Cell Structures and Organelles

• Typical cells, also known as composite cells, vary in size, structure, and function, and are the fundamental unit of life.

Cell Structures

• Plasma membrane separates the cell from its surroundings, and is found in every cell except blood cells.
• Nucleus is a large membranous structure near the center of the cell, composed chiefly of rRNA (ribosomal RNA) and DNA, and made of the same material as the plasma membrane.
• Cytoplasm is a gel-like substance inside the cell, composed of numerous organelles suspended in a watery cytosol, and is essential for life.

Organelles

• Smooth ER synthesizes carbohydrates and lipids.
• Flagellum is only found in human male sperm.
• Nucleus contains DNA, the blueprint that makes individuals unique.
• Nuclear envelope surrounds the cell.
• Mitochondria are responsible for ATP production.
• Cilium are hairlike projections that help with absorption and move particles along.
• Microvilli are similar to cilium except to allow greater absorption.
• Lysosomes are the cell's own digestive system.
• Peroxisomes are responsible for getting rid of toxins.
• Ribosomes are attached to the rough ER, but some are 'free ribosomes' and stay within the cell for the cell's own use.

Cell Membranes

• Each cell contains a variety of membranes, including the plasma membrane, which protects the cell and controls what gets in and out, as well as membranous organelles.
• Membranous organelles include mitochondria, nucleus, endoplasmic reticulum, Golgi apparatus, lysosomes, peroxisomes, and vesicles.
• Non-membranous organelles include cytoskeleton, microvilli, centrioles, cilia, flagella, and ribosomes.
• Fluid mosaic model illustrates that the molecules of the cell membrane form a continuous sheet and molecules move around like a fluid.
• Integral membrane proteins (IMPs) control what moves through the membrane.
• Some IMPs have carbohydrates attached to them and form glycoprotein.
• Some IMPs are receptors that react to specific chemicals.

Cytoplasm and Organelles

• Cytoplasm is a gel-like internal substance of cells that includes many organelles suspended in a watery intracellular fluid called cytosol.
• Membranous organelles are sacs or canals made of cell membranes.
• Non-membranous organelles are made of microscopic filaments or other non-membranous materials.

Endoplasmic Reticulum

• Rough ER synthesizes proteins, which move toward the Golgi apparatus and eventually leave the cell.
• Rough ER is made up of membranous-walled canals and flat, curving sacs arranged in parallel rows throughout the cytoplasm, extending from the plasma membrane to the nucleus.
• Function of the rough ER includes protein synthesis and intracellular transportation.
• Smooth ER removes and stores calcium ions (Ca++) from the cell's interior.
• Smooth ER synthesizes certain lipids and carbohydrates and creates membranes for use throughout the cell.

Ribosomes

• Ribosomes synthesize protein.

Golgi Apparatus

• Golgi apparatus processes protein molecules from the endoplasmic reticulum.
• Processed proteins leave the final cisterna in a vesicle.
• After vesicles break away from the ER, they move to the golgi apparatus and fuse with the first cisterna.
• Once all processed proteins leave the final cisterna, the contents can then be secreted to outside the cell.

Lysosomes

• Lysosomes are microscopic membranous sacs that have “pinched off” from the Golgi apparatus.
• The interior of the lysosome contains various kinds of enzymes capable of breaking down all the protein components of a cell.
• Enzymes in lysosomes digest the protein structures of defective cell parts, including IMPs and particles that have become trapped in the cell.
• The size and shape of lysosomes change with the stage of their activity.
• Residual bodies contain indigestible materials.
• Residual bodies are either secreted by the cell via exocytosis, or they become lipofuscin granules that remain in the cytosol indefinitely.

Proteasomes

• Proteasomes are hollow, protein cylinders found throughout the cytoplasm.
• They break down protein molecules one at a time by tagging each one with a chain of ubiquitin molecules.
• Proteasomes break down abnormal/misfolded proteins and normal proteins no longer needed by the cell.
• Ubiquitin enters the proteasome and pulls the rest of the protein in after it; the protein is unfolded, and the peptide bonds begin to break apart.

