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THE NUCLEUS
• Most plant and animal cells have a welldefined nucleus surrounded by a
double, permeable nuclear membrane
made up of proteins and phospholipids
• Ribosomes occur on the outer
membrane and these are concerned with
protein synthesis.
• The nucleoplasm is the matrix, in which
various substances are suspended.
• There may be one or more nueleoli
[singular = nueleolus] in the nucleus.
These contain proteins and nucleic acids
found within the nucleus and they
manufacture RNA and are concerned with
protein synthesis.
• Chromosomes are long threads made of
DNA and some protein. They are the
carriers of GENES which are responsible
for our hereditary traits. When a cell Is
not dividing the chromosomes are not
visible but are in a very tangled mass, the
chromatin network
FUNCTIONS OF THE NUCLEUS
• Controls metabolic activities of the cell by
dictating the type of proteins to be
manufactured.
• Carries hereditary traits and allows the
transmission of these from parent to
offspring.
During cell division, the chromatin is visible as
chromosomes. Chromosomes are the control
centres of the nucleus
Chromosomes
• They are rod-shaped, seen clearly during
cell division. They consist of a core of
DNA
_________,
surrounded by a protein
matrix (chromatid)
•
• The DNA (DeoxiriboNucleic Acid) is a
double helix, which means it is like a
twisted ladder. DNA is made of buildingnucleotides
blocks called ______________________.
• You have heard of GENES (not
JEANS!). A gene is a segment of DNA
and it controls the making of specific
proteins in the body, making that body
unique and different. Let us look at how
this happens.
1
DNA – The Molecule of Life
Hidden in all life is a
unique code
This code is in the form
of a chemical, called DNA
DeoxyriboNucleic Acid
2
Where is DNA found in the cell?
One
chromosomes
enlarged
Genes are
Chromosomes
pieces
ofcell
DNA
in the
thatnucleus
code for a
Chromosome
characteristic
uncoiled
e.g. Eyeto
show
DNA
colour
3
DNA – The Molecule of Life
What does DNA look like?
A photo of DNA from an electron
microscope
4
DNA – The Molecule of Life
We can’t see too much from this but if we
look at the molecules that make up DNA we
see a a truly amazing molecule – one that
contains the hidden code of all life on earth
5
DNA – The Molecule of Life
What is DNA made up of ?
What results if a DNA molecule like this
is broken down?
6
DNA – The Molecule of Life
DNA is found to be made of three
types of molecules:
7
DNA – The Molecule of Life
Sugar
This is a special
type of sugar called
deoxyribose
8
DNA – The Molecule of Life
Phosphate
Similar to the chemicals used
as fertilisers to grow plants
9
DNA – The Molecule of Life
Base
D
O
O
M
Similar to the chemicals
used in insecticides –
NITROGENOUS BASE
10
DNA – The Molecule of Life
SUMMARY: DNA is made of
three types of molecules
Sugar
Phosphate
Nitrogenous Base
• A DNA profile of a
person can be made
from these sources!
• Police and forensic
scientists use this
information in criminal
investigations!
• This is known as DNA
fingerprinting. No two
people except identical
twins have the same
DNA
DNA STRUCTURE
• DNA [DeoxyriboNucleic Acid] is known as
the key to life. It is the hereditary material
found in the chromosomes as well as
other parts of the cell e.g. mitochondria.
• It is a very long
giant molecule
made up of
smaller units
called
NUCLEOTIDES.
Watson & Crick
were awarded the
Nobel Prize for
working out its
structure [although
a South African
woman was just
pipped at the post
(1953-1962)].
• Each side is made up of alternating
SUGARS [deoxyribose] and
PHOSPHATES.
• Forming the 'rungs' are PAIRED
NITROGENOUS BASES;
• ADENINE pairs with THYMINE
A T
• GUANINE pairs with CTYOSINE G C
• These pairs are linked by weak hydrogen bonds.
• ONE sugar + ONE PHOSPHATE + ONE BASE
= A NUCLEOTIDE.
• Many nucleotides = one gene
• Thousands of genes may occur on one DNA
(chromosome) strand.
• The DNA is twisted
into a double helix
1
A SINGLE
NUCLEOTIDE
and a base
joined
Consists
of
a
ajoined
Phosphate
toSugar
to the side
These three
molecules are
bonded in a special
way to form the
units of the DNA
molecule called
NUCLEOTIDES
2
In the DNA
molecule,
nucleotides link
together to form
long chains called
polynucleotide
chains. (poly=many)
3
There are four
different bases.
