What is the class molecular biology about?

Answer 1

This course class writeen by Dr. Yasser babair (PSMCHS) Dahran, Saudi Arabia introduction to DNA and RNA extraction then you should to explain the most important of molecular biology techniqes such as Alkaline Lysis and agarose gel electroporesis

INTRODUCTION TO MOLECULAR BIOLOGY

CELL:

- The basic unit of all living organisms which can reproduce itself exactly (mitosis).

- Each cell is bounded by a cell membrane of lipids & proteins, which control the passage of substances in & out of the cell.

- Cells contain the cytoplasm which contains a nucleus & other structures (organelles) specialized to carry out particular activities in the cell.

- Two types of cells exist: (1) Prokaryotes (pro: before, karyon: nucleus) which are single-celled organs that contain a single cellular strand of DNA & possess few of the internal structures.

(2) Eukaryotes (eu: true, karyon: nucleus) are more complex single- celled organisms that originate from prokaryotes.

- Eukaryotic cells contain DNA within a nucleus which is a membrane-bound structure.

- Complex organisms e.g. Man is built up of millions of cells that are especially adapted to carry out particular functions. The process of cell differentiation begins early in the embryo & the cells of a particular type (e.g. blood cells, liver cells) always give cells of the same type.

- Each cell has a particular number of chromosomes in its nucleus.

- The sex cells (sperm & ova) always contain half the number of chromosomes of all the other cells of the body.

- At fertilization sperm & ovum combine to form a cell with a complete set of chromosomes that will develop into the embryo.

Cell body:

- The enlarged portion of the nerve cell (neurone) for example contains the nucleus.

- It is mainly concerned with the cell nutrition.

STRUCTURE (EUKARYOTIC CELL):

- Eukaryotic cells consist of two basic compartments: the nucleus & the cytoplasm.

- The nuclear compartment is the control center of the cell because it contains the genetic information that regulates the structure & function of the cell.

- It is surrounded by a double membrane called the nuclear envelope.

- The cytoplasmic compartment lies between the plasma membrane which is the outermost structure of the cytoplasm.

The structure & function of the plasma membrane:

- The plasma membrane is the outermost bounding of the cell that consists of lipids, proteins & small amounts of carbohydrate.

- The membrane ensures the structural integrity of the cell, regulates the flow of materials into & out of the cell & participates in cellular communication & cellular identification.

- Because it is mostly lipid, the membrane is a natural barrier to water-soluble molecules; lipid-soluble materials pass through it with ease.

Structure & function of organelles:

- The nucleus is one of the most important cellular organelles. Other organelles include the mitochondria, endoplasmic reticulum, Golgi complex, lysosomes (secretory vesicles), flagella (long whip-like structures & cilia (small extensions).

- It houses the DNA, which contains the genetic information that determines the structure & function of the cell.

- The nucleus is bound by the nuclear envelope that contains numerous pores, which allow many materials (but nest the DNA) to pass freely between the nucleus & the cytoplasm.

- The mitochondrion has two membranes, an outer one & an inner one. The inner membrane is thrown into folds called cristae.

- Cellular energy production (by break down of glucose takes place, partly in the cytoplasm but mostly in the mitochondrion.

- The endoplasmic reticulum is a network of membrane channels in the cytoplasm & is the main location of cellular protein synthesis.

- It is either smooth endoplasmic reticulum (SER) or rough endoplasmic reticulum.

- The SER has no ribosomes & produces phospholipids (needed to make more plasma membrane). & has many additional functions in different cells.

- The RER contains many ribosomes on its outer surface & is involved in synthesizing protein for extra cellular use (e.g. for hormones) & in production of enzymes that are contained in lysosomes.

- Proteins produced on the surface of the RER are transferred to the Golgi complex where they are sorted chemically & repackaged into lysosomes.

- The flagellum (on the human sperm cell) is a long whip-like structure, which can be utilized as a kind of motive force in the cell.

- Cilia, with numerous small extensions, prop fluids & materials along their surfaces.

- Both cilia & flagella contain nine pairs of microtubules arranged in a circle around a central pair.

Energy & metabolism:

- Energy in the cell is produced mainly by breakdown of glucose & carbohydrates which take place partly in the cytoplasm but mostly in the mitochondria.

- Complete breakdown of glucose is called cellular respiration & consist of four parts: Glycolysis, the transmission reaction, the citric acid cycle & the electron transport system.

Fermentation:

- Fermentation is a chemical reaction in which pyruvate is converted into lactic acid or some other product such as ethyl alcohol.

