The Cell: Structure, Function, and Cell Cycle

THE CELL DENNIS KIDIYA BSC. CLIN. MED CELL STRUCTURE STRUCTURE AND FUNCTION 1.Cell Membrane A thin semi permeable membrane layer of protein and fats surrounding the cell. ROLES; a) Protection. b) Selective permeability/Transport c) Communication d) Cellular recognition STRUCTURE OF CELL M...

THE CELL DENNIS KIDIYA BSC. CLIN. MED CELL STRUCTURE STRUCTURE AND FUNCTION 1.Cell Membrane A thin semi permeable membrane layer of protein and fats surrounding the cell. ROLES; a) Protection. b) Selective permeability/Transport c) Communication d) Cellular recognition STRUCTURE OF CELL MEMBRANE 2. Cytoplasm a jelly-like material which contains all the cell organelles, enclosed within the cell membrane. Roles; 1. Site for biochemical reactions eg glycolysis 2. Contains cellular organelles and the cytoskeleton 3. Intracellular transport 4. Storage site eg for proteins, lipids, ions 5. Essential in cell division 3. Mitochondrion Are spherical or rod-shaped organelles with a double membrane. They are the powerhouse of a cell as they play an important role in energy production. It is along this inner membrane that a series of proteins, enzymes, and other molecules perform the biochemical reactions of cellular respiration. reactions convert energy stored in nutrient molecules (such as glucose) into adenosine triphosphate (ATP), Oxygen molecules are required but not always necessary during cellular respiration Krebs cycle (also known as the citric acid cycle), fatty acid oxidation, and the electron transport chain (ETC) leading to oxidative phosphorylation (OXPHOS)- are the processes that lead to energy production in the mitochondria 4. Nucleus The nucleus is the largest and most prominent of a cell’s organelles Considered the control center of the cell because it stores all of the genetic instructions for manufacturing proteins Some cells can be multinucleated eg muscle cells, some cane be anucleated the nucleus is surrounded by a membrane called the nuclear envelope Inside the nuclear envelope is a gel-like nucleoplasm with solutes that include the building blocks of nucleic acids The nucleolus is a region of the nucleus that is responsible for manufacturing the RNA necessary for construction of Cont. The genetic instructions that are used to build and maintain an organism are arranged in an orderly manner in strands of DNA. Which form threads called chromatin 5. Endoplasmic Reticulum(ER) a system of channels that is continuous with the nuclear membrane Has 2 types a) Smooth ER- synthesis of lipids. The smooth ER synthesizes phospholipids, the main component of biological membranes, as well as steroid hormones. -also sequesters and regulates the concentration of cellular Ca++ b) Rough ER- CONTAINS RIBOSOMES which serves as the site of protein synthesis from mRNA 6. Golgi Apparatus is responsible for sorting, modifying, and shipping off the products that come from the rough ER looks like stacked flattened discs has two distinct sides One side of the apparatus receives products in vesicles. These products are sorted through the apparatus, and then they are released from the opposite side after being repackaged into new vesicles. 7. Lysosomes is an organelle that contains enzymes that break down and digest unneeded cellular components, such as a damaged organelle are also important for breaking down foreign material. For example, when certain immune defense cells Play a major role in apoptosis(programmed cell death), ‘self destruct button’ 8. Peroxisomes Play a role in lipid metabolism and detoxification- clearance of reactive oxygen species through action of enzymes it stores 9. The Cytoskeleton helps the cells to maintain their structural integrity. are also critical for cell motility, cell reproduction, and transportation of substances within the cell. Made up of 3 different types of fibres ; a) Microfilaments- thinnest and important in muscle contraction b) intermediate filaments- maintain cell structure resist pull forces c) Microtubules-thickest maintain cell shape and structure, help resist compression of the cell, and play a role in positioning the organelles within the cell., make up cilia and flagella set the paths along which the genetic material can be pulled during cell division THE CELL CYCLE Ordered series of events involving cell growth and cell division that produces 2 new daughter cells. Has 4 basic steps to it.  