1. Chromosome, Genome and Cell Cycle
Dr.Aida Fadhel Biawi
2013

2. - Chromosomes are used as a way of referring to the genetic basis of an organism as either diploid or haploid. Many eukaryotic cells have two sets of the chromosomes and are called diploid. Other cells that only contain one set of the chromosomes are called haploid.

3. A diploid cell has two sets of each of its chromosomes
A human has 46 chromosomes (2n = 46)
In a cell in which DNA synthesis has occurred all the chromosomes are duplicated and thus each consists of two identical sister chromatids
Maternal set of
chromosomes (n = 3)
Paternal set of
2n = 6
Two sister chromatids
of one replicated
chromosome
Two nonsister
chromatids in
a homologous pair
Pair of homologous
chromosomes
(one from each set)
Centromere

4. Chromosome Duplication
In preparation for cell division, DNA is replicated and the chromosomes condense
Each duplicated chromosome has two sister chromatids, which separate during cell division
0.5 µm
Chromosome duplication (including DNA synthesis)
Centromere
Separation of sister chromatids
Sister chromatids
Centrometers
An eukaryotic cell has multiple chromosomes, one of which is represented here. Before duplication, each chromosome has a single DNA molecule.
Once duplicated, a chromosome consists of two sister chromatids connected at the centromere. Each chromatid contains a copy of the DNA molecule.
Mechanical processes separate the sister chromatids into two chromosomes and distribute them to two daughter cells.

5. Non-sister chromatids Two duplicated chromosomes
Chromosome Duplication
Because of duplication, each condensed chromosome consists of 2 identical chromatids joined by a centromere.
Each duplicated chromosome contains 2 identical DNA molecules (unless a mutation occurred), one in each chromatid:
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Two unduplicated
chromosomes
Centromere
Sister
chromatids
Duplication
Non-sister chromatids
Two duplicated chromosomes

6. Structure of Chromosomes
The centromere is a constricted region of the chromosome containing a specific DNA sequence, to which bind 2 discs of protein called kinetochores.
Kinetochores serve as points of attachment for microtubules that move the chromosomes during cell division..
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Metaphase chromosome
Kinetochore
microtubules
Centromere
region of
chromosome
Sister Chromatids

7. Chromosome structure
p: short arm
q: long arm
C: constriction point or centromere , the location of centromere give the chromosome its shape and can be used to help describe the location of the genes.

8. A typical mitotic chromosome at metaphase

9. Diploid - A cell possessing two copies of each chromosome (human body cells).
Homologous chromosomes are made up of sister chromatids joined at the centromere.
Haploid - A cell possessing a single copy of each chromosome (human sex cells).

10. Genome The genome is all the DNA in a cell.
All the DNA on all the chromosomes
Specifically, it is all the DNA in an organelle.
Eukaryotes can have 2-3 genomes
Nuclear genome
Mitochondrial genome
Plastid genome
If not specified, “genome” usually refers to the nuclear genome.

11. A gene is a molecular unit of heredity of a living organism
A gene is a molecular unit of heredity of a living organism. It is widely accepted by the scientific community defined as a some stretches of deoxyribonucleic acids DNA that code for a polypeptide or for an RNA chain that has a function in the organism.

12. Human genome 22 autosome pairs + 2 sex chromosomes
3 billion base pairs in the haploid genome

13. Components of the human Genome
About 20% codes for proteins
About 80 percent of the nucleotide bases in the human genome may be transcribed. but transcription does not necessarily imply function , Elizabeth (2007).

14. What is the function of the remaining DNA ?

15. Much DNA in large genomes is non-coding
Complex genomes have roughly 10x to 30x more DNA than is required to encode all the RNAs or proteins in the organism.
The non-coding DNA include:
Intones in genes
Regulatory elements of genes
Pseudogenes
Intergenic sequences
Interspersed repeats
Tandem repeats
Telomeres

16. An intron is any nucleotide sequence within a gene that is removed by RNA splicing while the final mature RNA product of a gene is being generated .

17. Regulatory sequence is a segment of a nucleic acid molecule which is capable of increasing or decreasing the expression of specific genes within an organism. Regulation of gene expression is an essential feature of all living organisms

18. Pseudogenes are dysfunctional of genes that have lost their protein-coding ability or are otherwise no longer expressed in the cell .Pseudogenes often result from the accumulation of multiple mutations within a gene whose product is not required for the survival of the organism.

19. An Intergenic region) is a stretch of DNA sequences located between genes . Intergenic regions are a subset of Noncoding DNA
. Occasionally some intergenic DNA acts to control genes nearby, but most of it has no currently known function.
It is one of the DNA sequences sometimes referred to as junk DNA, also known as "dark matter"

20. Interspersed repetitive DNA is found in all eukaryotic genomes
Interspersed repetitive DNA is found in all eukaryotic genomes. Certain classes of these sequences propagate themselves by RNA mediated transposition, they have been called retrotransposons, and they constitute 25–40% of most mammalian genomes. Interspersed repetitive DNA elements allow new genes to evolve.

