ميكروبيولوجي للمهن الصحية

1. MICROBIOLOGY
for the Health Sciences
‫أ. فريد ابو العمرين‬
CHAPTER: 6
1

2. Section III.
Chemical and Genetic Aspects of
Microorganisms
Chapter 6. Biochemistry: The Chemistry
of Life
2

3. Chapter 6 Outline
• Introduction
• Organic Chemistry
–
Carbon Bonds
–
Cyclic Compounds
• Biochemistry
–
–
Lipids
–
3
Carbohydrates
Proteins
–
Nucleic Acids
Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins

4. Nucleic Acids
Function
•
DNA and RNA comprise the 4th major group of biomolecules in
living cells after (Carbohydrates, Lipids, Proteins) .
•
DNA and RNA are critical to proper functioning of a cell.
1.
2.
•
Deoxyribonucleic Acid
Ribonucleic Acid
DNA is the “hereditary molecule” – the molecule that contains
the genes and genetic code.
–
Information in DNA must flow to the rest of the cell for the
cell to function properly – the flow is accomplished by RNA.
•
4
RNA molecules participate in the conversion of the genetic code
into proteins and other gene products.

5. Nucleic Acids
Structure
• In addition to the elements C, H, O, and N, DNA and
RNA also contain phosphorus, P.
• The building blocks of nucleic acid polymers are called
nucleotides.
•
•
5
The building blocks of DNA are called DNA nucleotides.
The building blocks of RNA are called RNA nucleotides.

6. Nucleotides

Two nucleotides, each consisting of:
1. a nitrogenous base (A G C T)
 adenine (A), guanine (G), thymine (T), cytosine (C) and uracil
2. a five-carbon sugar (S)
 Deoxyribose, Ribose
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3. a phosphate group (P)

7. 7

8. The Pyrimidines and Purines Found in
DNA and RNA.
A and G are purines;
T, C and U are
pyrimidines.
Thymine is found
in DNA but not in
RNA. Uracil is
found in RNA, but
not in DNA. The
other 3 bases are
found in both.
8

9. Base pairs that occur in double
stranded DNA molecules.

Note that A and T are
connected by two hydrogen
bonds, whereas G and C are
connected by three hydrogen
bonds.

The arrows represent the
points at which the bases are
bonded to deoxyribose
molecules.
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10. Types of RNA
• There are 3 types of RNA, named for their function:
–
–
–
10
Messenger RNA (mRNA)
Ribosomal RNA (rRNA)
Transfer RNA (tRNA)

11. DNA Structure
• For a double-stranded DNA molecule to form, the
nitrogenous bases on the two separate strands must
bond together.
• The bonding forces of the double-stranded polymer
cause it to assume the shape of a double alpha-helix,
similar to a right-handed spiral staircase.
11

12. A section of a nucleic acid polymer.
12
Within a double stranded DNA molecule, A in one strand always
bonds with T in the complimentary strand, and G in one strand
always bonds with C in the complimentary strand.
A–T and G–C are known as base pairs.

13. Double-stranded DNA
molecule, also known
as a double helix.
13

14. DNA Replication
• When a cell is preparing to divide, all DNA molecules in the
chromosomes of the cell must duplicate, thereby ensuring
that the same genetic information is passed on to both
daughter cells.
–
This is called DNA replication.
• DNA replication occurs by separation of the 2 DNA strands
and the building of complementary strands by the addition
of the correct DNA nucleotides.
• The most important enzyme required for DNA replication is
the DNA polymerase.
14

15. DNA Replication.
15

16. DNA Replication
Gene Expression
• A gene is a particular segment of a DNA molecule or
chromosome.
• It is the sequence of the four nitrogenous bases of
DNA (i.e., A, G, C, and T) that spell out the
instructions for a particular gene product.
• Although most genes code for proteins, some code
for rRNA and tRNA.
• Some genes code for more than one gene product.
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17. The Central Dogma
• The Central Dogma explains the flow of genetic
information within a cell.
• DNA
–
mRNA
protein.
One gene of a DNA molecule is used to make one molecule
of mRNA by a process known as transcription.
–
The genetic information in the mRNA is then used to make
one protein by a process known as translation.
17

18. DNA Replication
Gene Expression, cont.
• All genes on a chromosome are not being expressed
at any given time. It would not be logical for a cell to
produce a particular enzyme if it was not needed.
–
Genes that are only expressed when the gene products are
needed are called inducible genes.
–
Genes that are expressed at all times are called
constitutive genes.
• The process by which the genetic code within the DNA
molecule is transcribed to produce an mRNA molecule is
called transcription.
18
–
The primary enzyme involved is RNA polymerase.

19. Transcription
• In eucaryotes, transcription occurs within the nucleus;
the newly formed mRNA molecules then travel through
the pores of the nuclear membrane into the cytoplasm,
where they are used to produce proteins.
• In procaryotes, transcription occurs in the cytoplasm;
ribosomes attach to the mRNA molecules as they are
being transcribed at the DNA – thus both transcription
and translation may occur simultaneously.
19

20. 20

21. Translation
• The process of translating the message carried by
mRNA, whereby particular tRNAs bring amino acids to
be bound together in the proper sequence to make a
protein, is called translation.
• The base sequence of the mRNA molecule is read in
groups of 3 bases, called codons.
• The 3-base sequence codon can be read by a
complementary 3-base sequence (the anticodon) on a
tRNA molecule.
21

22. Chart to illustrate the sequence of 3 bases (GGC) in the DNA template
that codes for a particular codon (CCG) in mRNA, which in turn,
attracts a particular anticodon (GGC) on the tRNA carrying an amino
acid (proline).
DNA
tRNA
Amino
Template
(Codon)
(Anticodon)
Acid
G
C
G
G
C
G
C
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mRNA
G
C
Proline

23. Translation
 For example, the tRNA with the anticodon base
sequence UUU carries the amino acid lysine to
the mRNA codon AAA.
 Similarly, the mRNA codon CCG codes for the
tRNA anticodon GGC, which carries the amino
acid proline.
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24. Translation (protein synthesis).
24

25. Mutation
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26. Mutation

If one of the bases of a DNA gene is incorrect or out of sequence
(known as a mutation).



Mutations (involve changes in the base sequences of genes)

Such errors are the basis for most genetic and inherited diseases,
such as phenylketonuria (PKU), sickle cell anemia, cystic fibrosis,
cleft lip, extra fingers, albinism.

Likewise, nonpathogenic microbes may mutate to become
pathogens, and pathogens may lose the ability to cause disease by
mutation.
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The amino acid sequence of the gene product will be incorrect.
For example, some diabetics a mutation in one of their
chromosomes caused a rearrangement of the bases in the gene
that codes for insulin.