- It occurs in the absence of oxygen & at this point cells must rely on glycolysis & fermentation to generate energy & it is of three types:

1. Lactic acid fermentation is an important source of food made from milk & selected bacteria.

2. Alcoholic fermentation produces ethanol from pyruvate & occurs in certain microorganisms.

3. Alcoholic drinks & hard liquor are all produced by combining plant by-products (grains & fruits) with microorganisms that are alcoholic fermenters.

The cell cycle:

- It is the life cycle of the cell, a process which is the basis of reproduction & growth & therefore essential for all forms of life.

- The cell cycle consists of two phases; interphase & cell division.

Interphase:

- A period of active cellular synthesis occurring between cell division & is divided into three phases G1 (gap1), S (synthesis), G2 (gap2).

- During interphase, the cell replicates its organelles & molecules needed by the two daughter cells, i.e. synthesis & growth occurs in preparation for cell division.

Cell division:

- Reproduction of the cells by division of the chromosomes (karyokinesis) & then of the cytoplasm (cytokinesis).

- Cell division to produce more body (somatic) cells is by mitosis & cell division during the formation of gametes is by meiosis.

- The cytoplasm is a semi-fluid material that consists of many molecules, including water, protein, ions, nutrients, vitamins dissolved in gases & waste products.

- It forms a nutrient pool from which the cell draws chemicals it needs for metabolism & is also dumping ground for waste.

- The cytoplasm contains numerous structures called organelles (little organs) which carry out specific functions. Many organelles are bounded by membranes & form sub compartments within the cytoplasm.

- The cytoplasmic compartment contains the cytoskeleton which is a network of tubules & filaments, that give cells their three-dimensional shape & also binds to enzymes in their metabolic pathways, increasing cellular efficiency.

- It follows interphase & a rapid even by all cell standards, which lasts only about 1 hour in mammalian cells.

- It requires 2 separate but related processes: mitosis (nuclear division) & cytokinesis (cytoplasmic division).

The chromosome:

- Chromosomes contain the genetic information of cells; DNA which directs most cellular events.

- Chromosomes in most cells of the body exist in pairs & in humans for example there are 23 homologous chromosomes.

- The presence of homologous chromosome pairs results from sexual reproduction which is the uniting of a sperm & an ovum (germ cells).

- Each organism has set number chromosomes & in all the body, except germ cells, are called somatic cells & they contain a full complement of chromosomes.

- Germ cell or gametes contain half the number of chromosomes of somatic cells & are referred to as haploid cells.

- Gametes are produced by special type of cell division known as meiosis which occurs in the gonads (ovaries & testes).

- The chromosomes are loosely arranged in the nucleus during the interphase, but condense during the prophase.

- Condensation facilitates chromosome separation.

- Chromosome condensation allows morphological study of chromosomes & chromosomes arranged according to size form a karyotype, which allows geneticists to count chromosomes & to locate gross abnormalities.

- Although somatic cells contain a set number of chromosomes, the number of chromatids varies (chromosomes may contain one or two chromatids) depending on the stage of the cell cycle.

Cell Division:

- It has two major stages, mitosis & cytokinesis.

- During cellular division, the cell divides its chromosomes equally & distributes its cytoplasm & organelles move or less evenly between the two daughter cells.

- Cell division is essential for reproduction & growth. It is the basis of tissue repair & provides replacements for cells lost through normal wear & tear.

- The three major stages of cell division are:

(1) Mitosis (nuclear division):

- This stage is divided into four stages: Prophase, metaphase, anaphase (see table 15-1).

- Successful mitosis depends on the presence of the mitotic spindle (an array of microtubules that forms during prophase.

- Some of the spindle fibers attach to the chromosomes & help pull them apart during anaphase.

(2) Cytokinesis (the division of the cytoplasm);

- It begins late in anaphase or early telophase.

- In human cells, cytokinesis results from the contraction of microfilaments lying beneath the plasma membrane.

- This process results in two daughter cells with more or less equal amounts of cytoplasm.

- With this equal allocation of cytoplasm to the daughter cells comes a sharing of the cell's organelles.

Control of the cell cycle:

- The understanding of the control of the cell cycle is yet incomplete.

- Research suggests that the cell cycle is partly controlled by substances produced in the cytoplasm.

- These chemicals cause changes in the cell nucleus.

- -External controls such as hormones (e.g. the hormone estrogen from female ovaries) growth regulators; growth promoting & growth inhibiting factors & cell contact (contact inhibition in cell culture).

