Download NITROGEN BASES in DNA

1/22/2013
• DNA molecule is a double helix—two
strands twisted around each other, like a
winding staircase.
Nucleotide
From DNA to PROTEINS
Hydrogen
bonds
Ch 9.2 & 9.3 – pages 194-200
Ch 10.1 – pages 208-214
Biology
Mrs. Stolipher
Sugar--phosphate
Sugar
backbone
Key
Adenine (A)
Thymine (T)
Cytosine (C)
Guanine (G)
NUCLEIC ACIDS are built from subunits
called
NITROGEN BASES in DNA
____________________
NUCLEOTIDES
NITROGEN BASE
PHOSPHATE
SUGAR
SUGAR in DNA is
________________
deoxyribose
DEOXYRIBONUCLEIC ACID
Backbone
(sides of ladder)
made of
PHOSPHATES
_____________
and
sugars
_____________
ADENINE A
_____________=
GUANINE = G
_____________
CYTOSINE = C
_____________
THYMINE = T
______________
No URACIL
Nitrogen bases =“Steps of ladder”
A
Phosphate
group
G
Deoxyribose
sugar
C
T
Image from:
Purines
(2 rings)
Pyrimidines
(1 ring)
http://www.tokyo-med.ac.jp/genet/picts/dna.jpg
http://www.tokyo© Pearson Education Inc, publishing as Pearson Prentice Hall. All rights reserved
1
1/22/2013
Discovering DNA’s Structure
Chargaff’s Observations
• In 1949, Erwin Chargaff observed that for each
organism he studied, the amount of adenine
always equaled the amount of thymine (A=T).
• Likewise, the amount of guanine always
equaled the amount of cytosine (G=C).
• However, the amount of adenine and thymine
and of guanine and cytosine varied between
different organisms.
• We refer to A=T & C=G as complementary
base pairs
Watson and Crick’s DNA Model
• In 1953, Watson and Crick built a model of DNA
with the configuration of a double helix, a “spiral
staircase” of two strands of nucleotides twisting
around a central axis.
• The double-helical model of DNA takes into account
Chargaff’s observations and the patterns on
Franklin’s X-ray diffraction photographs.
• In other words, they came up with the current
structure (double helix) of DNA
Wilkins and Franklin’s Photographs
• By analyzing the complex patterns on X-ray
diffraction photo, scientists can determine the
structure of the molecule.
• In 1952, Maurice Wilkins and Rosalind Franklin
developed high-quality X-ray diffraction
photographs of strands of DNA.
• These photographs suggested that the DNA
molecule resembled a tightly coiled helix and
was composed of two or three chains of
nucleotides.
Chromosome Structure in Prokaryotes
Approximately 5 million base pairs
3,000 genes
Chromosome
E. coli bacterium
Bases on the chromosome
DNA molecule in bacteria is:
SINGLE &
______________
______________
CIRCULAR
CYTOPLASM (NO nucleus)
Found in __________
© Pearson Education Inc, publishing as Pearson Prentice Hall. All rights reserved
DNA in EUKARYOTES is packaged
into chromosomes
DNA REPLICATION
http://www.paternityexperts.com/images/DNA--of
http://www.paternityexperts.com/images/DNA
of--life.jpg
Humans have approximately 3
billion base pairs (1 m long)
60,000 to 100,000 genes
If the diameter of the DNA (2 nanometers) was as wide as a
fishing line (0.5 millimeters) it might stretch as far as 21.2 km
(or 13.6 miles) in length which would all have to be packed
into a nucleus, the equivalent size of 25 cm in diameter.
That is some packaging!
• The process of making a copy of DNA is
called DNA replication.
• DNA replication occurs during the synthesis
(S) phase of the cell cycle, before a cell
divides.
2
1/22/2013
HOW IS DNA COPIED?
Figure 12–11 DNA Replication
Section 1212-2
The structure of DNA
explains how it can be
copied.
New strand
Each strand has all the info
needed to construct
matching
the __________other
half.
If strands are separated,
base--pairing rules allow
base
_____________
you to fill in the
complementary bases.
Original
strand
DNA
polymerase
Growth
DNA
polymerase
Growth
Replication
fork
Replication
fork
New strand
Nitrogenous
bases
Original
strand
Sites where strand separation and
replication forks
replication occur are called _____________
Image from: http://evolution.berkeley.edu/evosite/evo101/images/dna_bases.gif
REPLICATION STEPS
1.
1.Enzymes
Enzymes “unzip” molecule by breaking
Hydrogen bonds that hold the
_______________
strands together and unwind it.
DNA polymerase joins nucleotides
2. _______________
using original strand as template and
spell checks
______________for
errors.
3. Copying happens in
directions along the
multiple
__________
places
opposite
________
two strands & in
at once.
Roles of Enzymes in DNA
Replication
http://www.dnatube.com/video/365/DNA--Replication
http://www.dnatube.com/video/365/DNA
Chapter 10
Checking for Errors
Decoding the Information in DNA
• In the course of DNA replication, errors sometimes
occur and the wrong nucleotide is added to the new
strand.
• Traits, such as eye color, are determined by
proteins that are built according to
instructions coded in DNA.
