Lesson 1 Biology PDF

Lesson 1. The inherited material of human’s cells Subject of Lesson 1: To know 1. Structural and functional features of nuclear and extranuclear inherited material of human cells. 2. Levels of DNA packing (nucleosome, 30-nm fiber and 300-nm loops, interphase and metaphase chro...

Lesson 1. The inherited material of human’s cells Subject of Lesson 1: To know 1. Structural and functional features of nuclear and extranuclear inherited material of human cells. 2. Levels of DNA packing (nucleosome, 30-nm fiber and 300-nm loops, interphase and metaphase chromosomes). 3. Description of metaphase chromosomes. Karyotypic analysis. The substantiation of subject. Knowledge about structural features of interphase and metaphase human’s chromosomes is necessary for understanding the patterns of heredity and variability, for cytogenetic diagnostics of chromosome diseases. Besides, knowledge about karyotype, human idiogram and sex chromatin is necessary by study the pathogenesis and diagnostics of inherited diseases. Task 1. Structure of eukaryotic cell. (we`ll discuss it during ZOOM) Eukaryotic cell includes a lot of organoids. There are: mitochondria, rough and smooth endoplasmic reticulum, lysosomes, Golgi apparatus, centrioles, ribosomes. In plant cell we can observe also plastids, including chloroplasts. The cell nucleus is a remarkable organelle (Fig.1.). It functions to: 1. Store genes on chromosomes. 2. Organize genes into chromosomes to allow cell division. 3. Transport regulatory factors and gene products via nuclear pores. 4. Produce mRNA that code for proteins 5. Produce ribosomes in the nucleolus. 6. Organize the uncoiling of DNA to replicate key genes. Study the main structures of nucleus (Table 1.) and most important their functions.  Table 1. Main components of nucleus. Component Structure and function Nuclear membrane Consists of two membranes and is penetrated by pores. Through these pores exchange of different substances between nucleus and (nucleolemma) cytoplasm occurs. Separates transcription, proceeded in nucleus, from translation of protein in cytoplasm. There is complex of DNA (40%) and protein (60%): Chromatin 1. Euchromatin – sites of interphase chromosomes, decondensed as much as possible. (interphase 2. Heterochromatin – sites of chromosomes, which are always in chromosome) condensed state. Nuclear sap Chromatin and nucleolus are placed inside it. It contains ions, proteins (including enzymes) and nucleotides. The (karyoplasm) process of mRNA, tRNA and rRNA maturation takes place here. It contains a lot of DNA, rRNA and proteins. It is formed by sites of nucleolar organizer regions of some Nucleolus chromosomes (13th, 14th, 15th, 21st, 22nd) with genes of rRNA. In nucleolus the synthesis of rRNA and ribosomal subunits occurs. Fig.1. Internal structure of nucleus  Task 2. The nuclear and extranuclear inherited material of the human cells. According to works of A. Weissman and T. Morgan, majority of inherited material is placed in chromosomes of nucleus. In this case we can speak about nuclear inheritance. However, genetic experimental results showed that cytoplasm can participate in inherited information transmission too. Cytoplasmic inheritance is provided by genes, which are localized out of nucleus. Main part of such genes is placed in mitochondria. Mitochondria have some of their own DNA (Fig.2.), ribosomes, tRNA and can make many of their own proteins. The DNA is circular and lies in the matrix in structures called “nucleoids”. Each nucleoid may Fig.2. Mitochondrial DNA contain 4-5 copies of the mitochondrial DNA (mtDNA). Human mitochondrial DNA encodes a number of mitochondrial proteins and participates in synthesis of some important enzymes. In mammals, 99.99% of mitochondrial DNA is inherited from the mother. This is because the spermatozoon carries its mitochondria around of its tail and has only about 100 mitochondria compared to 100.000 in the oocyte. As the cells develop, more and more of the mtDNA from males is diluted out. Hence less than 0.01% of the mtDNA is paternal. This means that mutations of mtDNA can be passed from mother to child. Mutations in mtDNA do cause diseases. As expected, those tissues or organs most likely to be affected would be the ones most dependent on oxidative phosphorylation (ATP production). In young persons it might not be picked up because even a person with 15% normal mitochondria might have enough to be healthy. However, aging patients may show a more severe disease phenotype. Some example of diseases: 1. Leber’s hereditary optic neuropathy (degeneration of the optic nerve, accompanied by increasing blindness): caused by mutation to the gene encoding subunit 4 of the NADH-C0Q reductase. 2. “Ragged muscle fibers” associated with jerky movements is caused by mutation of mitochondrial lysine tRNA. 3. Kaerns-Sayre syndrome: eye defects, abnormal heartbeat, central nervous system degeneration is caused by several large deletions in mtDNA. Study the comparative characteristic of the nuclear and extranuclear inherited material of the human cells (Table 2.). Draw attention on features of mitochondrial DNA. Why only mitochondria have DNA except nucleus? Table 2. Inherited material of the human cells Nuclear (chromosomal) material Extranuclear (mitochondrial) material 23 pairs of chromosomes (46, XX; 46, XY) In one chromosome – 1 DNA molecule In one mitochondria – 4-6 circular “naked” with proteins 6 ft long DNA molecules Quantity of nucleotides pairs per Quantity of nucleotides pairs in one DNA – haploid number – 3.5 billion 16.569 Quantity of genes – 150 thousands. All There are 2 genes of rRNA; 22 genes of proteins of cytoplasm and 90% of tRNA; 13 genes of tissue respiration mitochondrial proteins; tRNA and enzymes; genes of 10% of mitochondria rRNA. proteins. Provides nuclear inheritance. Provides cytoplasmic inheritance. The inheritance of genes obeys the The inheritance of genes doesn’t obey the Mendel’s laws. Mendel’s laws. Task 3. Levels of DNA packaging. Study and draw the scheme of DNA packaging (Fig.3). Note: DNA, histones, nucleosome (“beads on a string”), solenoid (30-nm fiber), loops, condensed loops, chromosome. Chromosome DNA Histones Nucleosome Fig. 3. Levels of DNA packaging Solenoid loops Condensed loops Answer the following questions: 1. How many times DNA is shorten thanks to nucleosomal organization of chromosome? DNA is shortened 5 times by nucleosomal organization. 