- Many other factors play a role depending on the type of cell. These factors may act directly on the cytoplasm but may likely induce genetic changes in the nucleus that regulate the cell cycle.

- Activation of these genes may lead to production of chemicals in the cytoplasm that diffuse back into the nucleus.

MEIOSIS & GAMETE FORMATION:

Meiosis:

- A type nuclear division that resembles mitosis & occurs in germ cells & yields haploid gametes (contains half the number of chromosomes) & requires two cellular divisions & in humans it reduces the chromosome number from 46 to 23.

- Germ cells are formed in reproductive organs; the ovaries & testes (the gonads). When germ cells unite they form a zygote (with 46 chromosomes) which continues to divide to form an embryo, a fetus, a baby & an adult.

- Though meiosis sexually reproducing organisms half the number of chromosomes in germ cells in the gonads of sexually reproducing animals.

- Meiosis involves two nuclear divisions or phases; meiosis I & II.

Meiosis I:

- It is often called a reduction division.

- During this first division the chromosome number is halved, thus a diploid cell produces 2 haploid cells.

Meiosis II:

- The second meiotic division is virtually identical to mitosis, except for the fact that the cells are haploid.

- When haploid cells divide in meiosis II, they produce two new cells, each containing a haploid number of single-stranded (unreplicated, or one chromatid) chromosomes.

- In males, meiosis produces four gametes (sperm cells) & in females, it produces only one egg.

PRINCIPLES OF HERIDITARY: MENDELIAN GENETICS

- Gregor Mendel, a nineteenth-century monk, discovered several several important principles of inheritance from his work on garden peas.

- Mendel determined that in peas, traits (characteristic e.g. color) do not blend (mix) as was commonly thought at the time.

- He also postulated that each adult has two hereditary factors (genes) for a given trait & that these factors separate during gamete formation & he called this notion the principle of segregation.

- Mendel also postulated that a hereditary factor might be either dominant or recessive.

- A dominant factor masks a recessive factor.

- A recessive factor is expressed only when the dominant factor is missing.

- The dominant & recessive genes are alternative forms of the genes or alleles.

- The genetic make up of an organism is called its genotype

- The physical appearance which is determined by the genotype & its environment is the phenotype.

- From his studies, Mendel concluded that the hereditary were separated independently of one another during gamete formation & this is known as the principle of independent assortment & holds true only for non-linked genes.

MENDELIAN GENETICS IN HUMANS:

- Human cells contain 23 pairs of chromosomes; 22 pairs of autosomes & one pair of sex chromosomes.

- Chromosomes carry dominant & recessive traits & inheritance of these traits is consistent with Mendel's principles of inheritance, although additional mechanisms are at work in humans & other organisms.

- Sickle-cell anemia, cystic fibrosis, & albinism are autosomal-recessive traits & are expressed individuals.

- Widow's peak, achondroplasia (dwarfism resulting in short bones), & Marfan's syndrome (affects the skeletal system, the eye & the cardiovascular system) are autosomal dominant traits & are expressed in heterozygous & homozygous dominant genotypes.

Mendel's Laws of Genetics:

These laws are considered the corner stones of modern genetics. They were first postulated by Gregor Mendel in 1865.

Law 1: Unit Inheritance: the characteristics of parents do not mix in the offspring. The characteristics of parents, though they might not be expressed in the first generation, they could reappear quite unchanged in a later generation.

Law 2: Segregation: The two members of a single pair of genes are never found in the same gamete but instead always segregate. In exceptional circumstances when the members of a chromosome pair fail to segregate, this rule is broken & the result is severe abnormality.

Law3: Independent assortment: Members of different gene pairs assort to the gametes independently of one another. In other words, there is a random recombination of the prenatal & maternal chromosomes in the gametes.

- The development of Genetics as a science dates not from Mendel's paper but from the papers that reported the rediscovery of his laws.

The genetic Code:

- The genetic information is stored in DNA by means of a code in which 3 adjacent bases constitute a codon, coding for a specific amino acid. Since there are four nucleotide bases: adenine, guanine, cytosine & thymine, and each amino acid is coded for by three bases, the number of possible combinations is 43 which is 64. This means that every one of the 20 amino acid is coded for by more than one codon. Three of these 64 codons are 'nonsense' codons designating termination of a message.

- The genetic information is contained in the DNA in the nucleus of the cell, but translation (i.e. polypeptide synthesis) takes place in the cytoplasm in association with the ribosomes. The link between the DNA & polypeptide is the RNA.

Dr. Yasser babair