AP Review
Chapters 16-18
Fast Facts
The role of DNA in heredity was first studied by
using bacteria and viruses.
Griffith (1928) was studying streptococcus
pneumonia.
Transformation: a change in genotype and
phenotype due to the assimilation of external
DNA by a cell.
Avery (1944) purified various chemicals from
the heat killed bacteria to recreate Griffith’s
experiment. Only DNA worked.
Fast Facts
Hershey and
Chase performed
experiments
showing that DNA
is the genetic
material of T2 (a
type of phage).
Fast Facts
The monomer of nucleic acids are
nucleotides
- each consists of 3 parts: a
nitrogenous base, a pentose sugar
called deoxyribose, and a phosphate
group.
- the base can be adenine (A), thymine
(T), cytosine (C), or guanine (G).
Fast Facts
Fast Facts
A series of enzymes carries out the steps
of DNA replication
DNA Polymerase: enzyme that catalyzes
the elongation of new DNA
DNA strands line up in an antiparallel
arrangement
5’-------------3’
3’-------------5’
Fast Facts
DNA polymerase adds nucleotides only to
the free 3’ end of a growing DNA strand.
A new DNA strand can elongate only in
the 5’  3’ direction.
- leading strand: DNA strand made by
this mechanism; works toward the
replication fork
Fast Facts
To elongate the other strand,
polymerase must work in the
direction away from the
replication fork. This is the
lagging strand
- Okazaki fragment
- DNA ligase: joins Okazaki
fragments to make a single
DNA strand
Fast Facts
Transcription and Translation are the two
main processes linking genes to
proteins
- transcription is the synthesis of RNA
under the direction of DNA
- translation is the actual synthesis of a
polypeptide, which occurs under the
direction of mRNA
Fast Facts
Nucleotide triplets specify
amino acids
- there are only 4
nucleotides to code for
the 20 amino acids
- triplet code: the
genetic instructions for
a polypeptide chain are
written in the DNA as a
series of three
nucleotide words
Fast Facts
- the codon AUG has a dual function: it codes
for the amino acid Methionine (Met) and it
functions as a “start” signal, or initiation
codon
- RNA polymerase: connects the RNA
nucleotides as they base-pair along the DNA
template
Fast Facts
In translation, the cell
interprets the genetic
message and builds a
protein accordingly
- transfer RNA (tRNA):
transfers amino acids
from the cytoplasm’s
amino acid pool to a
ribosome
- contains an
anticodon that is
complementary to the
mRNA codon
Fast Facts
Sample Question
Describe the steps of protein synthesis,
beginning with the attachments of a
messenger RNA molecule to the small
subunit of a ribosome and ending with
the release of the polypeptide from the
ribosome. Include in your answer a
discussion of how the different types of
RNA function in this process.
Fast Facts
A virus is a genome enclosed in a protective
coat
- a virus can be a DNA virus or an RNA virus
depending on the kind of nucleic acid
- the protein shell that encloses the viral
genome is called the capsid
Some viruses have viral envelopes,
membranes that cloak their capsids
- derived from the membrane of a host cell
Fast Facts
Fast Facts
Phages replicate using either the lytic or
lysogenic cycle
Lytic cycle: reproductive cycle that culminates
in the death of the host.
- during the last stage of the cycle the cell
breaks open (or lyses) and releases the
phages that were produced
Lysogenic cycle: replication of the phage
genome without destroying the host
Fast Facts
Fast Facts
Retrovirus
- most complicated reproductive cycle of
viruses
- refers to the reverse directional flow of the
genetic information
- contain reverse transcriptase: transcribes
DNA from an RNA template
- RNA  DNA directional flow
- DNA integrates as a provirus in the host cell
Fast Facts
Fast Facts
The control of gene expression enables
bacteria to adjust their metabolism to
environmental change
The lac operon: regulates the synthesis of
the enzymes needed to metabolize
lactose.
Fast Facts
-w/out lactose, no emzymes are made for
metabolism
- the regulatory gene, lacI is producing
a repressor (prevents the transcription
process) which blocks the RNA
polymerase from working
Fast Facts
Fast Facts
- when lactose is present, an inducer
binds to the repressor making it inactive
- RNA polymerase can then begin the
transcription process and the gene can
be expressed
Fast Facts
Sample Questions
Describe the operon hypothesis and
discuss how it explains the control of
messenger RNA production and the
regulation of protein synthesis in
bacterial cells.