Cell Biology (2023) PDF

Cell biology Dr Kholood Baron Cells are Us A person contains about 100 trillion cells. That’s 100,000,000,000,000 or 1 x 1014 cells. There are about 200 different cell types in mammals (one of us). Cells are tiny, measuring on average about 0.002 cm (20 um) across. That’s about 1250 cells, “shoul...

Cell biology Dr Kholood Baron Cells are Us A person contains about 100 trillion cells. That’s 100,000,000,000,000 or 1 x 1014 cells. There are about 200 different cell types in mammals (one of us). Cells are tiny, measuring on average about 0.002 cm (20 um) across. That’s about 1250 cells, “shoulder-to-shoulder” per inch. Cell chemical composition Cells are made of protoplasm, the building material for all living things, it’s responsible for: - Complex process of metabolism - Reception and processing of food and oxygen - Elimination of waste product. protoplasm, consists of: - Organic compounds (contain carbon, hydrogen, and oxygen) - Inorganic materials (do not contain carbon) • Biomolecular that compromise protoplasm are formed from 24 elements, the 4 primary elements: • Carbon • Hydrogen • Oxygen • Nitrogen • When combined with phosphorus and sulfur they comprise the essential major organic compounds: • Proteins • Carbohydrates • Lipid nucleic acid Cells compounds: • Inorganic compounds (water and mineral salts (electrolytes). • Organic compounds (proteins, carbohydrates, nucleic acids, lipids) Most important Inorganic compound is Water (many role in the body) • A medium in which acids, bases and salts are dissolved • Function as a solvent by dissolving chemical substances in the cell • Function as a transport vehicle for materials the cell uses or eliminates. • Maintain a constant body cor temperature • Provide a cushion for vital organs • Regulates concentration dissolved substances • Lubricates the digestive system and joints and lining of the organs. Organic compounds that compose the cell 1. 2. 3. 4. Protein Carbohydrates (simply sugar) Lipids ( simply fat) Nucleic acid 1- protein • Contain the most carbon • Most important elementary building block if the cell (15% of cell content). • Protein is a combination of amino acids NH2 (amin) COOH (carboxylic acid). • Amino acid are natural monomer, when they link by peptide bonds they form polymer. • Chromosome and genes organize the amino acids into different orderings to make different types of protein. Types of protein • Structural protein. Provide the body with its shape and form and are source of heat and energy ( found in muscles) • Enzymatic protein: function as organic catalysts, ( affect the rate or speed of chemical reactions without being altered themselves, called enzymes. • Repair enzymes : these proteins mend the damaged molecules so they help the cell to recover from a small amount of radiation induced damage. Thier catalytic and repair capabilities are important for the cell survival. ( but this ability and efficiency to rapier have limitation!!) - protein may function as hormones and antibodies 2- Carbohydtaes, saccharides or simply Sugars carbohydrates are chain of sugar molecules, - Their primer function is > short –term energy - Simplest monoccharide ( glucose , fructose and galactose, No needed to know We just need to think about it 3- Fatty Acids (Lipid) A 4- Nucleic acids • Large complex macromolecules, made from nucleotides, • 2 types of nucleic acid that are important for human metabolism: • DNA • RNA 4 Nitrogen organic bases in DNA adenine ( A) Cytosine ( C), Guanine ( G) Thymine ( T) The DNA molecules are extremely long and hence without the right packaging, they cannot fit into cells. Thus, DNA is tightly coiled to produce chromosomes. Every chromosome has a single DNA molecule. WE have 23 pairs of chromosomes within the nucleus of the cells. Human genoma • Genetic information contained in nucleic acids is stored and replicated in chromosomes, • A chromosome is a deoxyribonucleic acid (DNA) molecule, and genes are segments of intact DNA .. Called genoma • The process of locating and identifying the gens in the genoma is called mapping Ribonucleic Acid (RNA) Its main role is to act as a messenger conveying instructions from DNA for controlling the proteins synthesis. Types Of RNA • mRNA – The messenger RNA encodes amino acid sequences of a polypeptide • tRNA– The transfer RNA carries amino acids to ribosomes while translation • rRNA – The ribosomal RNA produces ribosomes with the ribosomal proteins that are organelles responsible for the translation of the mRNA. The difference between DNA and RNA • RNA is a single strand structure, DNA is a double stand structure • RNA contains ribose, DNA contains Deoxyribose • RNA have uracile with adenine in its base, DNA has thymine paired with adenine in its base • RNA perform many different biological functions; DNA carries the genetic information. • RNA is much shorter compared to the long DNA chain The Flow of