Peroxisomes

• Peroxisomes are small membranous sacs containing enzymes that detoxify harmful substances that enter the cells.
• Peroxisomes are often seen in kidney and liver cells.
• They contain the enzymes peroxidase and catalase, which are important in detoxification.

Mitochondria

• Mitochondria are made up of microscopic sacs.
• Double membrane structure that is contorted into folds called cristae.
• The "power plant” of cells that produce ATP.
• Each mitochondrion has a DNA molecule.

Structure of the Nucleus

• Consists of a nuclear envelope (composed of two membranes, each with essentially he same molecular structure as the plasma membrane) surrounding nucleoplasm.
• Contains DNA, the hereditary molecules, and appears as Chromatin threads or granules in non-dividing cells or Chromosomes in early stages of cell division.

Cytoskeleton

• Every cell in the body has a cytoskeleton.
• It is the cell's internal supporting framework which is made up of tiny, flexible fibers and rigid, rodlike pieces.
• It can move the cell or its parts and detects changes inside and outside the cell.

Cell Fibers

• Fibers appear to support the ER, mitochondria and “free” ribosomes.
• Microfilaments serve as a cellular muscle, sliding past each other to cause shortening of the cell.
• Microtubules are tiny, hollow tubes; they are the thickest of the cell fibers.

Centrosome

• Centrosome is a non-membranous structure also called the microtubule organizing center (MTOC).
• The centrosome plays an important role during cell division.
• The general location of the centrosome is identified by the centrioles.
• It is an area of the cytoplasm near the nucleus that coordinates the building and breaking apart of the microtubules in the cell.

Cell Extensions

• Microvilli assists epithelial cells in absorption.
• Cilia are shorter and more numerous than flagella with sensory functions.
• Flagella are found on on human sperm cells.

Connections Between Cells

• Tight junctions occur in cells that are joined by “collars” of tightly fused material and allow nothing to get through (lots in the small intestine).
• Molecules cannot permeate the cracks of tight junctions.

Cell Growth and Reproduction

• Cell growth and reproduction are the most fundamental of all living functions and constitute the cell life cycle.
• Cell growth depends on the use of genetic information in DNA to make the structural and functional proteins needed for cell survival.
• Cell reproduction ensures that genetic information is passed from one generation to the next.

Protein Synthesis

• Protein synthesis is a central anabolic pathway in cells where deoxyribonucleic acid (DNA) functions to transfer information, encoded in genes, to direct the synthesis of proteins.
• Protein synthesis is also important process because it influences all cell structures and functions.
• As it is formed, the mRNA molecule separates from the DNA molecule, is edited and leaves the nucleus through the large nuclear pores
• Transcription can best be described as synthesis of mRNA.
• Outside the nucleus, ribosome subunits attach to the beginning of the mRNA molecule and begin the process of translation which occurs in the cytoplasm. The end product is protein.
• In translation, tRNA molecules bring specific amino acids, encoded by each mRNA codon, into place at the ribosome site.

Protein Synthesis Steps

• Transcription: mRNA (messenger RNA); happening IN THE NUCLEUS; A process in which an mRNA molecule forms along one gene sequence of a DNA molecule within the cell's nucleus. The end-product is mRNA molecule.
• Translation occurs in the cytoplasm with protein as the end product.

Post-translation Processing

• Chaperone proteins and other enzymes in the cytosol, endoplasmic reticulum (ER), and Golgi apparatus help polypeptides fold then possibly combine into larger protein molecules or hybrid molecules.
• They are capable of properly refolding an improperly refolded protein molecule.
• Proteome: The complete set of proteins synthesized by a cell and destroys improperly folded protein.
• Human proteome: all the proteins synthesized in the body.
• One human cell is estimated to synthesize thousands of different enzymes.

