chromosome,control of gene expression,recombinent DNA technoogy

1. CHROMOSOMES
© The Human Genome Project:
Biocomputing Admin Ed Yung

2. Chromosomes in eukaryotes and
prokaryotes are different
PROKARYOTES EUKARYOTES
single chromosome plus plasmids many chromosomes
circular chromosome linear chromosomes
made only of DNA made of chromatin, a
nucleoprotein (DNA coiled
around histone proteins)
found in cytoplasm found in a nucleus
copies its chromosome and divides
immediately afterwards
copies chromosomes, then the
cell grows, then goes through
mitosis to organise
chromosomes in two equal
groups
© 2007 Paul Billiet ODWS

3. Chromosomes
in eukaryotes
 Found in the nucleus
 Condensed and visible during cell division
 At the beginning of mitosis they can be
seen to consist of two threads (sister
chromatids) joined by a centromere
 The sister chromatids are identical copies
 During mitosis the sister chromatids
separate and are placed into two nuclei
© 2007 Paul Billiet ODWS
Image believed to be in the Public Domain

4. Mouse
Maize

5. Organism Chromosome
numbers
Human 46
Chimpanzee 48
House Mouse 40
Maize 20
© 2007 Paul Billiet ODWS

6. Human chromosomes
Image believed to be in the Public Domain

7. A prokaryotic chromosome consists of a single molecule of DNA in the
form of a closed loop. The chromosome is described as circular.
A prokaryotic cell has only one chromosome.
A eukaryotic chromosome is linear, not circular, in other words it has
two ends, like a sausage. Each chromosome contains one molecule of
DNA for the first half or so of interphase, then the DNA replicates, and
the two DNA molecules remain together (as sister-chromatids) in the
same chromosome for the rest of interphase. This does not happen in
prokaryotic cells.
Eukaryotic cells have more than one chromosome.
A further difference: prokaryotic chromosomes consist only of a naked
DNA molecule, but eukaryotic chromosomes also contain many
molecules of proteins (mostly histones). The DNA is wound around
these proteins.

8. romosome as circular DNA. Usually the entire genome is a single circle, but often there are extra circles called plasmids. The
Bacterial Chromosome Structure
Prokaryotic cells (bacteria) contain
their chromosome as circular DNA.
Usually the entire genome is a single
circle, but often there are extra
circles called plasmids. The DNA is
packaged by DNA-binding proteins.

9. The bacterial DNA is packaged in loops back and forth.
The bundled DNA is called the nucleoid. It concentrates
the DNA in part of the cell, but it is not separated by a
nuclear membrane (as in eukaryotes.) The DNA does form
loops back and forth to a protein core, attached to the
cell wall.

10. 10
Eukaryotic Chromosome
Structure
 Eukaryotic DNA is packaged into
chromatin.
 Chromatin structure is directly
related to the control of gene
expression.
 Chromatin structure begins with the
organization of the DNA into
nucleosomes.
 Nucleosomes may block RNA
polymerase II from gaining access

11. 11
Eukaryotic Chromosome
Structure
 Methylation (the addition of –CH3) of
DNA or histone proteins is associated with
the control of gene expression.
 Clusters of methylated cytosine
nucleotides bind to a protein that prevents
activators from binding to DNA.
 Methylated histone proteins are
associated with inactive regions of
chromatin.

12. Control of Gene Expression

13. What is the gene expression?
 Is the process by which information
from a gene is used in the synthesis of
a functional gene product (proteins)
The process of gene expression is used
by all known life - eukaryotes ,
prokaryotes , and viruses - to
generate the macromolecular
machinery for life.

15. Steps in gene expression
 (1) Transcription
(mRNA synthesis),
 (2) Post-transcriptional
process (RNA splicing),
 (3) Translation (protein
synthesis)
(4) post-translational
modification of a
protein.

16. 16
Control of Gene Expression
 Controlling gene expression is often
accomplished by controlling
transcription initiation.
 Regulatory proteins bind to DNA
to either block or stimulate
transcription, depending on how
they interact with RNA polymerase.

17. 17
Control of Gene Expression
 Prokaryotic organisms regulate
gene expression in response to their
environment.
 Eukaryotic cells regulate gene
expression to maintain
homeostasis in the organism.

18. 18
Regulatory Proteins
 Gene expression is often controlled
by regulatory proteins binding to
specific DNA sequences.
 regulatory proteins gain access to the
bases of DNA at the major groove
 regulatory proteins possess DNA-
binding motifs

19. 19
Prokaryotic Regulation
 Control of transcription initiation
can be:
 positive control – increases
transcription when activators bind
DNA
 negative control – reduces
transcription when repressors bind to
DNA regulatory regions called
operators

20. 20
Prokaryotic Regulation
 Prokaryotic cells often respond to
their environment by changes in
gene expression.
 Genes involved in the same
metabolic pathway are organized in
operons.
 Some operons are induced when
the metabolic pathway is needed.
 Some operons are repressed when
the metabolic pathway is no longer
needed.