2. What importance for eukaryotic cells has DNA packaging? DNA packaging allows the extremely long DNA molecules ro fit inside the nucleus, to allow for efficient storage and organization of genetic information within the cell, and also plays a crucial role in regulating gene expression by conrolling access to different DNA regions depending on how tightly packed the chromatin is.  Task 4. Interphase chromosomes. Interphase takes main part of cell cycle, during it most gene expression occurs. This last action can take place only in decondensed chromosomes. Because of that interphase chromosome is present as chromatin. (euchromatin) There are two types of chromatin: euchromatin and heterochromatin. Euchromatin is a type of decondensed chromatin that is rich in gene concentration and genetically active. This type of chromatin generally appears as light-colored bands when stained in GTG banding and observed under optical microscope. Heterochromatin is a type of chromatin that is darkly staining and tightly packaged throughout the cell cycle and is genetically inactive. There are two types of heterochromatin: constitutive and facultative. Constitutive heterochromatin is fixed and irreversible in form and function. Constitutive heterochromatin tends to occur around the centromere and in telomeres of chromosome. There are also heterochromatin regions in arms of 1 st, 9th, 16th chromosomes and Y-chromosome contains regions of constitutive heterochromatin. In the q arm!! Facultative heterochromatin has the ability to return to the euchromatic state. The inactive X-chromosome (Barr body) is made up of facultative heterochromatin. Some facultative heterochromatin is thought to be inactivated by being attached to the nuclear envelope. Besides, we can distinct so-called sex-chromatin (Fig. 4.). There are X- chromatin and Y-chromatin. X-chromatin (Barr body) is a mass of condensed sex chromatin in the nuclei of normal female somatic cells due to inactive one of the two X chromosomes. Inactivation occurs around the 16 th day of embryonic development. Y-chromatin is a brilliantly fluorescent body (heterochromatin region in q-arm of Y chromosome) seen under the microscope in cells containing a Y chromosome when the cells are stained with the dye quinacrine. X-chromatin is observed more often in mucous of buccal cavity and leucocytes, skin fibroblasts, hair bulb cells. Answer the following questions: 1. In what status one of female X-chromosomes in somatic cells during interphase is? Inactive 2. How it is look by light microscope in the stained preparations? What is a name of this cytological structure? Itenvelope? appears as dark-colored bands when stained in GTG banding and observed under a microscope; nucelar chromatin? 3. In what status of male Y-chromosomes in somatic cells during interphase is? Active 4. Is it possible to discover Y-chromosome in male somatic cells during interphase by proper staining of preparation? What is a name of this cytological structure? Yes. The Y chromosome is brillianty fluorescent when stained with quinacrine. Cytological structure?  Fig. 4. Types of sex-chromatin Task 5. Structure and functions of metaphase chromosome. Study (Table 3.) structural and functional features of different metaphase chromosome parts. Table 3. Sites of metaphase chromosome Chromosome site Structural and functional features It is present in each chromosome and is made of heterochromatin. Centromere divides chromosome into two Primary arms. constriction There is kinetochore on the centromere region of chromosome. (centromere) Kinetochore – it is a complex of proteins that forms at the centromere and helps to separate the sister chromatids during anaphase of mitosis. Depending on the position of the centromere, the chromosomes may have P- (short) arm or Q- (long) arm and are divided into three types. Metacentric - where the centromere is in the middle Arms (p = q). Submetacentric - where the centromere is displaced from the centre (p < q). Acrocentric - where the centromere is at one end (p Histones > nucleosome > solenoid loops > condensed loops > chromosomes. 4. DNA helps with the efficient storage and organization of genetic material. It also helps with regulating gene expression in cells by controlling aceess to different gene region depending on how tightly packed the chromatid is. 5. Chromatin is a condensed form of DNA that consists of proteins, it forms chromosomes. 6. Euchromatin is the active form of chromatin that is rich in gene concentration. It appears as light-coloured bands when stained in GTG banding, and observed under a microscope. 7. Constituve heterochromatin is the condensed form of chromatin that is fixed and irreversible. It occurs around the centromere and telomere and is unable to active. It typically occurs in the arms of chromosomes 1, 9, 16 and the Y chromosome. 8. Facultatice heterochromatin is a decondensed form of chromatin that has the ability to return to a euchromatic state. Barr bodies are made up of facultative heterochromatin.