Summary document of Chapter 5 Evolution and biodiversity IB Biology
Tema 3: Metabolismo
IB Biology Full Course Notes + Required Drawings Units 1 - 11 & Option D
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topic 7
:
Nucleic
Acids
7.1 DNA structure and replication .
7.2 Transcription and
gene expression .
7.3 Translation .
,⑨ Nucleosomes :
⑨
Eukaryotic DNA is al was associated with basic (alkaline ) and positively charged proteins called histones .
⑨
Prokaryotic DNA lacks histones, and is often referred to as naked DNA .
⑨ A nucleosome consists of a
length of DNA of about 150 base pairs wrapped around ,
a core of 8 histones (which are
actually
4 pairs
of 4 different histones ) t a special histone named H1 .
⑨ DNA is acidic and negatively charged ,
so the
bonding with the histones neutralizes the DNA .
⑨ The
nucleosomes are linked because the DNA strand from one nucleosome flows directly into the next nucleosome .
⑨ This section of DNA is called DNA linker .
⑨ Because some eukaryotes have
large genomes ,
a certain amount of packaging ( folding coiling , ,
and re -
coiling ) is required to fit
the genetic material into the nucleus .
⑨ Nucleosomes help to super coil the DNA while still access to it
ensuring appropriate .
⑨ Access to the coils unwind and histones
DNA occurs when are moved out of the way so that DNA can be copied I transcribed .
⑨ Nucleosomes be co side red to be the repeat units of chromatin, which is coiled to form chromosomes
can
eukaryotic further .
⑨ DNA replication :
⑨ DNA
replication relies base
on
paring .
⑨ The DNA molecule also needed to be stable because of its function as
genetic material .
⑨ Base
paring allows this stability of the double
-
helix due to :
2 hydrogen bonds between A and T
!
.
The hydrogen bonding between the purine and the pyramid ines .
3
hydrogen bonds between C and G .
he T and
slightly positive charge on a
slightly negative charge on A , allow the two bases to bond
together during
complementary base
paring .
⑨ Once it became clear that DNA forms double helix with antiparallel strands bonded
a -
together by complementary
base paring ,
a mechanism for DNA replication also presented itself .
⑨
If the double helix of-
a
single DNA molecule was separated each strand could
,
be used to create the matching new strand .
, ⑨ This would be done in two new identical molecules
through base
paring resulting
,
.
In DNA base paring ,
a
pyramid ine is
always
bonded to a purine .
Purines : A and G .
Pyramidin es : T and C .
⑨ Semi -
conservative Replication :
⑨ DNA
replication progresses in a semi conservative-
way .
⑨ The details between DNA replication differ between
eukaryotes and prokaryotes .
⑨ The main
difference in eukaryotes =
replication can be
initiated at various points along the DNA molecule , while it
be started at position prokaryotic DNA
can
only one on .
⑨ This
ensures more efficient DNA replication in eukaryotes .
DNA replication enzymes :
1. helicase 2. DNA 4. DNA
,
gyrase ,
3. DNA prima se , ligase ,
5. DNA polymerase I , 6. DNA polymerase III .
⑨ The rate of 100 nucleotides per and nucleotides for
replication is
approximately second in eukaryotes 1000
prokaryotes
⑨ The human ar round 3 billion base 6 billion base pairs have to be
genome has pairs per haploid set
of chromosomes, so
⑨
replicated during the S phase-
of the cell cycle .
⑨@ When a DNA molecule is replicated
DNA replica trio requires the information
of
, efficiency
2
is improved if
replication forks
it
.
progresses in 2 directions .
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