Cells and Cell Cycle PDF

CELLS AND ITS COMPONENTS Somatic Cells (body cells) – have two copies of the genome and are said to be diploid Germ Cells – a sperm and egg cells and have one copy of the genome and are haploid Stem Cells - diploid cells that divide to give rise to di erentiated cells and to oth...

CELLS AND ITS COMPONENTS Somatic Cells (body cells) – have two copies of the genome and are said to be diploid Germ Cells – a sperm and egg cells and have one copy of the genome and are haploid Stem Cells - diploid cells that divide to give rise to di erentiated cells and to other stem cells in a process called self-renewal PRIMARY TYPES OF TISSUE  Epithelial Tissues  Connective Tissues  Muscular tissues  Nervous Tissues CLASSIFIED ACCORDING TO CELL SHAPE CLASSIFIED ACCORDING TO NO. OF LAYERS Squamous Simple Cuboidal Pseudostratified Columnar Stratified Transitional CELLS Prokaryotic cell – does not have a nucleus, the Eukaryotic cell – distinguished from a structure that contains DNA in the cells of other prokaryotic cell by structures called organelles, types of organism. which perform specific functions. - single membrane - bilayer membrane - no well-defined nucleus - nucleus containing DNA and histones - no membrane bounded organelles - membrane bounded - lysosome is absent - lysosome present - RNA and protein synthesis in same - RNA in nucleus and proteins in the cytosol compartment CHEMICAL CONSTITUENTS  Carbohydrates – provide energy and contribute to cell structure  Lipids – from the basis of some hormones, form membrane, provide insulation, and store energy  Proteins – enable blood to clot, form the contractile fibers of muscle cells, and form the bulk of the body’s connective tissues  Nucleic acids – involves the storage and expression of genomic information  NUCLEUS  directs cells activities  known as the control center of the cell  separated from cytoplasm by nuclear membrane  this contains the genetic material – DNA  replication and transcription ABOUT THE DNA DNA resembles a spiral staircase or double helix. The “rails” or backbone, consists of alternating chemical groups (sugar and phosphates) and are the same in al DNA molecules The “steps” of the DNA double helix are pairs of the four types of building blocks, or nitrogen bases: Adenine (A) and Thymine (T), which attract each other and Cytosine (C) and Guanine (G)  DNA can both perpetuate itself when a cell divides and provide information to manufacture specific proteins   Accessing genetic information occurs in three processes:  Replication of DNA: the DNA untwists, separates, and builds a new partner chain; DNA is copied to produce a second, identical DNA  Transcription of RNA: a temporary copy of information in RNA is made using DNA as a template; copies the sequence of part of one strand of a DNA molecule into a related molecule, messenger ribonucleic acid (RNA)  Translation of protein form RNA: the base sequence pf mRNA is decoded to make a sequence of amino acids MUTATION  a change in a gene, or mutation, can have an e ect at the whole-person level, such as causing a disease  once a gene mutates, the change is passed on when the cell that contains it divides CHROMOSOMES  a human somatic cell (non-sex cell) has 23 pairs of chromosomes  twenty two of these 23 pairs are autosomes, which do nit di er between the sexes  the other two chromosomes, the X and the Y, are sex chromosomes GENOTYPE PHENOTYPE - genetic composition of an organism - the visible trait, biochemical change, or - refers to the pair of alleles e ect on health - refers to the underlying instructions - refers to the expression of the trait - the visible expression of information contained in a gene ALLELES - cells normally have two copies (alleles) of autosomal genes on chromosomes other than the X and Y. One allele is inherited form the mother (maternal allele) and one is inherited from the father (paternal allele NUCLEOLUS  found inside the nucleus  it contains the RNA to build the proteins  major site where ribosome subunits are being assembled NUCLEAR MEMBRANE  surrounds nucleus  bilayer membrane  openings of the nuclear membrane allow material to enter and leave nucleus GLYCOCALYX  a dense, gel-like meshwork that surrounds the cell, constituting a physical barrier for any object to enter the cell  prevent the entry of pathogens onto the cell  made up of glycoproteins and glycolipids MITOCHONDRIA  powerhouse of the cell; generates energy ATP from TCA  bounded by two concentric membranes that have di erent properties and biological functions  Outer Membrane: lipid bilayer and proteins  Inner Membrane: protein the lipids ENDOPLASMIC RETICULUM  membrane complexes that are interconnected by separate organelles  varies in shape, size, and amount, the ER extends from the cell membrane, coats the nucleus, surrounds the mitochondria  Rough ER  Smooth ER - contains ribosomes - no ribosomes - synthesizes membrane lipids, and - lipid synthesis and modification and secretory proteins; these are then inserted transport of proteins synthesized in the rough through the ER membrane and transported ER through the cell GOLGI APPARATUS  site where sugars are made and linked into