information from DNA to create a protein • DNA transmit its information outside of the cell by reproducing messenger RNA (mRNA- resemble one-half of the DNA), that leave the cell to create the protein with the help of transfer RNA (tRNS) • The flow of information from nucleic acids to protein is: DNA —> messenger RNA (mRNA) —> transfer RNA (tRNA) —> ribosomal RNA (rRNA) —> protein. • This indicates that the nucleotide sequence in a gene of DNA specifies the assembly of a nucleotide sequence in an mRNA, which in turn directs the assembly of the amino acid sequence in protein through a tRNA and rRNA molecules Cellular Structure 1- Cell membrane 2- Nucleus 3- Cytoplasm 4- Cytoplasmic organells 1- Cell membrane • Made up of lipid and proteins • Function as a barricade to protect cellular content from the outside environment • Control the passage of water and other materials into and out of the cell 2- The Nucleus - Nucleus is surrounded by the nuclear envelope - a double membrane - Nuclear membrane has nuclear pores that control entry and exit of materials Think of the nucleus as the cell’s control center. Chromosome - “colored body” - seen as chromosomes and protein when highly condensed in preparation for cell division. At other times the DNA and protein are threadlike - The most common proteins are histones. - DNA is coiled around histones in a regular pattern that produces structures called histones. 3- Cytoplasm • Is the Protoplasm that exists outside the nucleolus. Function: • Accepts and builds up unrefined materials to form new substances such as lipid and protein. • Breaks down organic materials to produce energy (catabolism) • Package substances for distribution to other area of the cell or all the body through the circulation • Eliminates waste products. 4- Cytoplasmic Organelles • Contains all the miniature cellular components that enable the cell to function in a highly organized manner. A- Endoplasmic reticulum B- Golgi apparatus or complex C- Mitochondria D- Lysosomes E- Ribosomes F- Centrosomes • DNA determines the function of each of them A- Endoplasmic reticulum web-like series of membranes within the cytoplasm in the form of flattened sheets, sacs, tubes, creates many membrane enclosed spaces throughout the cytoplasm - has connections with the outer membrane of the nucleus and the plasma membrane Function: - Circulation and transport - Storage of proteins and minerals - Synthesis of lipids, carbohydrates, and proteins -A large surface area for enzyme action Two types of ER - rough and smooth - Rough ER - involved in protein synthesis with ribosomes site of synthesis of many proteins – - Smooth ER - site for synthesis of steroids and other lipids Ca++ storage in muscles detoxification of drugs, toxins, alcohol (especially in liver) The highly convoluted surface provides a large surface area for enzymatic activities. Many enzymes are imbedded in the membranes. The Rough Endoplasmic Reticulum Functions: -Protein synthesis (about half the cell’s proteins are made here). -Protein movement (trafficking) -Protein “proofreading” B- Golgi apparatus or complex The Golgi is functionally associated with the ER. Proteins synthesized on the ER are concentrated internally and transport vesicles are budded off Transport vesicles fuse with the Golgi, dump their contents into the Golgi Golgi packages proteins in vesicles so that they may be excreted from Secretory vesicles - used for excretion the cell, or used within leave the Golgi and move to plasma the cell. membrane where they fuse and dump their contents outside - seen in many The Golgi Apparatus also forms lysosomes Lysosomes - vesicles filled with digestive enzymes - used for intracellular digestion Particles can be taken into cell by phagocytosis and vesicle fused with lysosome The components of organelles can be recycled after digestion by lysosomes C- Mitochondria Mitochondria - cellular powerhouses - the site of much of the energy harvest by cells have double membrane structure inner membrane folded into inward projections called cristae two spaces within the mitochondrion the matrix and the intermembrane space Mitochondria  The site of oxygen consumption within cells  Have their own DNA.  