Transcript DNA RNA

Notes on Nucleic Acids
Chapter 8
2 types of nucleic acids:
DNA – deoxyribonucleic acid
RNA – ribonucleic acid
• organic compounds
• large, made of subunits called
nucleotides
 Click image
for interactive
journey into
human DNA
Each DNA nucleotide is made up of
3 parts:
1. Phosphate group
2. Deoxyribose – 5 carbon
sugar
3. Nitrogen base – either
adenine, thymine,
cytosine, or guanine
Nitrogen bases
Purines – adenine (A) and
guanine (G)
Pyrimidines – thymine (T) and
cytosine (C)
The bases are held together by weak
hydrogen bonds
Base pairings in DNA:
A–T
C–G
A model of DNA was constructed in
1953 at Cambridge University in
England
Scientist – James Watson, (1951-1953)
Field of study – biology
Country - America
Scientist – Francis Crick (1951-1953)
Field of study – biophysics
Country - England
Their model is described as a double
twisted helix
Watson and Crick published
their proposed DNA double
helical structure in a paper in
the journal Nature in April
1953. In this paper Watson
and Crick acknowledged that
they had been "stimulated
by.... the unpublished results
and ideas" of Wilkins and
Franklin.
(looks like a twisted ladder)
Scientist – Maurice Wilkins, (1950-1953)
Field of study – biophysics
Country - England
Scientist – Rosalind Franklin, (1951-1953)
Field of study – Molecular Biology
(x-ray diffraction)
Country - England
 Click
image for
interpretation of
the X-ray
The process by which DNA builds an
exact copy of itself - replication
• first the double helix must be
unwound – this is done by
enzymes called helicases
• then DNA polymerases (enzymes
which move along each DNA
strand) add nucleotides to the
exposed bases
Replication occurs every time a cell
divides, therefore passing the
DNA code on into every cell
Genes are the DNA-encoded
information that specifies
particular proteins;
Each gene is made of a specific
sequence of nucleotides
The working structures of genes are
made of RNA
RNA structure:
1. Consists of a single strand of
nucleotides
2. Ribose – a 5 carbon sugar
3. Uracil (U) instead of thymine (T)
uracil is paired with adenine
RNA base pairings: A – U
C–G
Three types of RNA
1. mRNA – messenger RNA
2. tRNA – transfer RNA
3. rRNA – ribosomal RNA
• All are needed for processing the
information from DNA into proteins
(gene expression)
Differences in DNA and RNA:
DNA
RNA
1. double stranded
single stranded
2. thymine
uracil
3. nucleus only
cytoplasm
4. deoxyribose sugar
ribose sugar
Gene expression occurs in two
stages:
1. Transcription – information in
DNA is transferred to
mRNA
2. Translation – the information in
mRNA is used to make a
protein
Roles of DNA & RNA in
transmitting genetic information
• Story time: the analogy…
• Comp Book– Draw the Flow Map: DNA
expression in the cell
• You need your pencil plus three colors:
–
–
–
–
Pencil will draw cell membrane/ cell parts/ labels
RED: DNA molecules
BLUE: any RNA molecules
PURPLE: protein
DNA  RNA
RNA  protein
1. Transcription (DNA  RNA)
• occurs in nucleus
• begins with the enzyme RNA
polymerase which binds to the
promoter
Promoter – a specific sequence of
DNA that acts as a “start” signal
for transcription
Terminator – a sequence of bases
that tells the RNA polymerase to
stop adding nucleotides
Transcription Video
mRNA – is an RNA copy of a gene
used as a blueprint for a
protein
• carries hereditary information
from DNA and delivers it to the
site of translation
• acts as a template for the
assembly of amino acids
tRNA – acts as an interpreter
molecule
• translating mRNA sequences
into amino acid sequences
rRNA – plays a structural role in
ribosomes
2. Translation (RNA proteins)
• occurs in cytoplasm @ a ribosome
—both free ribosomes &
ribosomes attached to ER
• uses nucleic acids to synthesize
proteins
• involves all three RNA types:
—rRNA in the ribosome
—mRNA containing the genetic
message
AUG-AAA-UAC-CCU-CCA-GCG-GGA
—message is made of codons
Codon – a series of three-nucleotide
sequences
• each codon corresponds to an
amino acid or signifies a start or
stop signal
Write this down!
—tRNA carrying specific
amino acids to be joined
a.a.
Translation
ribosome
mRNA
(Example)
AUG-AAA-UAC-CCU-CCA-GCG-GGA
UAC
GGU
tRNA
  UUU
   AUG
  
tRNA
Growing polypeptideGGA
Met
tRNA
Lys
tRNA
tRNA
Tyr
Pro
Ser
Translation:
mRNA, tRNA & rRNA in cooperative action
…to make proteins!!!
Translation
ribosome
mRNA
(Repeated)
AUG-AAA-UAC-CCU-CCA-GCG-GGA
UAC
GGU
tRNA
  UUU
   AUG
  
tRNA
Growing polypeptideGGA
Met
tRNA
Lys
tRNA
tRNA
Tyr
Pro
Ser
Translation Video
A “Polysome”
Can you ID the 3 RNAs?
Awesome summary video from
www.youtube.com
Click here to view