Cell Growth

• Newly formed cells produce a variety of molecules and other structures necessary for growth by using the information contained in the genes of DNA molecules.
• This stage is known as interphase (INTERPHASE IS NOT A PART OF MITOSIS).
• Interphase = new growth.
• One of the two major phases of the cell life cycle is the growth phase, including growth phase 1 (G1) and growth phase 2 (G2).
• All the structural proteins, plus enzymes needed to make lipids, carbohydrates, and other substances, are made by the cell with information in the genes of DNA molecules.

Life Cycle of the Cell

• S = synthesis phase.
• G0 phase: where the non-dividing cells go.
• Mitosis: PMAT.
  • P = Prophase.
  • M = Metaphase.
  • A = Anaphase.
  • T = Telophase.
• Cytokinesis results in two identical daughter cells.
• The processes of growth and reproduction of successive generations of cells follow a cyclic pattern from newly formed, growing to maturity by synthesizing new molecules and organelles (G1 and G2 phases), including the replication of an extra set of DNA molecules (S phase) in anticipation of reproduction.
• Mature cells reproduce (M phase) first by distributing the two identical sets of DNA (produced during the S phase) in the orderly process of mitosis, and then by splitting the plasma membrane, cytoplasm, and organelles of the parent cell into two distinct daughter cells (cytokinesis).
• Daughter cells that do not go onto reproduce are in a maintenance phase (G0).
• All the structural proteins, plus the enzymes needed to make lipids, carbs, and other substances, are made by the cell with information in the genes of DNA molecules.
• Mitochondria often replicate themselves during the cell growth phase so that their total number is very large the time the cell is ready to reproduce.
• The two new strands are called chromatids of chromosomes.
• Chromatids are attached pairs; the point of attachment is called the centromere.
• Centromeres hold two newly replicated strands together.

Cell Reproduction (M Phase):

• Cells reproduce by splitting into two separate cells through cytokinesis, the splitting of the plasma membrane and cytoplasm.

Mitosis

• Mitotic cell division: the process of organizing and distributing nuclear DNA during cell division has four distinct phases.
• Prophase is the "before phase" which occurs After interphase, and the nuclear envelope falls apart as the chromatids coil up to form chromosomes that are joined at the centromere.
• As chromosomes form, centrosomes (centrioles/aster) move away from eachother toward the poles of the parent cell and spindle fibers are constructed between them.
• Interphase is when the cell is not experiencing mitosis (that is, during the growth phase between cell divisions), it is said to be in interphase, meaning “between phase”.
• Metaphase literally means “position changing phase” or in the middle phase” with the chromosomes moved by the cytoskeleton into an orderly pattern that is aligned along a plane at the “equator” of the cell.
• Anaphase means “apart phase” where the centromere of each chromosome splits to form two chromosomes, each consisting of aa single DNA molecule.
• Telophase means “end phase” and sees DNA return to its original form and location within the cell.
• After completion of telophase, each daughter cell begins interphase to develop into a mature cell.
• Cleavage furrow comes apparent in telophase (but actually starts in anaphase).

Summarized Mitotic Cell Division

• During interphase, division begins at the end of interphase (G2), after the cell has already replicated the DNA in its nucleus and increased its cytoplasm sufficiently for division.
• During prophase, chromosomes form from the nuclear chromatin material as the nuclear envelope disappears.
• During metaphase, chromosomes line up along the cell’s equatorial plate, with spindle fibers distinctly visible on either side.
• During anaphase, spindle fibers pull each of the two chromatids (now called chromosomes) toward opposite poles of the cell.
• During telophase, chromosomes are now at opposite poles, nuclear envelopes begin forming around each group, and the cleavage furrow of cytokinesis becomes apparent.
• After mitosis and cytokinesis are complete, the two daughter cells begin the first growth (G1) of interphase. When they are ready, each daughter cell may continue the life cycle by undergoing mitotic division.

