9. Chromosomes
B- Chromosome Number:
1-Diploid chromosome number: is the number of
chromosome in somatic cell (2N) in human =
23pairs
2-Haploid chromosome number: is the number of
chromosome in gametes (from eggs, sperm ) cell
(1N) in human = 23single
10. Eukaryotic Cell Cycle
• The eukaryotic cell cycle consists of two basic
stages: Interphase and mitosis.
Interphase:
is the phase of the cell cycle
in which the cell spends the
majority of its time
Preparing for cell division
Interphase =20 h
Mitosis =1 h
11. Cell division: Mitosis
• Mitosis for proliferation of somatic cell.
• Mitosis results in:
division in the nucleus to produce two nuclei has
the same type and numbers of chromosomes .
• Mitosis is divided into four stages:
prophase, metaphase, anaphase, and telophase.
12. Nuclear envelope disappears
Chromosome along the equator
of the cell
Nucleoli and
formation of cell plate
formation of two Nucleoli as
same number and type of
chromosome
13. Cytokinesis and cleavage
• Cytokinesis follows mitosis, and it is the
last stage of the cell cycle.
• Cytokinesis divides the entire cell into two
new cells.
• Cytokinesis plant cell
• Cleavage + Cytokinesis animal cell
14. Steps of root tip squash method
1-Growing onions and wait it for root growth and then
treated it by 2ml Carnoy fixative or alchohol
70% for 24 h.
2- Using scissors , cut 2 roots tips about 1cm long and
transfer them into a test tube
3- Fill the tube about 2-3ml with 1NHCL and cover
the tube by gauze then tie it with rubber
4- Place the tube in 60 °C water bath and incubate
for 5 min.
5- Remove the tube from water bath
15. Steps of root tip squash method
6- remove the HCL from the test tube and rinse the
roots in the water about 3 times
7- cover the root with the aceto carmine stain and
incubate the root in the stain for 12 min.
8- Transfer a root to the slide
9- using a razor blade cut off most of the unstained
part of the root and discard it
10-Cover the root tip by a cover slip then press down
formally with one fingerfor flattening the sample
16. Steps of root tip squash method
11- put one more drop of stain and leave it for 1min
then rinse it and cover the root tip by a cover slip
12-Examine under the microscope at low power and
high power
Prokaryotic cells:Pro = “before”, karyon = “nucleus”are primarily distinguished by the fact that they lack a membrane-bound nucleus. In fact, the only membrane in prokaryotic cells is the plasma membrane--the outer boundary of the cell itself. Their genetic material is naked within the cytoplasm (do not have nuclear envelope).ribosomes their only type of organelle (do not have organelles such as mitochondria and Golgi apparatus).Eukaryotic cells:Eu = “true”, karyon = “nucleus”The most noticeable feature that differentiates these more complex cells from prokaryotes is the presence of a nucleus, a double membrane-bound control center separating the genetic material, DNA (deoxyribonucleic acid), from the rest of the cell.In addition to the plasma membrane, eukaryotic cells contain internal membrane-bound structures called organelles.
*The plant cell has microtubules instead of centrioles, which is responsible for spindle fibers formation.*الخلايا النباتية لا تحتوي على الجسم المركزي ولكنها تحتوي على أنيبيبات دقيقة حرة في السيتوبلازم وهي المسؤولة عن تكوين خيوط المغزل أثناء انقسام الخلايا النباتية
Nucleus structure:1-The nuclear envelope surrounds the nucleus and all of its contents.2-There are pores and spaces for RNA and proteins to pass through while the nuclear envelope keeps all of the chromatin and nucleolus inside.3-Nuclear sap.4-Chromatin is made of DNA. DNAis the nucleic acids inside of the cell. When the cell is going to divide, the chromatin becomes very compact. It condenses. When the chromatin comes together, you can see the chromosomes.5- You will also find the nucleolus inside of the nucleus. When you look through a microscope, it looks like a nucleus inside of the nucleus. Itproduces ribosome that needed for protein synthesis
Central dogma:The genetic information in DNA is transcribed in the nucleus to RNA, which is then transported to the cytoplasm where it is translated into various proteins. The types of RNA that are translated into proteins are known as messenger RNA (mRNA).
Each chromosome is made up of DNA tightly coiled many times around proteins called histones that support its structure.Each chromosome has a constriction point called the centromere, which divides the chromosome into two sections, or “arms.” The short arm of the chromosome is labeled the “p arm.” The long arm of the chromosome is labeled the “q arm.” The location of the centromere on each chromosome gives the chromosome its characteristic shape, and can be used to help describe the location of specific genes.*Chromosomes are not visible in the cell’s nucleus—not even under a microscope—when the cell is not dividing. However, the DNA that makes up chromosomes becomes more tightly packed during cell division and is then visible under a microscope. Most of what researchers know about chromosomes was learned by observing chromosomes during cell division.
Cells spend the majority of their time in Interphase, which consists of three stages called Gap 1 (G1), Synthesis (or S), and Gap 2 (G2). In the G1 phase, the cell is growing and replicating cytoplasmic organelles.DNA is synthesized during S phase so that two exact copies of the chromosomes are produced. During the G2 phase cells are preparing for division. This involves the supercoiling and winding of DNA to ‘package’ it into chromosomes.The mitosis phase (M) and consists of mitosis and cytokinesis, where two genetically identical daughter cells are formed.
During prophase DNA is packaged into very tightly wound chromosomes. At this time, each chromosome consists of two identical arms, called sister Chromatids and the nuclear envelope is broken down into vesicles.During metaphase the chromosomes line up along the equatorial plate. and plays an important role in the correct distribution of chromosomes and other cell material.At this point, each chromosome has at least two microtubules attached to it – one from each pole of the cell. During anaphase, the two sister chromatids of each chromosome separate and move to opposite poles of the cell. In telophase, the chromatids reach opposite poles of the cell, the nuclear envelopes reform around each set of chromatids, and the chromatids themselves become less condensed.
The details of cytokinesis vary among different kinds of organisms. For example, animal cells, divide by a constriction of their cell membrane. This constriction is called a cleavage, and it forms in the same plane as the metaphase equatorial plate. In contrast organisms such as plants have cell walls and undergo cytokinesis a bit differently. In these organisms, vesicles from the Golgi apparatus migrate to the plane of cell division and fuse to form a cell plate. This plate will become the new cell membranes and cell walls that separate the two daughter cells.