• An important feature of DNA replication is that DNA
polymerases have a “proofreading” role.
• Proteins, however, are not built directly from
DNA. Ribonucleic acid is also involved.
• This proofreading reduces errors in DNA replication
to about one error per 1 billion nucleotides.
• Like DNA, ribonucleic acid (RNA) is a nucleic
acid—a molecule made of nucleotides linked
together.
3
1/22/2013
RNA- the Other Nucleic Acid
NUCLEOTIDES
Also made of ___________
RIBOSE instead
Sugar is _______
of deoxyribose.
SINGLE
RNA is _________ stranded
URACIL instead
Contains _________
of thymine.
http://images2.clinicaltools.com/images/gene/dna_versus_rna_reversed.jpg
• The instructions for making a protein are
transferred from a gene to a mRNA
molecule in a process called transcription.
3 KINDS OF RNA HELP WITH INFO
TRANSFER FOR PROTEIN SYNTHESIS
RIBOSOMAL
_________________RNA
(rRNA)
Combines with proteins to form
ribosomes
TRANSFER
_________________RNA
(tRNA)
Matches m-RNA codon to add correct
amino acids during protein synthesis
MESSENGER
_________________RNA
(mRNA)
carries code from DNA to ribosomes
rRNA and tt-RNA images from © Pearson Education Inc, publishing as Pearson Prentice Hall. All rights reserved
mRNA image from http://wps.prenhall.com/wps/media/tmp/labeling/1140654_dyn.gif
• The entire process by which proteins are
made based on the information encoded in
DNA is called protein synthesis.
• Cells then use tRNA & rRNA to read the
instructions on the mRNA molecule and put
together the amino acids that make up the
protein in a process called translation.
TRANSCRIPTION
Adenine (DNA and RNA)
Cystosine (DNA and RNA)
Guanine(DNA and RNA)
Thymine (DNA only)
Uracil (RNA only)
• takes place in nucleus of eukaryotes
• Is the transfer of Information from DNA
to RNA
RNA POLYMERASE
Enzyme called __________________
separates strands, then uses one
strand as a template to assemble an
RNA copy.
4
1/22/2013
How does RNA POLYMERASE know
where a gene starts and stops?
Enzyme binds to places with specific DNA
PROMOTERS
sequences called _______________.
RNA POLYMERASE
PROMOTERS
tell _________________
http://www.stolaf.edu/people/giannini/flashanimat/molgenet
ics/transcription.swf
where to start.
http://www.stolaf.edu/people/giannini/flashanimat/molgenet
ics/transcription.swf
RNA nucleotides which
RNA polymerase adds ________________
are complementary to the DNA strand in order
to make mRNA.
Signals at the end of the gene code cause
stop .
transcription to _____
http://images2.clinicaltools.com/images/gene/dna_versus_rna_reversed.jpg
http://images2.clinicaltools.com/images/gene/dna_versus_rna_reversed.jpg
The Genetic Code: Three-Nucleotide
“Words”
MASTER PLAN
DNA stays safe in nucleus
•
The RNA instructions are written as a series of
three-- nucleotide sequences on the mRNA
three
called codons.
•
The genetic code of mRNA is the amino
acids and “start” and “stop” signals
•
An anticodon is a threethree-nucleotide sequence
on a tRNA that is complementary to an
mRNA codon.
codon.
TRANSCRIPTION (DNA→
(DNA→ RNA)
& PROCESSING
takes place in nucleus
TRANSLATION (RNA→
(RNA→ proteins)
takes place on ribosomes
in cytoplasm
“Blueprints” of master plan
are carried to building site
http://www.home--improvement
http://www.home
improvement--resource.com/images/architect.jpg © Pearson Education Inc, publishing as Pearson Prentice Hall. All rights reserved
Codons in mRNA
RNA’s Roles in Translation
• The seven steps of translation are:
Step 1 The ribosomal subunits, the mRNA,
and the tRNA carrying methionine bind
together.
Step 2 The tRNA carrying the amino acid
specified by the codon in the A site arrives.
Step 3 A peptide bond forms between
adjacent amino acids.
5
1/22/2013
Step 4 The tRNA in the P site detaches and leaves
its amino acid behind.
TRANSLATION
Step 5 The tRNA in the A site moves to the P site.
The tRNA carrying the amino acid specified by the
codon in the A site arrives.
Step 6 A peptide bond is formed. The tRNA in the
P site detaches and leaves its amino acid behind.
Step 7 The process is repeated until a stop codon
is reached. The ribosome complex falls apart. The
newly made protein is released.
REPLICATION
DNA → DNA ____________
TRANSCRIPTION
DNA → RNA ____________
TRANSLATION
RNA→ Protein ___________
http://www.stolaf.edu/people/giannini/flashanimat/molgenetics/tr
anslation.swf
Concept Map
RNA
can be
Messenger
RNA
also called
Ribosomal
RNA
which functions to
Carry
Instructions
mRNA
also called
rRNA
from
to
DNA
Ribosomes
Transfer
RNA
which functions to
also called
Combine w/
proteins
tRNA
which functions to
Bring amino
acids to
ribosomes
to make up
Ribosomes
6