Meiosis

• Meiosis is a type of cell division that occurs only in primitive sex cells during the process of becoming mature sex cells where:
  • Spermatogonia and oogonia be become mature sex cells called gametes (sperm and ova).
  • Total of 46 chromosomes (diploid) in body cells.
  • Total of 23 chromosomes (haploid) in sex cells, so that when sperm meet ovum, the total is 46.
• Sex cells have a haploid number of chromosomes because the end result of fertilization is the fusion of two gametes, each containing the haploid number of (23) chromosomes. Fertilization results in the formation of a zygote, which is a diploid cell having 46 chromosomes, 23 from each parent. The zygote is the first cell of the human offspring.
• Meiotic cell division takes place in two steps: meiosis 1 and meiosis 2.
• Meiosis 1 is called reduction division because of the number of chromosomes is reduced by half (from the diploid number to the haploid number).
• Different types of cells have different life cycles.
• Advancing age creates changes in cell numbers and in their ability to function effectively.
• Examples of decreased functional ability include muscle atrophy, loss of elasticity of the skin, and changes in the cardiovascular, respiratory and skeletal systems.
• Most cell processes occur at the same time in all cells through the body.
• The processes of normal cell function result from the coordination dictated by the genetic code.

Tissue

• A group of similar cells that perform a common function where the matrix is non living intercellular material.
• 4 principle types of tissue:
  • Epithelial tissue.
  • Connective tissue.
  • Muscle tissue.
  • Nervous tissue: least able to regenerate.
  • Neuropathy:
    • Chemo induced.
    • Diabetic.
    • Idiopathic.
• Embryonic development of tissues results in three primary germ layers:
  • Endoderm: the innermost layer of cells or tissue of an embryo in early development.
  • Mesoderm: the middle layer of an embryo in early development.
  • Ectoderm: the most exterior layer of cells or tissue.
• Extracellular Matric (ECM) is a complex nonliving fluid material between cells in a tissue where:
  • Some tissues have a large amount, some have hardly any.
  • Different kinds of components give ECM in different tissues a variety of characteristics.
• Components:
  • Water.
  • Proteins.
• Structural proteins
  • Collagen – strong, flexible protein fiber.
  • Elastin – elastic fibers.
• In skeletal muscles: mostly a network of structural protein fibers in the EXM that holds skeletal muscle tissue together.
• Some tissues, the ECM does not bind to the tissues cells (the fluid nature of the bloods matric (plasma) does not hold blood tissues in a solid mass at all.

Tissue Repair

• Varying capacity for repair:
  • Can regenerate: phagocytotic cells remove dead or injured cells, and gaps are filled in with new tissue.
  • Can be replaced by scar tissue.
    • Keloid; thick scar that develops in the lower layer of skin.
    • Keloids are caused by too much collagen being produced after we suffer an injury
  • Greatest capacity for regeneration: epithelial and connective tissue.
  • Limited capacity to regenerate: muscle and nerve tissues.

Body Membranes

• Cover and protect body surface.
• Line body cavities or cover internal organs.
• Cover inner surfaces of hollow organs.
• Anchor organs to each other or to bones.
• Secrete lubricating fluids.
• Two major types:
  • Epithelial membranes.
  • Connective tissue membranes.
• Membrane: thin sheetlike structure that may have many important functions in the body.
• Lubrication reduces friction (in lungs and in the heart).
• Epithelial membranes vs connective tissues:
  • Epithelial; composed of epithelial tissues glued by a basement membrane to an underlying layer of supportive connective tissue.
  • Connective: composed exclusively of various types of connective tissue; no epithelial cells are present.
• Epithelial:
  • Mucous.
  • Cutaneous.
  • Serous.
    • Parietal: the outer lining of the organ.
    • Visceral: tells you its LINING an organ.

Tumors and Cancer

• Neoplasm: any abnormal cell growth.
• Growths can be benign or malignant
• Three types of tissue tumors:
  • Epithelial.
  • Connective.
  • Miscellaneous.
• Factors that may lead to cancer:
  • Genetic factors.
  • Carcinogens (sometimes called mutagens).
  • Age.
  • Metabolic factors.

Cancer Detection and Treatment:

• Self-examination.
• Medical imaging.
• Blood tests.
• Biopsy.
• Chemotherapy and radiation.
• Laser therapy and immunotherapy.