The sugar and
phosphates are the
same throughout the
DNA molecule but …
4
The four bases are either
single or doubled ringed
A single ringed
base
A double ringed
base
5
There are two types of single ringed bases
T
Thymine
C
Cytosine
6
There are two types of double ringed bases
A
Adenine
G
Guanine
7
Four different nucleotides therefore
occur in the DNA molecule
T
A
C
G
8
C
The
polynucleotide
chain now with
the four
different bases
A
T
G
9
The
sugar
The DNA
and
molecule
phosphates
consists of
form
the
TWO
chains
backbone
10
It is arranged
What
do you
in the
notice
about
opposite
the second
direction
to
the chain?
first chain
11
?
But how are
the bases
arranged to
link the two
chains?
?
?
?
12
When bases combine ..
A two ringed base
always links to
a one ringed
base
13
Adenine
Thymine
A
T
Guanine
Guanine
always joins
to Cytosine
G
Adenine
always joins
to Thymine
Cytosine
C
14
G
C
A
T
T
A
C
G
Now look at
how the bases
link with each
other to join
the two
chains of the
DNA molecule
1
• The DNA molecule has many
nucleotides
•To see this clearly we need to
simplify a nucleotide
Base
Sugar
A
Phosphate
2
T
A
G
A
C
T
T
A
G
C
T
A
A
T
C
T
G
A
A
T
C
G
A
T
Try to
determine
which
nucleotide will
link to the form
the second DNA
chain
Remember
Which
nucleotide
A
joins
toto
T A
and
will
link
?
G to C
3
Interlinking
bases
As the bases
link to each
other, the DNA
molecule is
twisted into a
double helix
Two SugarPhosphate
backbones
4
DNA replication
How DNA is copied
5
DNA replication
When a cell
divides, the DNA
needs to be
copied so that
each new cell has
the same DNA as
the parent cell
6
DNA replication
An enzyme
New strands breaks the
hydrogen
form
The two chains
bonds
complimentary
separate
to parent strands linking the
two chains
7
T
A
G
A
C
T
T
A
G
C
T
A
A
T
C
T
G
A
A
T
C
G
A
T
A closer view of
DNA replication
looking at part
of a strand
An enzyme unzips
the DNA molecule
8
T
A
G
A
C
T
T
A
G
C
T
A
A
T
C
T
G
A
A
T
C
G
A
T
DNA
Strands
separate
9
T
A
G
A
C
T
T
A
G
C
T
A
A
T
C
T
G
A
A
T
C
G
A
T
T
A
G
A
C
T
T
A
G
C
T
A
A
T
C
T
G
A
A
T
C
G
A
T
Free
Nucleotides
link to
form new
chains and
two
identical
DNA
molecules
DNA REPLICATION
• The weak hydrogen bonds holding the
complementary base pairs together break
as a result of enzyme action.
• Two single strands now result.
• Each single strand picks up free
nucleotides from the nucleotide pool in the
nucleoplasm and becomes double again.
• Since Thymine can only combine with
Adenine, and Guanine with Cytosine, the
two new double strands are identical to
each other as well as to the original strand.
e drawing below summarises the functions of the nucleotides:
D.N.A
R.N.A
D.N.A.
mR.N.A.
tR.N.A.
Proteins
DNA
RNA
1 Double helix
2 Adenine (A),
Thymine (T),
Cytosine (C) &
Guanine (G) are
the nitrogenous
bases
1
3 Can REPLICATE itself
3
4 Deoxyribose sugar
5 Found in nucleus
4
6 Has hydrogen
bonds
6
Single strand
2
Adenine, Cytosine
Guanine
Uracil (instead of
Thymine)
5
Does not replicate
Ribose sugar
Found in nucleus and
cytoplasm
Single strand
Protein Synthesis
How DNA directs how proteins are made
1
The variety of
life on earth is
due to different
proteins.
2
Protein Synthesis
You are different
from the people
around you because
your proteins are
different.
3
Protein Synthesis
Your hair, muscles
fibres in your skin
are all made of
proteins.
