13.3
Lesson objectives :
- Explain DNA
in terms of its
structure and
function
-Explain RNA in
terms of its
structure and
function
DNA vs. RNA
 Chromosomes are made of proteins and deoxyribonucleic acid or
DNA ( an organism`s genetic material )
 A gene : a segment ( section ) of DNA on a chromosome .
 Cells are composed of millions of molecules .
 These molecules need countless number of directions to be formed
.
 All these needed information , directions are contained in DNA.
Carries the genes that provides all the
information , or directions ,needed for
making all the proteins a cell requires to :
1- grow
2-maintain itself
3-reproduce
97 % of your DNA on your chromosomes
does not form genes .
Segments of DNA that are not parts of genes
are called junk DNA .
 Strands of DNA in a chromosome are tightly coiled like a telephone
cord or a coiled spring .
 Or it is like a twisted zipper ( this shape is called a double helix ) fig
13 page 505
 Why is this shape important ?
 The coiling allows more genes to fit in a small space.
Critical thinking
 A molecule
made of a nitrogen base , a sugar , and a phosphate group
Sides of DNA zipper
Teeth of zipper
Sugar phosphate groups
Nitrogen bases
Q 6 PAGE 512
Four nitrogen bases :
- Adenine A
- Cytosine C
-Thymine T
-Guanine G
- A AND T always bond together
- C AND G always bond together
 * takes place before cell division ( interphase ) , so all daughter cells
will carry the same genetic information . Q 10 PAGE 512
 * IT IS : the process of copying a DNA molecule to make another
identical one.
Fig 14 page 540
BEFORE
REPLICATION
ONE COPY OF DNA
AFTER
REPLICATION
TWO COPIES OF DNA
DNA : DeoxyriboNucleic Acid
RNA : DeoxyriboNucleic Acid
 Proteins are made with the help of ribonucleic acid (RNA )
 RNA : a type of nucleic acid that:
Q3 PAGE 511
1- carries the code for making proteins from the nucleus to
the cytoplasm.
2- carries amino acids around inside a cell
3- forms a part of ribosomes .
DNA
RNA
Both are made up of nucleotides
strands
Double-stranded
Single –stranded
Nitrogen bases A,G,C, T
A,G,C,U (Uracil)
Type of sugar
function
Deoxyribose sugar
Ribose sugar
Stores the information for Carries out the
protein synthesis
instructions
encoded in DNA
EXIT TICKET
Lesson objectives :
- Types of RNA
- explain the role
of RNA in protein
production
RNA
A
1
DNA
B
2
 1- to make ( m RNA ) from DNA
: ( Transcription )
Now m RNA moves to the cytoplasm (messenger )
It is used as a template to synthesis protein
 2- t ( RNA ) carries amino acids to the ribosome
A complete protein is a folded chain of amino acids .
3- r RNA helps to form chemical bonds to attach amino acids
together. (protein )
 The process of making a protein from RNA .
 Occurs in Ribosomes .
 Ribosomes : cell organelles that are attached to the rough endoplasmic reticulum
or in the cell`s cytoplasm .
EXIT TICKET
Lesson objectives :
- WHAT IS A
MUTATION
- TYPES OF
MUTATIONS
 A mutation : A change in the nucleotide sequence of agene
(changes in the sequence of nitrogen base pairs )
 These mistakes (changes )can happen during replication .
 Mutations van be triggered ( excited )by exposure to X- ray
, ultraviolet light , radioactive materials , and some kinds of
chemicals .
1- This can cause the mutated gene
protein than the normal one
to code for a different
2-Some mutated genes do not code for any protein
As a result the cell will lose the ability to make one of the proteins
it needs .
4- some mutations in human DNA cause genetic disorders . (
depends on location , have a look on table 4 page 544 ).
How ever some mutations don`t affect proteins ( don`t affect traits ) ,
and some may benefit the organism .
EXIT TICKET
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