DNA, RNA, and the Flow of
Genetic Information
Nucleic Acid Structure

What structural features do DNA and RNA
share?
 Polymers of nucleotides
 Each nucleotide contains sugar,
phosphate, nitrogen containing base
 Each nucleic acid contains 4 different
nucleotides
Nucleic Acid Structure

What differentiates
DNA from RNA?
 Type of pentose
sugar
Nucleic Acid Structure

The nitrogen containing bases derived from
purine and pyrimidine
Nucleic Acid Structure

What makes up the backbone of the nucleic acids?
Nucleic Acid Structure
What contributes to the stability of nucleic
acids?
 Negative charge of phosphodiester bridge
 Repels nucleophiles
 What is the difference between a nucleotide
and a nucleoside?

Nucleic Acid Structure

What are the DNA nucleotides?
 Deoxyadenosine-5-phosphate
 Deoxyguanosine-5-phosphate
 Deoxycytidine-5-phosphote
 Deoxythymidine-5-phosphate
Nucleic Acid Structure

What are the RNA nucleotides?
 Adenosine-5-phosphate
 Guanosine-5-phosphate
 Cytidine-5-phosphate
 Uridine-5-phosphate
Nucleic Acid Structure

How is the base bound
to a sugar?
 -glycosidic
linkage
Nucleic Acid Structure

Nucleic acids show polarity and are always
written in the 5’ to 3’ direction
Nucleic Acid Structure

What doe this
photograph represent?
Nucleic Acid Structure

What are the major features of the double helix of
DNA?
 Two chains coiled around common axis running
in opposite directions
 Bases on inside, sugar-phosphate on outside
 Bases are 3.4Å apart
 Structure repeats ever 34Å
 Diameter = 20Å
Nucleic Acid Structure
Base pairing exists
 A with T
 C with G
 How did the work
of Chargaff support
this concept?

DNA Replication


DNA is said to
replicate
semiconservatively.
What does this mean?
How did Meselson
and Stahl demonstrate
this to be true?
DNA



How can the helical structure be disrupted?
 Heating
What is Tm?
 Melting temperature – half helical structure is
destroyed
What is hyperchromism?
 Single stranded DNA absorbs UV light more
effectively than double stranded DNA
DNA
DNA
DNA

Why is the ability to separate the two chains
of the double helix and reassociate them an
important tool in the laboratory?
 hybridization experiments
DNA

What is the difference between linear DNA
and circular DNA and where are each of
these forms found?
 circular – ends of molecule are linked
 linear – human DNA
 circular – bacterial DNA
DNA

What is supercoiled DNA?
Nucleic Acid Structures

What are stem-loop structures?
Nucleic Acid Structures

Other complex
structures of singlestranded nucleic acids
form
Nucleic Acid Structures

In some complex structures can get
hydrogen bonds formed between nonstandard base pairs
Nucleic Acid Structures
DNA Replication

What is DNA polymerase?
 enzyme that catalyzes addition of DNA
nucleotides to a growing chain of DNA
 (DNA)n + dNTP
(DNA)n+1 + PPi

What besides the enzyme is needed for DNA
synthesis?
 template
 primer
 activated nucleotides
DNA Replication

What is the nature of the reaction catalyzed by
DNA polymerase?
DNA Replication

What else can some DNA polymerases do?
 remove mismatched nucleotides
RNA Viruses
What is the difference between and RNA
virus and a retrovirus?
 RNA viruses replicate via an RNA
directed RNA polymerase
 retroviruses use reverse transcriptase to
replicate
 Examples of each?

Replication of Retrovirus
Gene Expression

How does RNA facilitate gene expression?
 m-RNA – carries information from DNA
 t-RNA – carries amino acids to site of
protein synthesis
 r-RNA – major component of ribosome
where proteins are made
 snRNA – (in eucaryotes only) – splices
RNA
Transcription

What does RNA polymerase do and how does it work?
Transcription

How does RNA polymerase differ from
DNA polymerase?
 doesn’t require primer
 doesn’t contain nuclease activity
Transcription

What are promoter sites and where are they
located?
 regions of DNA that bind RNA polymerase and
determine where transcription begins
Transcription

How does RNA
polymerase know
when to stop
transcribing?
 terminator sequence
 rho protein
Transcription

What happens to m-RNA in eukaryotes after
transcription?
Transcription

How does t-RNA serve as an adaptor molecule?
Transcription

What do we know about the genetic code?
 three nucleotides code for an amino acid
 code doesn’t overlap
 no punctuation
 code is degenerate
Genetic Code
Translation

What are the start and stop signals for translation?
 stop codons – UAA, UCA,UAG
Genetic Code
What evidence suggests that the genetic
code is universal?
 one can use machinery of one species to
translate m-RNA of a different species
 There are some variations in genetic code
 mitocondrial DNA
 DNA from cilliates

Genetic Code

What are introns and exons?
 introns – non-coding sequences of DNA
 exons – coding sequences of DNA
RNA Processing

How are introns correctly removed before translation?
 splicosomes – proteins and small RNA molecules
Exons and Introns

Why are many genes in higher eukaryotes
discontinuous?
 exons code functional domains in
proteins
 can shuffle exons to produce new
proteins
 can generate related proteins by splicing
m-RNA differently