starches or joined to lipids or proteins; proteins finish folding; secretions stored  Cis side (proximal): receives the newly synthesized proteins by the ER via transfer vesicles  Trans side (distal): release proteins via modified membranes called secretory vesicles; excreted by exocytosis RIBOSOMES  a cell needs a ribosome to be able to form and synthesize proteins that are needed by the cell  protein is significantly important in providing the structural support and in controlling most of the chemical reactions in the cell  synthesis happens in the cytoplasm, nucleolus, and nucleoplasm LYSOSOMES  degrades debris; recycles cell contents  contains proteolytic enzymes or digestive enzymes  enzymes act locally but when the lysosomal membrane ruptures the autolysis occurs and cell death is imminent PEROXISOMES  breaks down and detoxifies various molecules  also called micro bodies  they carry out oxidation reaction in which toxic H2O2 is produced, which is destroyed by the enzyme catalase CYTOSKELETON  supports cell organelles and nucleus while maintaining cell integrity  a meshwork of protein rods and tubules that serves as the cell’s architecture, positioning organelles and providing overall three-dimensional shapes  Microtubules: made up of tubulin protein forms spindles during cell division; maintain cellular organization and enable transport of substances within the cell  Microfilament: produces force inside the cell  Micro trabeculae CELLS DIVISION AND DEATH THE CELL CYCLE  describe the sequence of activities as a cell prepares for and undergoes division  varies in di erent tissue at di erent times  it is continual, but we describe it with stages  interphase and mitosis INTERPHASE  a cell continues the basic biochemical functions of life, while also replicating its DNA and some organelles  divided into two gaps: G1 and G2 and one synthesis phase (S phase)  In addition, a cell can exit the cell cycle at G1 to enter a quiet phase called G0 G1 PHASE  the cell resumes synthesis of proteins, lipids, and carbohydrates  G1 is the period of the cell cycle that varies the most in duration among di erent cell types  Duration usually varies but most likely to finish within 10-11 hours S PHASE  The cell replicates its entire genome; the cell synthesizes complete copy of the DNA and its nucleus  After DNA replication, each chromosome consists of two copies of the genome joined at an area called the centromere  8-10 hours G2 PHASE MITOSIS  occurs after the DNA has been  the replicated chromosomes are replicated but before mitosis begins condensed enough to be visible  more proteins are synthesized during  long strands of chromosomal material this phase are called chromatids  lasts for 4 hours  has four phases: Prophase, Metaphase, Anaphase, and Telophase PROPHASE ANAPHASE - DNA coils tightly - a bond of microfilaments forms on the inside - This coiling shortens and thickens the face of the plasma membrane chromosomes, easing their separation - the centromeres’ part, which relieves the - Toward the end of prophase, the nuclear tension and releases one chromatid from each membrane breaks down. The nucleolus is no pair to move to opposite ends of the cell longer visible - the sister chromatids separate from each other and are pulled towards opposite ends of the cell METAPHASE - chromosomes attach to the spindle at their TELOPHASE centromeres and align along the center of the - the final stage of mitosis, the cell looks like a cell, which is called the equator dumbbell with a set of chromosomes at each - nucleus dissolves and the cell’s chromosomes end. The spindle falls apart, and nucleoli and the condense and move together, aligning in the membranes around the nuclei re-form at each center of the dividing cell end of the elongated cell How can a cell know how many divisions remain? - the answers lie in the chromosome tips, called telomeres. Telomeres functions like cellular fuses that burn down as pieces are lost from the ends - at each mitosis, the telomeres lose 50 to 200 endmost bases, gradually shortening the chromosome APOPTOSIS  rapidly and neatly dismantles a cell into membrane-enclosed pieces that a phagocyte can mop up  within seconds, enzymes called caspases are activated inside the doomed cell, stimulating each other and sniping apart various cell components These killer enzymes: - destroy enzymes that replicate and repair DNA - activate enzymes that cut DNA into similarly sized pieces - tear apart the cytoskeletons, collapsing the nucleus and condensing DNA within - causes mitochondria to release molecules that increase caspase activity and end the energy supply - abolish the cell’s ability to adhere to other cells - attract phagocytes that dismantle the remnants APOPTOSIS NECROSIS - programmed cell death - pathologic cell death - controlled death of individual cells - a ects group of cells - induced by physiological stimuli - triggered by non-physiological events - no inflammation - presence of inflammation - shrinking of cytoplasm and condensation - swelling of the cytoplasm and of nucleus mitochondria - intact cellular contents, may be released - cellular contents may leak out of the cell in apoptotic bodies