Download Year 12 Genetics

Year 12
Genetics
Structure and function of
DNA, RNA and proteins
DNA polymer
 The
shape of DNA is a double helix (a
twisted ladder)
 It is a very large molecule but cannot be
seen with the naked eye unless it is
condensed and in the form of a
chromosome.
 A chromosome is chromatin coiled up in a
specific pattern
 Chromatin is DNA wrapped around
HISTONE proteins.
Structure of a
chromosome
 Made
of
chromatin
Structure of
Chromatin
 Made
of DNA
wrapped around
HISTONES
DNA Monomers
A
long polymer molecule of DNA is made
of building blocks (monomers) called
Nucleotides.
 DNA stands for Deoxyribose Nucleic Acid,
deoxyribose is in reference to the sugar
which is contained in each nucleotide.
 Sugars and phosphates chemically
bonded alternately make up the sides of
the DNA ladder, attached from each
sugar is a nitrogenous base.
 A sugar unit, phosphate unit and a base
attached together constitute a
nucleotide.
Sugar
Phosphate
Nucleotide
Nitrogenous bases
Nucleotide
Guanine
More
Chemical
detail for
those
interested in
the atoms
that make
up the
phosphate,
sugar and
base in a
nucleotide
Nitrogenous bases
 Each
of the four bases (Adenine, Thymine,
Cytosine and Guanine) in a DNA
molecule is different in it’s chemical
composition.
 Adenine and Guanine are larger
molecules which are double ringed
structures they are called PURINES
 Thymine and Cytosine are smaller with
only one ring to their structure and they
are called PYRIMIDINES
 A always pairs with T
 C always pairs with G
RNA
 Stands
for RiboNucleic Acid
 Three main differences between DNA and
RNA is
1) RNA is always single stranded
2) Has URACIL instead of THYMINE as a
nitrogenous base, all others are the same
3) RNA’s sugar in each nucleotide has an
extra oxygen molecule.
DNA
Deoxyribose means
one less oxygen.
RNA
The point of DNA
 The
sequence of bases along the DNA
molecule is important as it holds the
instructions for how to create proteins,
through a process called transcription
and translation.
 Examples of proteins: haemoglobin,
receptors on the surface of cells to
receive chemicals, hormones, structural
proteins in cells, mucus, clotting factors,
enzymes, actin and myosin found in
muscle cells, and the list goes on.
The point of RNA
 DNA
holds the instructions but it is RNA
that allows the instructions to be correctly
read and also to co-ordinate the creation
of the proteins from the DNA code.
 There are three types of RNA
1)
2)
3)
mRNA – messenger RNA
tRNA – transfer RNA
rRNA – ribosomal RNA
mRNA
 Involved
in transcription
 Takes a copy of the code from the
nucleus to the cytoplasm of the cell
tRNA
 Involved
in translation
 Allows each
sequence of 3 bases
to be decoded into a
sequence of amino
acids, it has a special
and specific shape to
enable the
connection of amino
acids.
rRNA
 Involved
in translation
 Made of two subunits
 Facilitates the reading of the DNA code
along mRNA and conversion into a series
of bonded amino acids using tRNA.
Many
ribosomes
can
translate
the mRNA
at the
same time,
creating
large
quantities
of a protein
quickly.
A closer look at proteins
A
functional unit within a cell, can provide
structure, shape, movement, receiving of
signals and transmission of signals.
 Can be all manner of shapes and sizes.
 The linear order of amino acids in each
protein determines its three-dimensional
structure and activity.
Protein complexes