21. Tandem repeats :copies of DNA which lie adjacent to each other
Tandem repeats :copies of DNA which lie adjacent to each other. There are three types :
1- Satellite DNA - typically found in centromeres and heterochromatin

22. 2- Minisatellite - repeat units from about 10 to 60 base pairs, found in many places in the genome, including the centromeres

23. 3- Microsatellite - repeat units of less than 10 base pairs; this includes telomeres, which typically have 6 to 8 base pair repeat units

24. - Telomeres are regions of repetitive DNA at the end of a chromosome, which provide protection from chromosomal degradation during DNA replication.

25. Telomeres and Aging: Is there a connection?

26. Telomeres are…
- Repetitive DNA sequences at the ends of all human chromosomes
- They contain thousands of repeats of the six-nucleotide sequence, TTAGGG
-In humans there are 46 chromosomes and thus 92 telomeres (one at each end)

27. What do telomeres do? - They protect the chromosomes.
- They separate one chromosome from another in the DNA sequence
(Without telomeres, the ends of the chromosomes would be fused , leading to chromosome fusion and massive genomic instability).

29. Telomere function
1- Telomeres are also thought to be the "clock" that regulates how many times an individual cell can divide. Telomeric sequences shorten each time the DNA replicates.

31. Think of it like this….
2- Telomeres effectively "cap" the end of a chromosome in a manner similar to the way the plastic on the ends of our shoelaces "caps" and protects the shoelaces from unraveling.

32. How are telomeres linked to aging?
Once the telomere shrinks to a certain level, the cell can no longer divide. Its metabolism slows down, it ages, and dies.

33. It has been proposed that telomere shortening may be a molecular clock mechanism that counts the number of times a cell has divided and when telomeres are short, cellular senescence (growth arrest) occurs.

34. Cell Cycle in Prokaryotic and Eukaryotic

35. The Prokaryotic Cell Cycle
1- The prokaryotic cell cycle is a relatively straightforward process. Essentially, unicellular prokaryotic organisms grow until reaching a critical size, and synthesize more cytoplasm, cell membrane, ribosomes, cell wall, and other cell constituents. They then replicate their DNA, segregate copies of the chromosome, and divide by a process called binary fission to produce two new genetically identical daughter cells.

36. Binary fission in prokaryotic

37. 1- The bacterium before binary fission is when the DNA tightly coiled.
Binary fission in a prokaryotic
1- The bacterium before binary fission is when the DNA tightly coiled.
2- The DNA of the bacterium has replicated.
3- The DNA is pulled to the separate poles of the bacterium as it increases size to prepare for splitting.
4- The growth of a new cell wall begins to separate the bacterium.
5- The new cell wall fully develops, resulting in the complete split of the bacterium.
6- The new daughter cells have tightly coiled DNA, ribosomes, and plasmids

38. 2- Most research suggests that the rate of fission in prokaryotic organisms is largely controlled by environmental conditions. For example, most prokaryotic organisms have an optimum temperature range for cell growth. When environmental temperatures are above or below the optimum, cell division tends to decrease.

39. 3-Under ideal environmental conditions, many prokaryotic species undergo binary fission at a fairly rapid rate with generation times of one to several hours. This can lead to an astonishing growth in population size over a relatively short period of time. In some instances, populations of prokaryotes may increase by a million or even a billion fold in a matter of days.

40. The Eukaryotic Cell Cycle

41. Phases of the Cell Cycle
Interphase
G1 - primary growth
S - genome replicated
G2 - secondary growth
M - mitosis
C - cytokinesis

43. Cell cycle begins with the formation of two cells from the division of a parent cell and ends when the daughter cell does so as well.
Observable under the microscope, M phase consists of two events, mitosis (division of the nucleus) and cytokinesis (division of the cytoplasm).
As replication of the DNA occurs during S-phase, when condensation of the chromatin occurs two copies of each chromosome remain attached at the centromere to form sister chromatids.
After the nuclear envelope fragments, the microtubules of the mitotic spindle separate the sister chromatids and move them to opposite ends of the cell.
Cytokinesis and reformation of the nuclear membranes occur to complete the cell division.

44. -Most of the time, cells are in interphase, where growth occurs and cellular components are made. DNA is manufactured during S phase.
-To prepare the cell for S phase (DNA synthesis), G1 phase occurs (the preparation of DNA synthesis machinery, production of histones).
-In an analogous manner, the cell prepares for mitosis in the G2 phase by producing the machinery required for cell division.
-The length of time spent in G1 is variable. In growing mammalian cells often spend 8-10 hours in G1 phase. G2 is usually shorter than G1 and is usually 4-6 hours. (brief …..)

45. Interphase G1 - Cells undergo majority of growth
S - Each chromosome replicates (Synthesizes) to produce sister chromatids
Attached at centromere
Contains attachment site (kinetochore)
G2 - Chromosomes condense - Assemble machinery for division such as centrioles

46. DNA duplication during interphase
Mitosis
Some diploid cells divide by mitosis.
Each new cell receives one copy of every chromosome that was present in the original cell.
Produces 2 new cells that are both genetically identical to the original cell.
DNA duplication during interphase
Mitosis
Diploid Cell