Post on 23-Feb-2016
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Chapter 3Cells & Their Functions
The Role of Cells• Basic unit of all life• Cytology – the study of cells• Simplest structure that shows all the
characteristics of life such as–Organization–Metabolism–Responsiveness–Homeostasis–Growth –Reproduction
The Role of Cells• It is possible for a single cell to live
independently of other cells–Protozoa–bacteria
• Cells make up all tissues• All activities of the human body result from
the activities of individual cells
Microscopes• Stains – dyes that color cells and
tissues to aid viewing• Compound light microscope
– Magnifies 1000 times– 2 lenses– Uses visible light for illumination
• Transmission electron microscope– 1,000,000 times magnification– Uses electron beam instead of
light• Scanning electron microscope
– 100,000 times magnification– Shows surface features, but in 3D
view
Cell Structure
• All cells share certain characteristics.
• Main parts:– Plasma membrane– Nucleus– Cytoplasm– Organelles
Plasma Membrane
• Formerly called the cell membrane
• Function– Encloses the cell– Participates in growth
& reproduction– Involved in cellular
interactions– Regulates what
enters and leaves the cell
Plasma Membrane
• Bilayer structure – Phospholipids – Cholesterol– Carbohydrates– Proteins
• Channels • Transporters• Receptors• Enzymes • Linkers• Cell identity markers
Plasma Membrane Proteins• Channels pores that allow specific ions to enter or leave• Transporters shuttle substances across the membrane• Receptors act as points of attachment for materials that act
on the cell• Enzymes participate in reactions occurring at the plasma
membrane• Linkers give structure to the membrane and help cells attach
to each other• Cell identity markers are proteins that are unique to an
individual’s cells. Important in immunity & tissue transplants
Cell Nucleus
• Nucleus is the biggest organelle in the cell• Organelles – specialized structures that
perform different tasks for the cells• Control center of the cell• Contains chromosomes which govern all
cellular activities• Nucleolus contains RNA, DNA, and proteins
and manufactures ribosomes in the cytoplasm• Almost all DNA is found in the cell nucleus
The Cytoplasm
Cytosol – liquid part of cytoplasm containing nutrients and organelles such as:
• Endoplasmic reticulum• Ribosomes• Mitochondria• Golgi apparatus• Lysosomes• Peroxisomes• Vesicles• Centrioles
• Endoplasmic reticulum Network of membranes that is either smooth or
rough• Smooth ER – involved in lipid synthesis• Rough ER – comes from ribosomes attached
to the ER • Ribosomes – necessary for protein synthesis and
are either attached to ER or floating free
Cell Organelles Cont.• Mitochondria – converts nutrients into ATP,
the power plant of the cell. Active cells have more mitochondria than other cells
• Golgi Apparatus – involved in sorting and modifying proteins and then packaging them for export from the cell
• Centrioles - near the nucleus; help to organize the cell and divide the cell contents during the process of cell division
Cell Organelles Cont.• Lysosomes – remove waste and
foreign materials from the cells• Peroxisomes – destroy byproducts of
metabolism • Vesicles – storage units of the cell,
can also move materials into and out of cells
Surface Organelles• Cilia – small hair-like projections that
wave, creating movement of fluids around the cell. Respiratory passage cells have cilia and cells in the female reproductive tract.• Flagellum – long whip-like extension
for movement. The only cells in humans with flagella are sperm cells.
Cellular Diversity• Size –Average size is 10-15 micrometers–RBCs are small – 7 micrometers–Muscle cells are big – 200 micrometers
• Composition – most human cells have all the organelles. Some cells have more than one type of organelles than another due to their function
Protein Synthesis: Chromosomes & Genes
• Chromosomes are the hereditary units that govern cells– 23 pair, 46 total
• Divided into genes• Genes carry the
messages for the development of particular inherited characteristics and do so by directing the manufacture of proteins in the cell.
DNA & RNA
• Genes are made of DNA – deoxyribonucleic acid –DNA is composed of nucleotides
• RNA – Ribonucleic acid – a related compound which participates in protein synthesis but is not part of chromosomes–RNA is composed of nucleotides
DNA & RNA Composition
• DNA is composed of – 4 nucleotides
• Adenine (A)• Guanine (G)• Cytosine (C)• Thymine (T)
• RNA is composed of – 4 nucleotides
• Adenine (A)• Guanine (G)• Cytosine (C)• Uracil (U)
Nucleotide Structure
• Composed of three units
• Sugar – – RNA – ribose– DNA - deoxyribose
• Phosphate - an area containing phosphorus
• Nitrogen base – an area containing nitrogen
Deoxyribose & Ribose
DNA Structure• DNA is built like a ladder
– Sugar-phosphate backbone– Nitrogen bases are the steps
• 2 DNA strands make a pair – Nucleotide adenine always
pairs with thymine– Guanine always pairs with
cytosine
• 2 DNA strands are bonded together with hydrogen bonds – form double helix
RNA
• RNA interprets the information from the DNA blueprint to synthesize proteins
• RNA is found almost entirely in the cytoplasm• RNA is a single strand of nucleotides• There are 3 types of RNA– mRNA – messenger RNA– rRNA – ribosomal RNA– tRNA – transfer RNA
The Role of RNA
Protein synthesis• Transcription – Messenger RNA (mRNA)
• Translation– Transfer RNA (tRNA)– Ribosomal RNA (rRNA)
Protein Synthesis and RNA• DNA breaks its bonds and
uncoil into single strand• Transcription – transfer of
information from DNA to mRNA in the nucleus >> matching RNA strand forms based on pairing
• mRNA leaves the nucleus and travels to a ribosome in the cytoplasm
Transcription.