Have their own ribosomes that are similar in construction to prokaryotic ribosomes  Synthesize many, not all, of their own proteins D- Lysosomes Functions: • Digesting food or cellular invaders • Recycling cellular components • Cell suicide (suicide is bad for cells, but good for us!) E- Ribosomes Ribosomes - protein synthetic machinery • two subunits - large and small - each made of protein and ribosomal RNA (rRNA) • subunits associate when they are synthesizing proteins • protein synthesis occurs on ribosomes that are free-floating in the cytoplasm and on ribosomes attached to ER • rRNA is synthesized in the nucleolus F- Centrosomes • Located near the nucleolus • Contain centriols from which the spindle fibers develop in cell division. Functions: •Help in cell division. •Maintain the chromosome number during cell division. •Stimulate the changes in the shape of the cell membrane by phagocytosis. •In mitosis, it helps in organizing the microtubules ensuring that the centrosomes are distributed to each daughter cell. Centrioles - are part of specialized region of the cell called the centrosome (cell center) found in animals and most protists the centrioles are involved in the production of microtubules microtubules have many functions including moving chromosomes during cell division centriole structure - 9 triplets of microtubules surrounding a hollow core similar to the basal body of flagella Cell Division Mitosis & Meiosis - Human cells are either germ (sexual) cells (ie. sperm or egg) or somatic cells (other human cells) Cells propagate through division: • Division of somatic cells is called mitosis and results in two genetically identical daughter cells. • Division of germ cells is called meiosis and involves two fissions of the nucleus giving rise to four sex cells, each possessing half the number of chromosomes of the original germ cell. Mitosis Division of somatic cells. A single cell divides into two identical daughter cells. The New cells themselves may undergo further division, and the process continues producing a large number of progeny. Daughter cells have same number of chromosomes as does parent cell. ( identical chromosome to the original cell). Packing for the move… When the cell is not dividing… • DNA molecules are in extended, uncondensed form = chromatin • Cell can only replicate and transcribe DNA when it is in the extended state. When the cell is preparing for division… • DNA molecules condense to form chromosomes prior to division. • easier to sort and organize the replicated DNA into daughter cells Mitosis 4 sub-phases: 1st – Prophase 2nd – Metaphase 3rd – Anaphase 4th – Telophase followed by Cytokinesis 1. Prophase chromatin nucleus condensing chromosomes nucleolus centrioles Three Major Events 1. chromosomes condense 2. spindle fibers form (spindle fibers are specialized microtubules radiating out from centrioles) 3. chromosomes are captured by spindle 2. Metaphase • chromosomes align along the equator of the cell, with one chromatid facing each pole centrioles chromosomes spindle fibers 3. Anaphase • Sister chromatids separate • Spindle fibers attached becomes shorten and pull chromatids towards the poles. • Free spindle fibers lengthen and push the poles of the cell apart 4. Telophase • Spindle fibers disintegrate • Nuclear envelopes form around both groups of chromosomes • Chromosomes revert to their extended state • Cytokinesis occurs, enclosing each daughter nucleus into a separate cell Germ or sexual cell division Meiosis - Single germ cell divides into four unique daughter cells. - Daughter cells have half the # of chromosomes as parent cell, so they are considered haploid. Genetics Terminology: Ploidy Needed to be known Refers to the number of sets of chromosomes in cells. ● Haploid – one copy of each chromosome – designated as “n”, the number of chromosomes in one “set” – gametes ● Diploid – two sets of chromosomes (two of each chromosome) – designated as “2n” – somatic cells Diploid organisms receive one of each type of chromosome from female parent (maternal chromosomes) and one of each type of chromosome from male parent (paternal chromosomes) Sexual reproduction in humans … • At fertilization, 23 chromosomes are donated by each parent. (total = 46 or 23 pairs). • Gametes (sperm/ova): – Contain 22 autosomes and 1 sex chromosome. – Are haploid (haploid number “n” = 23 in humans). • Fertilization results in diploid zygote. – Diploid cell; 2n = 46. (n = 23 in humans) Meiosis - Sex Cell (Gamete) Formation In meiosis, there are 2 divisions of the nucleus: meiosis I & meiosis II Spermatogonium In Male Meiosis & Sexual Reproduction Life Cycle Mitosis * * * The result of meiosis • Production of four daughter cells. • These cells have one half the number of chromosomes as the original cell. • Only sex cells are produced by meiosis. Other cells are produced by mitosis. • When sex cells unite during fertilization, these haploid cells become a diploid cell. Diploid cells have the full complement of chromosomes. Genetic Variation in Diploid Organisms Fusion of sperm and egg results in unique offspring……because the young are a product of two individuals with different genetic makeup. Meiosis also “shuffles” the genes so that individual’s gametes are genetically different from one another. How are twins formed? Mitosis • 2 n (Diploid) • Clone • Same genetic information in parent cell and daughter cell. • Give me another one just like the other one! vs. Meiosis • 1 n (Haploid) • Daughter cells different from parent cell and from each other. • 4 Daughter cells have ½ the number of chromosomes as somatic cell. • Shuffling the genes