21. 21
Prokaryotic Regulation
 The lac operon contains genes for
the use of lactose as an energy
source.
 Regulatory regions of the operon
include the CAP binding site,
promoter, and the operator.
 The coding region contains genes
for 3 enzymes:
 β-galactosidase, permease, and
transacetylase

22. 22

23. 23
Prokaryotic Regulation
 The lac operon is negatively
regulated by a repressor protein:
 lac repressor binds to the operator to
block transcription
 in the presence of lactose, an inducer
molecule binds to the repressor protein
 repressor can no longer bind to
operator
 transcription proceeds

24. 24
Eukaryotic Regulation
 Controlling the expression of
eukaryotic genes requires
transcription factors.
 General transcription factors are
required for transcription
initiationrequired for proper binding
of RNA polymerase to the
DNAspecific transcription factors
increase transcription in certain
cells or in response to signals

25. 25

26. 26
Eukaryotic Transcription
 General transcription factors bind to
the promoter region of the gene.
 RNA polymerase II then binds to
the promoter to begin transcription
at the start site (+1).
 Enhancers are DNA sequences to
which specific transcription factors
(activators) bind to increase the
rate of transcription.

27. 27

28. 28
Posttranscriptional Regulation
 Control of gene expression usually
involves the control of transcription
initiation.
 But gene expression can be controlled
after transcription, with mechanisms such
as:
 RNA interference
 alternative splicing
 RNA editing
 mRNA degradation

29. 29
Posttranscriptional Regulation
 RNA interference involves the use
of small RNA molecules
 The enzyme Dicer chops double
stranded RNA into small pieces of
RNA
 micro-RNAs bind to complementary
RNA to prevent translation
 small interfering RNAs degrade
particular mRNAs before translation

30. 30

31. What is DNA?
DNA= Deoxyribu-Nucelic Acid
 DNA is a very large
molecule, made up of
smaller units called
nucleotides
 Each nucleotide has three
parts: a sugar (ribose), a
phosphate molecule, and a
nitrogenous base.
 The nitrogenous base is the
part of the nucleotide that
carries genetic information

32. What is gene?
• A gene is a stretch of DNA
that codes for a type of
protein that has a function
in the organism.
• It is a unit of heredity in a
living organism.. All living
things depend on genes
• Genes hold the information
to build and maintain an
organism's cells and pass
genetic traits to offspring.

33. What are gene components?
 Genes contain:
EXONS: a set of coding regions…
INTRONS: Non-coding regions removed
sequence and are therefore labeled
split genes (splicing).

34. What is the genome?
 The genetic
complement of
an organism,
including all of
its GENES, as
represented in
its DNA

35. Steps in gene expression
 (1) Transcription
(mRNA synthesis),
 (2) Post-transcriptional
process (RNA splicing),
 (3) Translation (protein
synthesis)
(4) post-translational
modification of a
protein.

36. What are the genetic changes?
 An alteration in a segment
of DNA, which can disturb
a gene's behavior and
sometimes leads to
disease.
 It may be:
 (1) Small genetic change,
genetic drift (mutation)
 (2) large genetic change,
genetic shift

37. Recombinant DNA
technology

38. What is recombination?
 The exchange of
corresponding DNA
segments between
adjacent
chromosomes during
the special type of
cell division that
results in the
production of new
genetic make up...

39. Recombinant DNA
technology
In vitro recombination
Genetic engineering
Genetic surgery

40. In genetic engineering, recombination can
also refer to artificial and deliberate
recombination of pieces of DNA, from
different organisms, creating what is
called recombinant DNA.

42. Application of genetic
engineering in
Medicine
(1) Treatment of
genetic diseases
(gene therapy)
 e.g. SCID girl

43. (2) Production of
medically useful
biologicals (e.g.
insulin)
Recombinant Human Growth
Hormone
Recombinant insulin (Humulin)

44. (3) Vaccines production
 Firstly, the gene in a
pathogenic virus that
stimulates protective immunity
should be identified.
 That portion of DNA is then
isolated and incorporated into
an established harmless virus
(e.g. vaccinia virus).

45.  This new recombinant
virus is used as a vaccine.
 These vaccines are much
safer since they do not
expose the patients to the
actual virus and do not
risk to infection.
 This method may be
useful in vaccines against
malaria and
schistosomiasis and many

46. (4) Pharmacogenomics
Deals with the
influence of genetic
variation on drug
response in patients
by correlating gene
expression with a
drug's efficacy or
toxicity

47. Design drugs
adapted to an
individual's
genetic make-
up