Translation.
Cell Division• Meiosis– Sex cells
• Mitosis– Somatic cells
Cell Division - Mitosis• Mitosis – the process of cell division where an
original parent cell becomes two identical daughter cells
• Before mitosis can occur, DNA must double – therefore, the 46 chromosomes in the nucleus must double
Interphase• The stage of life in a cell between one mitosis and the next• During this phase, DNA uncoils and each strand takes on a
matching strand of nucleotides to make up 2 new DNA strands, each one identical to the original and each other
• The new, uncoiled DNA strandsare held in the centromere until mitosis• A typical cell spends most of its cycle in interphase and a relatively short time in mitosis
Mitosis
• 4 stages• Prophase• Metaphase• Anaphase• Telophase
Mitosis - Prophase• The new double strands of DNA coil tightly
into a double helix • The nucleolus and the nuclear membrane
begin to disappear• All other organelles disappear except those
needed for mitosis• Two centrioles in the cytoplasm move
towards opposite ends of the cell• Thin spindle fibers begin to form between
the centrioles
Mitosis - Metaphase
Chromosomes attach to spindle fibers and line up across the center of the cell
Mitosis - Anaphase
The centromere splits and the duplicatedchromosomes separate and begin to move
towards opposite ends of the cell
Mitosis - Telophase
• A membrane appears around each group of separated chromosomes, forming 2 new nuclei
• The plasma membrane pinches off to divide the cell
Mitosis : Summary• At the end of mitosis
there 2 new cells • Each daughter cell has
exactly the same DNA as the original
• All organelles reappear in the daughter cells
Movement of Substances Across the Plasma Membrane
Travel across the membrane is based on several factors:
• Molecular size• Solubility• Electrical charge
Movement That Does Not Require Cellular Energy
Passive transport • Diffusion• Osmosis• Filtration• Facilitated diffusion
Diffusion
• Concentration gradient - constant movement of particles from a region of higher concentration to one of lower concentration
• Equilibrium - diffusing substances spread throughout available space until their concentration is equal everywhere
• Passage is limited to those particles small enough to pass through spaces between molecules of the plasma membrane
Osmosis• The diffusion of water through a semi-
permeable membrane • Water moves from an area where there is
more water molecules to an area where there is less water molecules
• The solvent water moves from an area of lower solute concentration to an area of higher solute concentration
• Water follows salt
Osmotic Pressure
• Describes the tendency of a solution to draw water into it– Directly related to concentration: the higher the
concentration of a solution, the greater the tendency to draw water in
• A measure of the force driving osmosis– Determined by applying enough pressure to the
surface of a liquid to stop the flow of water by osmosis
Filtration
• Passage of water containing dissolved materials through a membrane as a result of a “pushing” force on one side– Movement of materials out of the capillaries and
into the tissues under the force of blood pressure– Movement of materials out of the blood and into
urine in the kidneys
Facilitated Diffusion
• Movement of materials across the plasma membrane in the direction of the concentration gradient but using transporters to move the material at a faster rate– Glucose
Movement That Requires Cellular Energy
Active transport• Bulk transport or vesicular transport– Endocytosis• Phagocytosis• Pinocytosis
– Exocytosis
Active Transport
• Moves solute particles in or out of the cell opposite of the direction they would normally flow by diffusion
• Transporters – proteins in the plasma membrane that are required to transport the particles– Nerve and muscle cells depend on active transport
of Na, K and Ca for proper function
• Endocytosis – bulk transport of large quantities of materials into or out of the cells– Phagocytosis – large particles are engulfed by the
plasma membrane and moved into the cell• White blood cells rid the body of foreign materials
– Pinocytosis – cell membrane engulfs droplets of fluid
How Osmosis Affects Cells• Isotonic – solutions with concentrations equal to the
concentration of the cytoplasm– Blood plasma, interstitial fluid, normal saline (0.9% salt),
5% dextrose• Hypotonic – a solution less concentrated than intracellular
fluid– A cell in hypotonic solution will draw water in and may
burst– Hemolysis – a red blood cell drawing too much water in
and bursting• Hypertonic – a solution more concentrated than intracellular
fluid– Crenation – the process by which a cell that loses water to
surrounding fluids and shrinks
Cell Aging
As cells multiply, changes occur that may lead to their damage or death•Free radical injury•Enzyme injury•Gene alteration or mutation•Slowing cell activity•Apoptosis
Cells and Cancer
Certain mutations may cause changes in cells• Uncontrolled reproduction of cells• Cells spread (metastasize), producing cancer• Cancer cells form tumors, crowding out
normal cells