Chem 4

Front 1

What are some differences between the structures of DNA and RNA?

Back 1

RNA contains ribose, while DNA contains deoxyribose (the 2'-hydroxyl group is missing).
RNA uses uracil in place of thymine (both are pyrimidines).

Front 2

What is a phosphodiester bond and how does it form the backbone of nucleic acids (DNA
and RNA)?

Back 2

A phosphodiester bond consists of a phosphate group that links two adjacent ribose
molecules together at their 3' and 5' hydroxyl groups. A long chain of these forms the
backbone of DNA and RNA. The DNA bases are not directly involved in the backbone of
nucleic acids. They only serve to bind two separate strands together by hydrogen bonding.

Front 3

Compare endonuclease and exonuclease.

Back 3

Endonucleases cut nucleic acids in the middle of the strand whereas exonucleases cut from
the ends.

Front 4

Why is dsDNA (double stranded DNA) said to be antiparellel?

Back 4

One strand is oriented in a 5' to 3' direction and the other in a 3' to 5' direction. The DNA
sequence is always read in the 5' to 3' direction, however.

Front 5

Know the forces holding two strands of DNA together.

Back 5

Hydrogen bonds between bases (G-C pairs have 3; A-T pairs have 2), and base stacking
(hydrophobic forces).

Front 6

What is a plasmid?

Back 6

A plasmid is a small circle of DNA often found in bacteria. It is not part of the chromosome
and replicates independently. It often contains genes that confer resistance to antibiotics, and
it can be passed easily from one bacteria to another.

Front 7

Why is DNA replication called semiconservative replication?

Back 7

This means that after a section of DNA has been copied, each of the two new strands has
one copy of the original strand and one copy of a new strand.

Front 8

Where does the energy for DNA synthesis come from?

Back 8

Each nucleotide that is added is a dNTP (deoxy-nucleotide-triphosphate), that is, ATP,
CTP, GTP, or TTP. As each is added, two phosphate groups are released as pyrophosphate.
Breaking of these high-energy bonds make the reaction favorable.

Front 9

What are nucleoside analogs used for?

Back 9

These modified nucleosides block DNA synthesis by working as "imposters". They get
incorporated in to DNA but do not allow further replication. They are used as anti-cancer and
anti-viral drugs. One of nucleoside analogs used in HIV therapy is AZT (azidothymidine) and
its derivatives.

Front 10

What are histones?

Back 10

They are proteins which are positively charged and interact with the negatively charged
DNA to help it fold into nucleosomes. H2A, H2B, H3, and H4 form the core of the
nucleosome. H1 helps link adjacent nucleosomes together to form more compact structures.
DNA wraps around the nucleosome core about two times. During DNA replication, new
histones must also be made to help package the new DNA.

Front 11

Distinguish between mRNA, rRNA, and tRNA.

Back 11

mRNA is the "copy" of the gene produced during transcription which is translated into
protein at the ribosome. rRNA consists of four different sized strands of RNA which are
essential parts of the ribosomal structure (rRNA + protein), important for translation. tRNA
serves as an amino acid carrier that binds to the ribosome-mRNA complex and adds one
amino acid on to the growing peptide chain.

Front 12

RNA facts:

Back 12

80% of RNA in a cell is rRNA, 15% tRNA, 5% mRNA
mRNA has a 7-methylguanosine cap at its 5' end and a poly-A tail at its 3' end
introns are removed from the primary RNA transcript (hnRNA), while the exons remain to
make up the mRNA
the anticodon loop of tRNA binds to the codon of mRNA within the ribosome
Skip the details except for the first line of the answer!

Front 13

Posttranscriptional processing of RNA:

Back 13

synthesis of guanosine cap at 5’ end of RNA
polyadenylation of RNA at the 3’ end
methylation of some nitrogenous bases
removal of intron sequences
You may skip this question for now!

Front 14

Give an example of DNA replication inhibitor:

Back 14

Actinomycin D (dactinomycin) irreversibly binds to the double stranded DNA. In this way
it also stops transcription process(!). Used as anticancer drug.

Front 15

Give an example of transcription inhibitor:

Back 15

Rifampin inhibits a bacterial subunit of RNA polymerase. Used in the treatment of
pulmonary tuberculosis and leprosy.

Front 16

Give an example of translation inhibitor:

Back 16

Tetracycline is an antibiotic used to treat a variety of bacterial infections (nonsequence
selective).
Antisense oligonucleotide selectively stops translation by binding to specific sequences of
mRNA.

Front 17

How do the antibiotics, rifampin and dactinomycin work?

Back 17

They both block transcription. Rifampin blocks initiation by binding to RNA polymerase.
Dactinomycin blocks elongation by binding to the template DNA.

Front 18

What is the genetic code?

Back 18

Any aminoacid is encoded in the DNA sequence in the form of trinucleotide (codon).

Front 19

What are nitrogenous bases catabolized into?(!!!)

Back 19

Purine bases are catabolized into uric acid, which is excreted into urine.
Pyrimidine bases are either catabolized to CO2, H2O and urea or b-aminoisobutyric acid
excreted in urine.

Front 20

How is proofreading of a new DNA sequence accomplished?

Back 20

DNA polymerase recognizes an improper base pair and uses its 3'-5' exonuclease activity to
remove it. It then refills the space correctly. You may skip this question for now!