4
Protein Synthesis
If you have
straight hair, your
protein is slightly
different to
someone who has
curly hair
5
Protein Synthesis
• Proteins are made up of units called
amino acids
• In our examples we will use a few
amino acids to represent a protein
• Proteins are much larger and have
more that 50 amino acids
6
Protein Synthesis
Proteins are made up of units called
amino acids.
Amino acids join together to make
proteins.
7
Protein Synthesis
Proteins differ from each other by the type
(different shapes) and sequence (the order in
which the shapes occur) of amino acids.
If this is the
protein for
straight hair
A single amino
acid change
results in curly
hair
8
Protein Synthesis
The proteins are different because the
DNA for curly and straight hair is
different.
There is a THREE letter DNA code
(codon) for each amino acid.
Eg. TGG codes for
9
Protein Synthesis
In this example:
TAC codes for a
AGC codes for a
AAA codes for a
GGT codes for a
The code for this amino
acid sequence is :
AAA GGT GGT
What is the DNA code
for this sequence?
TAC AGC GGT
10
Protein Synthesis: Overview of the Process
DNA
G
A
C
T
T
A
G
C
T
A
C
T
G
A
A
T
C
G
A
T
RNA
makes
C
U
G
A
A
U
C
G
A
U
Protein
makes
11
Protein Synthesis: A closer look
Firstly, part of the
DNA is copied into
messenger RNA
(mRNA)
This is called
TRANSCRIPTION
12
Protein Synthesis: A closer look
The mRNA carries
the message to
make the protein to
the cytoplasm and
attaches to the
ribosome
13
Protein Synthesis: A closer look
tRNA collects amino
acids in the cytoplasm
14
Protein Synthesis: A closer look
TRANSLATION: tRNA
brings amino acids to
the ribosome which
link and form proteins
Protein Synthesis
The Detailed Process
1
TRANSCRIPTION
A piece of DNA that codes for a
protein is copied into mRNA
2
Part of the
DNA
molecule is
unzipped by
an enzyme
T
R
A
N
S
C
R
I
P
T
I
O
N
3
DNA
separates
T
R
A
N
S
C
R
I
P
T
I
O
N
4
T
A
C
A
A
A
A
G
C
G
G
T
A
U
G
U
U
U
U
C
G
C
C
A
A piece of
DNA from
one side is
copied into
mRNA
T
R
A
N
S
C
R
I
P
T
I
O
N
5
T
A
C
A
A
A
A
G
C
G
G
T
mRNA
separates
from DNA
A
U
G
U
U
U A U G U U U U C G C C A
U
C
G
C
C
A
T
R
A
N
S
C
R
I
P
T
I
O
N
6
T
A
C
A
A
A
A
G
C
G
G
T
A U G U U U U C G C C A
7
T
A
C
A
A
A
A
G
C
G
G
T
mRNA moves
out of the
nucleus to a
ribosome in
the cytoplasm
A U G U U U U C G C C A
ribosome
8
mRNA attaches to a ribosome
G C C AA U G U U U U C G C C A
9
TRANSLATION
The ribosome encodes
mRNA to form a new
protein
10
tRNA brings a specific
amino acid which links
mRNA
Amino
Acid
tRNA
U A C
A U G U U U U C G C C A
mRNA
11
The tRNA with its specific
amino links to mRNA
according to its specific
three letter code
Amino
Acid
tRNA
U A C
A U G U U U U C G C C A
mRNA three letter
Corresponding
tRNAcode
code(codon)
(anticodon)
mRNA
12
tRNA
The
tRNA
ribosome
brings
moves
inmoves
into
the
The
amino
next
the
along
cytoplasm
amino
the acids
mRNA
acidto
combine
molecule
according
collect
another
exposing
to the
next
the
amino
mRNA
next acid
codon
codon
U A C A A A
A U G U U U U C G C C A
13
tRNAs bring in another amino acids to extend
the protein chain
A A A
A G C
A U G U U U U C G C C A
The process continues as the ribosome moves along
mRNA exposing the next codon
14
tRNAs bring in another amino acids to extend
the protein chain
A G C G G U
A U G U U U U C G C C A
The process continues as the ribosome moves along
mRNA exposing the next codon
15
TERMINATION: Ribosome and mRNA
separate
NEW “Protein” is formed
G G U
A U G U U U U C G C C A
16
In Summary …
DNA
T A C A A A A G C G G T
makes
RNA
makes
Protein
A U G U U U U C G C C A
Transcription
Translation