Download 24 DNA

Nucleic Acids
(How much do you recall?)
- Structure
- Replication
- Packaging
Refer to chapter 12.1, 12.2 in text.
Types of organic molecules; 3 of 4
Nucleic Acids
Polymers of 4 nucleotides
Uses: Information transformation
from cell generation to generation (DNA)
and from genome to protein (RNA)
DNA replication
(making sure that all cells get the same information),
Transcription
(DNA sequence directing RNA sequence), and
Translation
(RNA directing amino acid sequence
in proteins).
(What do you recall about nucleic acid structure?)
- Structure
Note:
- nucleotides have three parts, which are…
- differences between DNA and RNA…
covalent
bonds
here
←
hold 3D
structure →
NB
↓ triphosphate
actually a nucleoside
Note:
-complementary base pairing
-held together by hydrogen bonds,
-to form the double helix.
-Chains run in opposite directions:
antiparallel
H bonds
original.britannica.com/eb/art-106485/The-hum...
Campbell CD 16.1 (1st and 2nd)
http://www.pbs.org/wgbh/nova/body/DNA-photograph.html
www.web-books.com/MoBio/Free/Ch3A5.htm
↑explanation of photo 51
organization of eukaryotic DNA
Unique DNA: found only one time in a given genome.
- These are often protein coding segments,
which tend to vary little or none between individuals,
and even between species.
- RNA- and protein-coding DNA is about 1.5% of the human genome.
Repetitive DNA: uh, repeated sequences.
typically 5-300 base pairs in length,
repeated up to 105 times per genome.
- Most of the non-coding DNA is repetitive.
transposons can “jump” about the genome
by cut/copy and paste of DNA
retrotransposons are reverse-transcribed segments from RNA
satellite DNA: short repeats (many copies)
often clumped at centromere and telomeres.
- Often used to evaluate evolutionary relatedness.
- These areas are used in forensic DNA “fingerprinting”.
(19.4 in text)
- Replication
Why would DNA have to be replicated?
(Note - answer isn’t written here.)
Again, what do you recall of the process?
Helix “unzips”.
DNA nucleotides brought in
and plugged in to proper pair.
Result of this semi conservative replication
is two identical strands,
each composed of one old and one new strand.
Campbell text animations,
chapter 16.2 (1st and 2nd activities)
YouTube videos:
http://www.youtube.com/watch?v=teV62zrm2P0
Brief, includes helicase, SSBP, Pol III, I,
okazaki fragments, ligase
http://www.youtube.com/watch?v=4jtmOZaIvS0
Less detail, more realistic
a quick summary… in French
Replication terms:
origin of replication
replication fork
replication bubble
helicase
→ topoisomerase aka
→ gyrase
single-stranded binding protein
primase (RNA polymerase)
primer
deoxynucleoside triphosphate
template strand
leading strand
lagging strand
5’ to 3’ direction
DNA polymerase III
DNA polymerase I
Okazaki fragments
ligase
→nucleotide excision repair
Animations are helpful here,
→telomere
or work from the text.
→telomerase
www.accessexcellence.org/RC/VL/GG/nucleosome.php
- In eukaryotes, DNA is wrapped around proteins called histones.
DNA
packaging - 8 histones are wrapped in two loops of DNA,
held in place by a linker (here H1) histone.
This is a nucleosome.
- This aids in organizing/ further packaging of DNA
and has a role in gene regulation.
You have about 2 m
of DNA in every cell!
↑ Linker histones stabilize this packing, too.
← Double helix
← Nucleosomes
← Euchromatin fiber
(during G phases)
When it comes time for cell division,
the DNA will be further “crunched”
← into heterochromatin…
Video showing packaging
http://www.youtube.com/watch?v=bW5JnYZImJA
http://www.geneticengineering.org/chemis/Chemis-NucleicAcid/Graphics/Pack.gif
Editing:
1. Base pair shape leads to proper matching.
2. DNA polymerases check and correct the work.
3. Subsequent proofing can catch errors later.
↓
http://en.wikipedia.org/wiki/DNA_repair
but some errors will squeak by…
http://www.nature.com/scitable/topicpage/dna-replication-and-causes-of-mutation-409
… which leads to genetics.
DNA replication in prokaryotes
The differences between eukaryotic and prokaryotic DNA:
- Prokaryotes have a lone loop of double-stranded DNA.
- It is not packaged in nucleosomes.
(At 1 mm, still 500 times length of cell...)
- Bacteria may have plasmids – independent DNA loops.
Comparing the replication processes:
- Cell division is organism’s reproduction: binary fission
Recall: Not mitosis, because…?
- Similar enzymes are at work:
helicase, SSB proteins, Pol III, Pol I, ligase….
- Still antiparallel,
so Okazaki fragments made.
- One origin of replication ….
www.sciencebuddies.org/mentoring/plugin_bacte...
Why does DNA need to be replicated?
Why do prokaryotes not have mitosis?
What are the bases?
Match each with its base pair.
Which are the purines?
Explain leading vs. lagging strand.
“Draw and label a simple diagram
of the molecular structure of DNA.”
3.3.5
List all of those DNA replication proteins.
Describe what each does.
Nucleosome?
Walk through the process of
eukaryotic DNA replication.
The rest of the terms
DNA replication
genome
transcription
repetitive DNA
translation
transposon
nucleotide
retrotransposon
pyrimidine
satellite DNA
purine
semi conservative
nucleoside triphosphate
histone
complementary base pairing
nucleosome
double helix
euchromatin
antiparallel
heterochromatin
unique DNA
plasmid
DON’T FORGET THE VOCABULARY PULLED EARLIER!