Grade 12 IEB Life Science Genetics Summary notes

Unit 1 : DNA i. RNA
NUCLEIC ACIDS

→

organic molecules
→
control synthesis of proteins in All living things
→
stores and transfers genetic information .




/
2 TYPES
DNA RNA
:




DNA (deoxyribonucleic acid) .

Double helix .




Single strand

RNA ( n.bonuaeicaa.gg g. deoxyribose g. ribose
. .




A C. G- T A,C , G. U
' '




, ,

A =T G- =L it
and
any sequence ratio
'




DNA

location :
nucleus →
chromosomal DNA
outside nucleus → extranuclear DNA [mitochondria / chloroplasts]

Chromosomes i. genes

•

Chromosome Thread : -
like
,
composed of DNA , wrapped around histones (protein)
Only visible in dividing stage
>
DNA



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histone


structure of a chromosome



•

Gene : A short
segment of DNA that codes for a
particular protein
↳ determines characteristics of
organism .




Scientists :B James Watson i. Francis Crick =
formulated double helix structure .




* Erwin chargaff Equal number = of A bases to T and C bases to G- in DNA molecule .
->
Base pairing
to Maurice Wilkens i. Rosalind Franklin = ✗ ray of chromosome
-
→ helix shape rule !

↳ helped Watson i. trick .




Structure : Nucleotides :
f p




B
S
Sugar
→
→
Giant molecule molecule [ Deoxyribose]
- pentose sugar
Phosphate phosphatedi ester
→
→
2 strands
bond
'

→
Double helix Nitrogenous base
→

- ,

t
anti Adenine
}
→
parallel
°
-




→
Polymer
.


Thymine
nucleotides cytosine
} A i. G- Purines Large
•
→
monomers : = >

•
Gaunine C IT =
Pyrimidines >
Small

, Formation of DNA :



Sugar phosphate 1 strand complement of the other !
sugar + phosphate
→
I . + =
2 strands is

-
,



alternating in strands frame
✓



2.
Rung =
2 bases link by weak
hydrogen bonds (broken by enzymes) nucleotides
[1 pyrimidine]
large purine + 1 small u



AKA BASE PAIRS
:
polynucleartides

DÑA
A -7
}
° →
2 It bonds of bases to form base pairs
equal number
-



.




°
G- C - →
3 H bonds
-
'


. . A =
T i. G- =L u




wraps around histone
-


Base pairs occur in any sequence u


→
sequence of bases =
code →
instructions for protein synthesis chromatin
↳ I
' ' '


genetic
'
code or code of life

condense +
super coil
Mitochondrial DNA (mtDNA) v



chromosomes
-

Not related to chromosomal DNA
-

Shorter + circular
'


Genes code for
enzymes
→ cellular
respiration .




Endosymbiosis (origin of mitochondria) bacterium as prey entered single cell avoided digestion independent
'

→ → →
cell

(own DNA)
'


Relatedness : -
mitochondria of sperm @ base of tail
maternal mitochondria ian
'




zygote only contains :
-

.
.




↳ used to trace maternal lines [ mtDNA corresponds = more closely related)
-



mtDNA =
no mutations or
changes in meiosis [ relatively unchanged]
µ '
mitochondria



Role of DNA

•
GENES :
has specific sequence of
nitrogenous bases
↳ of amino acids that will form a
determines sequence i. type protein

NON CODING DNA No instructions for protein synthesis
°
-
: -




junk
'

-

Not DNA
-


used in DNA fingerprinting
→
non -



coding DNA =
different for everyone .




lies between chromosome
genes
-

✓ on .




functions : -



Regulates { controls expression of
genes in coding DNA
'

off
'
When / Where
'
-




genes are switched in or

-


Protects genes from mutations
controls process of copying genes during transcription
-


.

, Replication of DNA
MMhthiainpssibe-andsgfhi.si one
-




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-
chromatid
a




Duplication of DNA [2 IDENTICAL copies] *
⑥ replication
centromere

Takes place Interphase (cell performs activities)
§
→
normal
9




a


chromosome duplicates → 2 identical chromatids
µ ☒&
↳ held together by centromere DNA


chromosome Chromosome
before after
sister chromatids
Process i. Double helix unwinds into 2 strands
( identical)

f)
⑧
2. Weak H bonds break
-
: strands unzip
3. Free floating nucleotides complementary = strands for original strands 5. 2 chromatids
U
.




↳
joined by enzymes [ DNA polymerase] make 1 chromosome .




4.
Original strand =
template chromosome


-
: strand now =
'

I new
'

strand i. 1
original strand .
( still identical) →
Semi conservative replication
-




Importance →
Mitosis : mother cell ÷ =
2 identical
daughter cells

d
identical info
makes copies of DNA :
daughter cell =
same genetic .




RNA

location : -

nucleus & cytoplasm Nucleotides :




part of ribosomes ribose
Sugar
-
• -




•

Phosphate
structure single strand
Nitrogenous bases A. G. C. Uracil
:
- ° :



Polymer ↳ can
occur in
any ratio
-




→
monomers =
nucleotides

cytoplasmic streaming
→
moves with


3 types of RNA


i. Mess anger RNA (mRNA)
-



single strand
-


forms in nuclear plasm (DNA template)
* carries
genetic code from DNA in nucleus to
ribosomes in cytoplasm .




&yf
2. Transfer RNA (tRNA)
Single strand that loops
-




cytoplasm
-




3 exposed bases anticodon
-

=




* Picks up amino acids in
cytoplasm and anticodon a
-

transfers them to ribosomes for protein synthesis .

Structure of tRNA


3. Ribosomal RNA (rRNA)
-




single strand

part of ribosome controls protein synthesis
-

+ .




helps ribosome read codon
-