pairings
between bases, but how do they know when a mistake has happened? - ANS complementary
bases
Consistent pairings of complementary bases allow cells to make double-stranded DNA from a
single strand template, create messenger RNA from DNA and synthesize proteins from
individual amino acids by matching nucleotides bases on messenger RNA with their
complementary bases on transfer RNA.
DNA proofreading is an essential phenomenon during the synthesis of new DNA strands
because if there is a misincorporation of any nucleotide, it will cause mutation and ultimately
damage the cell's cellular processes. Thereby, the cell keeps track of any misincorporation of
nucleotide with the help of the enzyme DNA polymerase.
Based on their structure (shape) explain why purines must always match with pyrimidines. In
your explanation, include how a proofreading enzyme would identify a location where two
purines are accidentally matched up, and a location where two pyrimidines are matched up. -
ANS Purines pair with pyrimidines because their size and shape make them a perfect fit for
hydrogen bonding
Okay, but why can't T (a pyrimidine) match with G (a purine)?
Based on the number of hydrogen bonds that are available in adenine, thymine, guanine and
cytosine, explain why A always matches with T, and C with G. In your explanation, include how
a proofreading enzyme would identify a location where G and T are accidentally matched up,
and a location where A and C are matched up. - ANS The best explanation for why adenine
bonding with thymine only and guanine with cytosine only is through the base pairing rule in
DNA where the bases only have a set of available bonds to allow complementary base pairing,
where each base can only bond with a specific base partner. These hydrogen-bonded
nitrogenous bases are called base pairs. In complementary base pairing, cytosine can make
three hydrogen bonds with guanine, and adenine can form two hydrogen bonds with thymine.
The structures complement each other like a lock and a key system.
3 Copyright ©2025 BRAINBARTER ALL RIGHTS RESERVED
QUESTIONS AND ANSWERS
TOPIC 6.1 DNA and RNA Structure - ANS ENDURING UNDERSTANDING: Heritable information
provides for continuity of life.
LEARNING OBJECTIVE
IST-1.K Describe the structures involved in passing hereditary information from one generation
to the next.
ESSENTIAL KNOWLEDGE
IST-1.K.1 DNA, and in some cases RNA, is the primary source of heritable information.
IST-1.K.2 Genetic information is transmitted from one generation to the next through DNA or
RNA—
a. Genetic information is stored in and passed to subsequent generations through DNA
molecules and, in some cases, RNA molecules.
b. Prokaryotic organisms typically have circular chromosomes, while eukaryotic organisms
typically have multiple linear chromosomes.
IST-1.K.3 Prokaryotes and eukaryotes can contain plasmids, which are small extra-
chromosomal, double-stranded, circular DNA molecules.
LEARNING OBJECTIVE
IST-1.L Describe the characteristics of DNA that allow it to be used as the hereditary material.
ESSENTIAL KNOWLEDGE
IST-1.L.1 DNA, and sometimes RNA, exhibits specific nucleotide base pairing that is conserved
through evolution: adenine pairs with thymine or uracil (A-T or A-U) and cytosine pairs with
guanine (C-G)—
a. Purines (G and A) have a double ring structure.
1 Copyright ©2025 BRAINBARTER ALL RIGHTS RESERVED
,b. Pyrimidines (C, T, and U) have a single ring structure.
What is the significance of this famous experiment (what does it demonstrate)? - ANS the
Hershey-Chase experiments were a series of experiments conducted in 1952 by Alfred Hershey
and Martha Chase that helped to confirm that DNA is genetic material. While DNA had been
known to biologists since 1869, many scientists still assumed at the time that proteins carried
the information for inheritance because DNA appeared to be an inert molecule, and, since it is
located in the nucleus, its role was considered to be phosphorus storage. In their experiments,
Hershey and Chase showed that when bacteriophages, which are composed of DNA and
protein, infect bacteria, their DNA enters the host bacterial cell, but most of their protein does
not. Hershey and Chase and subsequent discoveries all served to prove that DNA is the
hereditary material.
How did Crick, Watson, Franklin and Wilkins contribute to our knowledge of DNA? -
ANS Combined, they revealed the double helix structure of the DNA molecule.
Draw a plasmid. Where are plasmids found in Prokaryotic cells? Where are they found in
Eukaryotic cells (HINT consider the evolution of some Eukaryotic organelles!)? -
ANS Plasmids are small rings of DNA free floating inside Prokaryotes. They are also found in
mitochondria and chloroplasts (consider the Endosymbiotic Theory that these organelles were
once free-living prokaryotes)
Come up with some way to remember (to link the facts together) that A and G are Purines and
have a double ring, while C, T, and U are Pyrimidines and have just one ring. Then share your
idea with someone and see what idea they came up with! - ANS A and G got married and
have 2 wedding rings
C, T, and U build pyramids with one ring
Briefly explain in your own words how the base pairing rules of DNA lead to its ability to be
used as the hereditary material of life (aka, to be copied and passed to a resulting daughter
cell). - ANS The base pairing rules for DNA are governed by the complementary base pairs:
adenine (A) with thymine (T) in an A-T pairing and cytosine (C) with guanine (G) in a C-G pairing.
2 Copyright ©2025 BRAINBARTER ALL RIGHTS RESERVED
, Conversely, thymine only binds with adenine in a T-A pairing and guanine only binds with
cytosine in a G-C pairing.
A always matches with T, and G always matches with C.....but why?
Proofreading enzymes run along the DNA molecule to be sure there are no mis-pairings
between bases, but how do they know when a mistake has happened? - ANS complementary
bases
Consistent pairings of complementary bases allow cells to make double-stranded DNA from a
single strand template, create messenger RNA from DNA and synthesize proteins from
individual amino acids by matching nucleotides bases on messenger RNA with their
complementary bases on transfer RNA.
DNA proofreading is an essential phenomenon during the synthesis of new DNA strands
because if there is a misincorporation of any nucleotide, it will cause mutation and ultimately
damage the cell's cellular processes. Thereby, the cell keeps track of any misincorporation of
nucleotide with the help of the enzyme DNA polymerase.
Based on their structure (shape) explain why purines must always match with pyrimidines. In
your explanation, include how a proofreading enzyme would identify a location where two
purines are accidentally matched up, and a location where two pyrimidines are matched up. -
ANS Purines pair with pyrimidines because their size and shape make them a perfect fit for
hydrogen bonding
Okay, but why can't T (a pyrimidine) match with G (a purine)?
Based on the number of hydrogen bonds that are available in adenine, thymine, guanine and
cytosine, explain why A always matches with T, and C with G. In your explanation, include how
a proofreading enzyme would identify a location where G and T are accidentally matched up,
and a location where A and C are matched up. - ANS The best explanation for why adenine
bonding with thymine only and guanine with cytosine only is through the base pairing rule in
DNA where the bases only have a set of available bonds to allow complementary base pairing,
where each base can only bond with a specific base partner. These hydrogen-bonded
nitrogenous bases are called base pairs. In complementary base pairing, cytosine can make
three hydrogen bonds with guanine, and adenine can form two hydrogen bonds with thymine.
The structures complement each other like a lock and a key system.
3 Copyright ©2025 BRAINBARTER ALL RIGHTS RESERVED
