Cell Nucleus PDF - Ajman University

Ajman University College of Dentistry Histology & Cell Biology BDS105 Dr. Al-Moutassem Billah Khair The Nuclear Cell Biology N U C L E U S  NUCLEUS N The nucleus is an essential part of protoplasm, present U in almost all living ce...

Ajman University College of Dentistry Histology & Cell Biology BDS105 Dr. Al-Moutassem Billah Khair The Nuclear Cell Biology N U C L E U S  NUCLEUS N The nucleus is an essential part of protoplasm, present U in almost all living cells of animals and plants C (Eukaryotes). A notable exception is the human erythrocyte, which lacks a nucleus. L *The nucleus is a spherical or ovoid body with a diameter E of roughly 1-3 μm and it’s location depends on the cell type (central, peripheral, basal, superficial). U *A cell may contain more than one nucleus. It is derived S from a mother cell by cell division (mitosis or meiosis). It contains the structures controlling there production and functioning of the cell; these are DNA.  NUCLEUS N The nucleus contains, in addition to the DNA (DNA is less U than 20% of nucleus mass) also a large quantity of proteins C called nucleoproteins (DNA-binding proteins & nuclear matrix proteins) and some RNA (newly synthesized m, t, L rRNA). E The nucleus contains the entire human karyotype, which consists of 46 chromosomes. Chromosomes are discrete U collections of genes and nuclear proteins. Genes determine S most of an organism’s characteristics, but not all genes are located on nuclear chromosomes (e.g. mitochondria have a separate genome that encodes some functions).  NUCLEUS N U The nucleus structure C *Nuclear Envelope L **Nuclear Pores E ***Chromatin ****Chromosomes U *****Nucleolus S  The nuclear envelope E The nuclear envelope separates the entire of the nucleus from cytoplasm. It consists of two layers of plasma N membrane (each layer of standard phospholipid bilayer structure), which represent a specialized part of the V endoplasmic reticulum. E The nuclear envelope is 7-8 nm thick and contains several hundred nuclear pores. L The outer membrane often is continuous with the O membrane of the RER, and is studded with ribosomes. The P intermembranous space is continuous with that of the endoplasmic reticulum and like much of it. On the inner E aspect of the envelope there is a fibrous lamina bound to membrane proteins and linked with condensed peripheral chromatin. This structure does not block nuclear pores. E N V E L O P E E N V E L O P E P O R E  The nuclear pores P The nuclear pores are openings in nuclear envelope, at the margins of which the inner and outer nuclear membranes become continuous. They allow large O macromolecules synthesized in the nucleus to pass into the cytoplasm and vice versa. Nuclear pores are annuli with 60 nm diameter and R each annulus consists of eight peripheral subunits with large dense body in the center. The pores not open all times but are bridged by a diaphragm of protein. E The number of nuclear pores is depending on physiological state of nucleus, and it is increased with the increasing of nucleus activity. That is mean they are not stable structures and they are in dynamic state. P O R E P O R E  C Chromatin H Except during cell division, the chromosomes, each R make up a separate length of the DNA complement, exist in a complicated strands. Chromatin is composed mainly O of coiled strands of DNA bound to basic proteins. The M chromatin basic unit is nucleosome, which consists of a core of four types of histones surrounded by DNA. Two A types of chromatin can be seen with light and electron T microscopes: I. Heterochromatin tends to be clumped around the periphery of the I nucleus but also forms irregular clumps throughout the nucleus. It represents that DNA which is not active in RNA synthesis. N II. Euchromatin forms the electron-lucent nuclear material. It represents that DNA which is active in RNA synthesis.  C Chromatin H R O M A T I N  C Chromatin H R O M A T I N  C Chromatin H R O M A T I N  C Chromosomes H Chromosomes are flexible rod-like structures that R become visible during nuclear division when the chromatin of the cell nucleus reverts to the condensed O state. Each species of plant and animal has a constant M number of chromosomes. The chromosomes in different O species of organisms differ in shape as well as in number. The set of chromosomes included in diploid cells called S karyotype. O In human cells, there are 46 chromosomes comprising 23 homologous pairs, the members of each pair having the M same length of DNA and coding for the same proteins. E  C H R O M O S O M E  C H R O M O S O M E  C Chromosomes The human karyotype contains 22 pairs of H autosomes and a pair of sex chromosomes. The female R karyotype contains a pair of identical X sex chromosomes (homomorphic), while the male karyotype O contains a pair of morphological different sex M chromosomes designated X & Y (heteromorphic). One of X chromosomes in female consists of heterochromatin O and is located near the nuclear envelope. This S chromosome is known as Barr body, which can be used to determine the sex and some chromosomal O abnormalities. M Each member of a homologous pair of mitotic chromosome is identical in length, centromere location E and banding pattern.  C Chromosomes H R O M O S O M E  C Chromosomes These pairs are classified by Deniver system according to their length H and centromere position in eight groups: 1. Group A: three pairs of the largest metacentric chromosomes (1-3). R 2. Group B: two pairs of large submetacentric chromosomes (4-5). O 3. Group C: seven pairs of medium-sized metacentric chromosomes (6-12). M 4. Group D: three pairs of medium-sized acrocentric chromosomes (13-15). O 5. Group E: three smaller pairs (16-18), 16 is metacentric, while 17 & S 18 are submetacentric. 6. Group F: two pairs of short metacentric chromosomes (19-20). O 7. Group G: two pairs of small acrocentric chromosomes (21-22). M 8. Group H: includes in female two medium submetacentric X chromosomes, while in male a medium submetacentric X E chromosome and a very small acrocentric Y chromosome.  C Chromosomes H R O M O S O M E  N The nucleolus U Nucleolus is a dense heterogeneous structure, C prominent during interphase, disappear during L metaphase, reappear during telophase. This structure consists of nucleolar organizer region (DNA for rRNA E transcription), fibrillar region (primary rRNA) and O granular region (ribosome subunits). Heterochromatin is attached to the nucleolus but its function unknown. L The nucleoli especially are found in embryonic cells, U in cells highly active in protein synthesis, and in rapidly S growing malignant tumors. They are the sites of ribosomal RNA synthesis and ribosomes assembly.  N U C L E O L U S  N U C L E O L U S