DNA(Deoxyribonucleic Acide) REPLICATION cells must replicated themselves by dividing to produce 2 new daughter cells, each with the full complement of DNA as found in the original cell. A DNA molecule is made of two strands that “complement” each other: the molecules that compose the strands fit together and bind to each other, creating a double-stranded molecule that looks much like a long, twisted ladder.(Double Helix) Made up of; a) 5 carbon sugar b) Nitrogenous base-Adenine, Cytosine, Thymine/Uracil,Guanine c) Phosphate group  DNA replication is the copying of DNA that occurs before cell division can take place. Has 3 stages; a) INITIATION-The two complementary strands are separated, much like unzipping a zipper. Special enzymes, including helicase, untwist and separate the two strands of DNA. b) ELONGATION-Each strand becomes a template along which a new complementary strand is built. DNA polymerase brings in the correct bases to complement the template strand, synthesizing a new strand base by base. c) TERMINATION-Once the two original strands are bound to their own, finished, complementary strands, DNA replication is stopped and the two new identical DNA  Mistakes made during DNA replication(MUTATIONS), such as the accidental addition of an inappropriate nucleotide, have the potential to render a gene dysfunctional or useless. A DNA proofreading process enlists the help of special enzymes that scan the newly synthesized molecule for mistakes and corrects them. Only after correction that division can progress if not the cell can undergo apoptosis or go into G0 RIBONUCLEIC ACID( RNA) Types of RNA Messenger RNA (mRNA) Function: Carries genetic information from DNA to ribosomes for protein synthesis. Template for translation Ribosomal RNA (rRNA) Function: A structural component of ribosomes that helps in protein synthesis. It facilitates the binding of mRNA and tRNA during translation. Transfer RNA (tRNA) Function: Delivers specific amino acids to ribosomes during protein synthesis. Process of Cycle 1. G1(GAP PHASE 1) A cell grows and carries out all normal metabolic functions and processes. The cell is accumulating the building blocks of chromosomal DNA and the associated proteins as well as accumulating sufficient energy reserves to complete the task of replicating each chromosome in the nucleus. from a microscopic aspect, little change is visible. 2. S –PHASE( SYNTHESIS PHASE) is period during which a cell replicates its DNA. result in the formation of identical pairs of DNA molecules—sister chromatids—that are firmly attached to the centromeric region. The centrosome is duplicated during the S phase. The two centrosomes will give rise to the mitotic spindle, the apparatus that orchestrates the movement of chromosomes during mitosis. 3. G2 (GAP PHASE 2) the cell continues to grow and makes the necessary preparations for mitosis. Some cell organelles are duplicated, and the cytoskeleton is dismantled to provide resources for the mitotic phase. 4. MITOTIC PHASE is a multistep processes during which the duplicated chromosomes are aligned, separated, and move into two new, identical daughter cells. Has 6 steps to it MITOTIC PHASE 1. PROPHASE is the first phase of mitosis, during which the loosely packed chromatin coils and condenses into visible chromosomes. The nucleolus disappears early during this phase, and the nuclear envelope also disintegrates. The centrosomes begin to move to opposite poles of the cell. microtubules begin to extend from each like long fingers from two hands extending toward each other. The sister chromatids begin to coil more tightly with the aid of condensin proteins and become visible under a light microscope. 2. PROMETAPHASE Chromosomes continue to condense Kinetochores appear at the centromeres Mitotic spindle microtubules attach to kinetochores 3. METAPHASE Chromosomes are lined up at the metaphase plate Each sister chromatid is attached to a spindle fiber originating from opposite poles 4. ANAPHASE Centromeres split in two Sister chromatids (now called chromosomes) are pulled toward opposite poles Certain spindle fibers begin to elongate the cell 5.TELOPHASE Chromosomes arrive at opposite poles and begin to decondense Nuclear envelope surrounds each set of chromosomes The mitotic spindle breaks down Spindle fibers continue to push poles apart 6. CYTOKINESIS a cleavage furrow separates the daughter cells