Download DNA: The material of heredity

DNA: The material of heredity
Structure of DNA
 DNA
(deoxyribonucleic acid) was discovered
in 1869.
 In
the 1950s, scientists showed that DNA is the
material responsible for heredity.
 In
1953, James Watson and Francis Crick used
the information collected by scientists on DNA
to build a 3D model.
From using this picture, this is what we
can say about the structure of DNA:
The DNA molecule is twisted into a
spiral called a helix. This twisted
ladder shape is called a double helix.
 Each DNA molecule is made up of
two very long chains of smaller units
called nucleotides. DNA’s two chains
are connected by crosspieces, or
rungs, that give the molecule a
ladder-like appearance.

From using this picture, this is what we
can say about the structure of DNA:
 Each
nucleotide in a DNA
molecule is made up of three
parts:
1.)
sugar molecule
2.)
phosphate group
3.)
nitrogen base
Draw a picture to represent a
nucleotide:
Nitrogenous bases

Four different nitrogen bases are found in the
nucleotides of DNA (they are the letters of the
genetic alphabet):
 1.)
adenine (A)
 2.)
guanine (G)
 3.)
cytosine (C)
 4.)
thymine (T)
Two major functions of DNA
 It
undergoes duplication, which is
also called replication (it makes a
copy of itself).
 It
directs protein synthesis.
Base pairing rules
 Nucleotides
are bonded together in
a specific way to form the double
helix (they form the rungs of the
ladder).
 A always bonds with T
 C always bonds with G
Bonding of nucleotides
 The
sides of DNA are formed by
bonding the sugar of one nucleotide
to the phosphate of the next
nucleotide in a continuous chain.
 Draw a picture below to represent
this (see next slide).
DNA replication
 Replication
is the making of an exact
copy of a DNA molecule, which
begins when the two chains of a
DNA molecule begin to separate.
Steps in replication
 1.)
The nitrogen-base pairs are pulled
apart, which can be compared to
the unzipping of a zipper.
 Draw
a picture. (see next slide)
Steps in replication
 2.)
Nucleotides (A, C, G, T) that are
in the nucleus of a cell bond to the
nitrogen bases flowing the rule A
bonds with T, and C bonds with G.
 Draw
a picture (see next slide)
Steps in replication
 3.)
Each side of the original DNA has
produced a new DNA molecule,
which is identical to the original
molecule.
Accuracy and repair

DNA replication occurs with a high degree of
accuracy, but some errors occur. Even one error can
have a serious effect

A mutation is a change in the nucleotide sequence.

The number of errors is reduced as many enzymes
proofread DNA and make repairs.

DNA can be damaged by a variety of agents,
including chemicals and UV radiation from the sun.
Proteins synthesis
The DNA in the chromosomes of an organism has a
different sequence of nitrogen-base pairs. This is why we
are all different and unique.
 The individual genes of a DNA molecule contain
instructions for making specific proteins.
 Making proteins is extremely important, since many parts
of an organism are made of proteins. Proteins called
enzymes help our bodies to carry out its life processes by
speeding up chemical reactions.

The genetic code
 The
language in which the instructions for proteins
are written in DNA is called the genetic code.
 The
language uses the nitrogen bases A, T, C, and G.
 Proteins
 The
are made up of amino acids.
string of code words in a gene causes many
amino acids to come together in a certain order to
make a particular protein.
RNA (ribonucleic acid)
 Similar
in structure to DNA, but also has some
differences.
 Single
chain of nucleotides (DNA is a double
chain).
 Instead
of thymine, RNA has a nitrogenous base
called uracil.
C
bonds with G
A
bonds with U (not T) (but T still bonds to A)
RNA (ribonucleic acid)
 RNA
copies the information for making a
protein from DNA.
 The
process by which genetic
information is copied from DNA to RNA is
called transcription.
Draw a picture of transcription
mRNA and transcription
 Messenger
RNA (mRNA) carries the proteinmaking instructions from the DNA in the nucleus
to a ribosome in the cytoplasm, which is where
proteins will be made.
 Nitrogen
bases on mRNA molecules code for
certain amino acids; the nitrogen bases are
read in groups of three that are called codons.
Draw a picture of codons
Translation

Transfer RNA (tRNA) carries a particular amino acid to
the mRNA, which is determined by the codon.

The amino acids are joined together by chemical bonds
to form a protein.

The process of assembling polypeptides from information
encoded in mRNA is called translation.

Draw a picture of translation