Download Unit 4

Chapter Sixteen











The three components of a nucleotide are phosphate, sugar, and base.
Deoxyribose is the sugar componenet of DNA, having one less hydroxyl group
than ribose, the sugar component of RNA.
The nitrogen bases found in DNA are adenine guanine cytosine, and thymine.
Adenine and cytosine are pyrimidines while guanine and thymine are purines.
I know the base pairing rule and its significance.
The structure of DNA is a double helix. The nitrogeneous bases project in to the
interior, where they hydrogen bond in specific pairs.
The Meselson and Stahl experimient demonstrated that DNA replication is
semiconservative, confirming Watson and Crick’s hypothesis that the parent
molecule unwinds and each strand then serves as a template for the the synthesis
of a new half-molecule according to base-pairing rules.
Replication begins at special sites called origins of replication. DNA polymerases
catalyze the synthesis of the new DNA strand. Simultaneously synthesis
antiparallel strands at a replication fork yields a continous leading strand and
short, discontinous segments of lagging strand. The fragments are later joined
together with the help of DNA ligase. DNA must start on the end of a primer, a
shrt segment of RNA synthesized by the enzyme primase. Helicase is an enzyme
that works at the crotch of the replication fork, untwisting the double helix and
separating the two “old” strands. Single-strand binding proteins then attach in
chains along the unpaired DNA strands, holding these templates straight until new
complementary strands can be synthesized.
The DNA strands are antiparallel; that is, their sugar-phosphate backbones run in
opposite directions.
The leading strand is the new continuous complementary DNA strand synthesized
along the template 5’→3’ direction. The lagging strand is a continuously
synthesized DNA strand that elongates in a direction away from the replication
fork.
I know how the lagging process is synthesized when DNA polymerase can add
nucleotides only to the 3’ end.
DNA polymerase proofreads each nucleotide and if one is incorrect it removes the
incorrectly paired nucleotide, and replaces it before continuing synthesis. In
excision pairing, a segment of the strand containing the damage is cut out by one
repair enzyme, and the resulting gap is filled in with nucleotides properly paired
with the nucleotides in the undamaged strand. The enzymes that fill the gap are a
DNA polymerase and DNA ligase.
Chapter Seventeen














I know the difference between RNA and DNA.
I know how information flows from gene to protein.
I can distinguish the difference between transcription and translation.
In eukaryotes transcription occurs in the nucleus and translation in the cytoplasm.
In general the processes in prokaryotic and eukaryotic cells are similar. The
major difference is the occurrence of RNA processing in the eukaryotic nucleus.
The mRNA base triplets are called codons.During translation, the sequence of
codons along a genetic message is decoded, or translated, into a sequence of
amino acids making up a polypeptide chain.
I can distinguish between mRNA, tRNA, and rRNA.
I know the structure of tRNA.
The given sequence in DNA is A T C, the mRNA is U A G, and the tRNA is A T
C.
The initiation stage of translation brings together mRNA, a tRNA bearing the first
amino acid of the polypeptide, and the two subunits of a ribosome. In the
elongation stage, amino acids are added one by one to the initial amino acid.
Termination stops translation.
I know the general rule of RNA polymerase in transcription.
A ribosome is made up of two subunits, the large and small subunits. The
structure reflects its function of bringing mRNA together with amino acid bearing
tRNA.
I know the difference between eukaryotic and prokaryotic mRNA.
In the eukaryotic nucleus mRNA is modified before it leaves to the cytoplasm.
Both ends of the mRNA molecule are altered. In some cases the molecule is cut
apart and parts of it are spliced together again.
The insertion or deletion of nucleotides may alter the reading frame of the triplet
grouping in mRNA. Substitution is less likely to cause harmful mutations.
Chapter Eighteen













A virus is a small nucleic acid genome enclosed in a protein capsid and
sometimes a membranous envelope. The genome may be DNA or RNA.
I know why parasites are obligate parasites.
Retroviruses use an enzyme called reverse transcriptase to synthesize DNA from
their RNA template. The DNA can then integrate into the host genome as a
provirus.
I know how viruses recognize host cells.
I know the difference between lysogenic and lytic cycles.
An existing virus can evolve and cause disease in individuals who had developed
immunity to the ancestral virus. Vaccines help fight vital infection.
Hepatitis B, Epstein virus, Papilloma virus, and HTLV-1. All tumor viruses
transform cells through the integration of viral nucleic acid into host cell DNA,
I know the similarities between viruses and living organisms.
The bacterial chromosome is a circular DNA molecule with few associated
proteins.
In transformation, naked DNA enters the cell from the surroundings. In
transduction, bacterial DNA is carried from one cell to another by phages. In a
primitive kind of mating, an f+ or Hfr transfers DNA to an F- cell.
The F plasmid carries genes for the sex pili and other functions needed for mating
in bacterial conjugation.
Cells control metabolism by regulating enzyme activity or by regulating enzyme
synthesis through the activation or inactivation of selected genes.
Regulatory genes are usually clustered together.
Chapter Nineteen



Eukaryotic genomes are more complex than prokaryotic. The control of gene
expression is also more complex in eukaryotes than in prokaryotes.
The current model for DNA packing involves coiling and folding, which
culminates in the highly condensed metaphase chromosome.
Heterochromatin is the condensed form of interphase chromatin. Euchromatin is
the more open, unfolded form of the chromosome.
Chapter Twenty





I know technology has helped scientist in the study of DNA.
I know the natural function of restricted enzymes.
I know two major genes for cloning.
I know what a probe is.
I know the importance of DNA synthesis.