Download Ch 1 - Composition of cells, DNA

The Nucleic
Acids
An Introduction
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DNA
An Introduction
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What does DNA stand for?
De oxy-ribose
Type of
monosaccharide
Nucleic
Found in the
nucleus
(eukaryote) or
nucleoid
(prokaryote) of
cells
Acid
As in acids
and bases
DNA can also be written as Deoxyribonucleic Acid
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Where do you find DNA?
All mature cells contain DNA except the red blood cells
DNA is found in the nucleus
Small amounts of DNA are also present in the
chloroplasts and mitochondria
Chloroplast
Nucleus
Mitochondrion
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Source: http://www.tokyo-med.ac.jp/genet/picts/cell-e.jpg
Building blocks

A single unit of DNA is called a
nucleotide it is made up of:
A Sugar Molecule (Deoxy-ribose)
 A Phosphate molecule
 A Nitrogenous Base

P
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P
Building blocks

P
P
P

The nucleotides are
bound together via
covalent bonds
between the
phosphate groups,
forming a strand of
DNA
These covalent
bonds are very
strong and difficult
to break
P
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DNA
DNA is made up of 2 strands.
The strands are held together by weak bonds
between the nitrogen bases
The bonding between the strands is so weak that
the two strands will easily separate at 100˚C
There are four types of nitrogen bases:
Cytosine (C), Guanine (G), Adenine (A) and Thymine (T)
What pairs with C?
What pairs with A?
http://academy.d20.co.edu/kadets/lundberg/dnapic2.html
http://www.tokyo-med.ac.jp/genet/picts/dna.jpg
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DNA
Once the 2 strands of DNA are bound together,
the strands coil to form a helical shape
This is why DNA is often called a double helix
In this diagram, the 2 DNA strands have
backbones that are shown in blue and red
The nitrogen bases are shown in yellow
http://academy.d20.co.edu/kadets/lundberg/dnapic2.html
http://www.tokyo-med.ac.jp/genet/picts/dna.jpg
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The Gene Code


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The order of the nitrogenous bases A,
T, G & C is very important.
The sequence provides cells with
templates for the production of every
protein in the body
These proteins play many different
roles in the body
Each segment of DNA which
determines the structure of one protein
is called a gene
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The DNA in the
nucleus of your cells
is tightly wound up
to form
chromosomes so as
to take up less space
and avoid being
tangled
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Chromosomes

Each chromosome
carries
approximately
30,000 genes
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RNA
An Introduction
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What does RNA stand for?
Ribose
Type of
monosaccharide
Nucleic
Acid
Found in the
nucleus or
nucleoid of cells
As in acids
and bases
RNA can also be written as Ribonucleic Acid
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Building blocks

Like DNA, a single unit of RNA is called
a nucleotide. It is made up of:
A Sugar Molecule (Ribose)
 A Phosphate molecule
 A Nitrogenous Base


Notice that the sugar molecule in RNA is
different than in DNA
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RNA
There are 2 other major differences in the make up of
RNA compared with DNA:
• RNA is made up of only 1 strand of nucleotides
• In RNA, the four types of nitrogenous bases are:
Cytosine (C), Guanine (G), Adenine (A) and Uracil (U)
•Note that RNA does not contain the base thymine but
contains uracil instead.
So in RNA:
• Cytosine pairs with Guanine
• Adenine pairs with Uracil
http://academy.d20.co.edu/kadets/lundberg/dnapic2.html
http://www.tokyo-med.ac.jp/genet/picts/dna.jpg 16
RNA

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
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There are 3 different types of RNA:
Messenger RNA (mRNA) – copies and carries
the genetic code from the DNA in the nucleus
to the ribosomes
Ribosomal RNA (rRNA) – makes up
ribosomes which are responsible for
assembling the proteins according to the
instructions on mRNA
Transfer RNA (tRNA) – molecules which
carry the amino acids to the ribosomes
where they are used to construct the protein
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Where do you find RNA?
All mature cells contain RNA
RNA is found in the nucleus as messenger RNA
In the ribosomes as ribosomal RNA
In the cytoplasm as transfer RNA and messenger RNA
Ribosomes
Nucleus
Cytoplasm
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Source: http://www.tokyo-med.ac.jp/genet/picts/cell-e.jpg
Protein Production
1. Transcription:
DNA code on genes
copied to mRNA
template
2. mRNA is able to
pass through
nuclear pores and
travel to ribosomes
3. Translation:
Amino acids are
carried to the
ribosomes by tRNA
where they are
assembled into a
polypeptide chain
according to the
mRNA sequence 19
Protein Modification
4. Bending and
folding: The
polypeptide is then
able to enter the
RER where it is
folded, bended and
further modified.
Small parts of RER
containing the
protein then pinch
off, forming vesicles
which then travel to
the Golgi Body
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Protein Export
5. Finishing touches:
In the Golgi body, the
protein may be
further modified
6. Export: Part of the
Golgi body containing
the finished product
will then pinch off,
forming a vesicle which
is transported to the
cell membrane where it
fuses with the
membrane and expels
its contents outside the
cell. This is called
exocytosis.
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Summary
DNA
RNA
Double Stranded,
helical
Single stranded, 3
different forms –
mRNA, rRNA, rRNA
Nucleotides: C, G, A, T Nucleotides: C, G, A, U
Sugar: Deoxyribose
Sugar: Ribose
Function: Carries code Function: Assembles
for protein production proteins using DNA
code
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