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84 Cards in this Set
- Front
- Back
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The Cell
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The cell is the basic structural and functional unit of life
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Survival of a living organism
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Depends on the individual and collective activity of cells
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All Cells
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Come from pre-existing cells, they cannot be manufactured
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200 types of human cells
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The human body has trillions of cells, they come in a variety of shapes and sizes
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Size and Shape
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related to function
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All cells are interdependent upon each other
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While each cell is able to function independently, it constantly receives signals from other cells – helps to coordinate function of the cells
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Three primary parts to most cells
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Plasma membrane - the skin
Cytoplasm - the body Nucleus – the control center |
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cells that connect body parts
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fibroblasts, Epithelial cells, Erythrocytes
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Cells that move body parts and organs
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Smooth and skeletal
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Cells that store nutrients
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Fat cells
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Cells that fight diseases
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Macrophages
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Cells that gather info and control body functions
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nerve cells
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Cells of reproduction
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Sperm Cells
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Structure of a Generalized Cell
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While types of cells may appear to be quite different, they contain many structures which are common to nearly all cells
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Plasma Membrane:
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*The plasma membrane separates a cell from its surrounding environment.
*Acts as the “skin” of the cell *Separates intracellular fluid from extracellular fluid *Transports materials – nutrients, wastes, metabolic products – in and out of cell |
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Everything that enters and leaves a cell is regulated by its plasma membrane
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Changing the plasma membrane will disrupt the cell’s normal function – can be beneficial (meds) or detrimental (toxins)
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The Lipid Bilayer
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All plasma membranes consist of a bilayer of lipids
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Phospholipids
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compose about 50% of the membrane
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Phospholipids
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Each has a hydrophobic, non- polar, and hydrophilic, ionized end
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Cholesterol
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20% of all membrane lipid
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Glycolipids
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lipids with a bound carbohydrate (glyco)
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Proteins
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Imbedded in the, about 50% of membrane – numerous functions
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Functions of Membrane Proteins
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Transport
*Receptors for signal transduction *Attachment to cytoskeleton and extracellular matrix *Source of cellular identification - Glycocalyx – ‘sugar coating” provides specific biological markers ex. sperm-egg, immune cells-bacteria *Enzymatic activity |
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Transport
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A protein that spans the membrane
may provide a hydrophilic channel across the membrane that is selective for a particular solute. *Some transport proteins hydrolyze ATP as an energy source to actively pump substances across the membrane. |
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Receptors for signal transduction
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A membrane protein exposed to the
outside of the cell may have a binding site with a specific shape that fits the shape of a chemical messenger, such as a hormone. The external signal may cause a change in shape in the protein that initiates a chain of chemical reactions in the cell. |
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Attachment to the cytoskeleton
and extracellular matrix (ECM |
Elements of the cytoskeleton (cell’s
internal supports) and the extracellular matrix (fibers and other substances outside the cell) may be anchored to membrane proteins, which help maintain cell shape and fix the location of certain membrane proteins. Others play a role in cell movement or bind adjacent cells together. |
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Glycoprotein
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Some glycoproteins (proteins bonded
to short chains of sugars) serve as identification tags that are specifically recognized by other cells. Glycocalyx |
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Enzymatic activity
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A protein built into the membrane may
be an enzyme with its active site exposed to substances in the adjacent solution. In some cases, several enzymes in a membrane act as a team that catalyzes sequential steps of a metabolic pathway as indicated (left to right) here. |
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Membrane Junctions – Cell to Cell “Joints”
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Three types:
Tight junction Desmosome Gap junction |
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Tight Junctions
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Prevent fluids and most molecules from moving between cells
Where might these be useful in the body? Ex: Digestive tract – esp. stomach – HCl in stomach – if leaked out, could destroy adjacent tissues Tight junctions: Impermeable junctions prevent molecules from passing through the intercellular space |
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Desmosomes
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“Rivets” or “spot-welds” that anchor cells together. Where might these be useful in the body? Areas of great mechanical stress - skin – our primary protective barrier, heart muscle – can’t afford to “pull” our heart muscle as we can a hamstring.
(b) Desmosomes: Anchoring junctions bind adjacent cells together and help form an internal tension-reducing network of fibers – reduces chance of tearing - Important in tissues that face a lot of mechanical stress such as skin and heart muscle |
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Gap Junctions
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allow small molecules to pass from cell to cell
For spread of ions between cardiac or smooth muscle cells – helps synchronize their electrical activity and contractions ) Gap junctions: Communicating junctions allow ions and small molecules to pass from one cell to the next for intercellular communication |
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Concept of Selective Permeability
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The plasma membrane is selectively or differencially permeable
Some substances easily cross the lipid membrane Some cross the membrane with assistance from protein carriers Some simply can not cross the membrane Example: substances that are unable to pass across membranes are not absorbed by the digestive tract i.e. polysaccharides - celluloses |
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Cellulose
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is an organic compound ….a polysaccharide
Cellulose is the most common organic compound on Earth |
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Passive transport
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no energy (ATP) required, flows down concentration gradient
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Diffusion
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movement of a solute
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Osmosis
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movement of a solvent
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Active transport
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requires energy expenditure (ATP) on the part of the cell
Can work against concentration gradients |
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Diffusion
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Movement from an area of high concentration to an area of low concentration
Simple diffusion Involves movement of solutes Substances pass directly through the lipid bilayer or through channel proteins Includes nonpolar and lipid-soluble substances |
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Facilitated Diffusion
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Used by certain polar molecules including sugars, ions and amino acids that are unable to pass through the lipid bilayer
These substances use carrier proteins or pass through protein channels (always from high to low concentration)Carrier-mediated facilitated diffusion via a protein carrier specific for one chemical; binding of substrate causes shape change in transport protein |
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Osmosis
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Diffusion of a solvent across a semipermeable membrane – in humans, the solvent is water
Despite being polar, water readily crosses lipid bilayers passively (no energy required) Occurs when the concentration of water differs on opposite sides of a membrane. This only occurs when the amount of solute is different on each side A molecule of solute will displace a water molecule, changing the concentration of water ex: 1 part solute – H20 concentration goes to 99%.) Osmosis, diffusion of a solvent such as water through a specific channel protein (aquaporin) or through the lipid bilayer |
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Tonicity
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think of it as the trigger for Osmosis.the ability of a solute to cause a change in water movement across a membrane
May cause a cell to either shrink or swell. Isotonic - Solutions with the same solute concentration as that of the cytosol…they result in no movement – there is therefore NO net change in water across the membrane |
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Hypertonic
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Solutions having greater solute concentration than that of the cytosol
Water is drawn out of cell |
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Hypotonic
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Solutions having lesser solute concentration than that of the cytosol
Water is drawn into cell |
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Active Processes
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Requires carrier proteins
Requires ATP as an energy source to move substances across a membrane Substance can be moved AGAINST its concentration gradient Two types – Active transport and Vesicular transport |
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Active Transport: Sodium-Potassium Pump
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The concentration of K+ is 30-50x higher inside the cell
The concentration of Na+ is 30-50x higher outside the cell If simple diffusion ruled, K+ would leave, and Na+ would enter, until they reached equilibrium The Na-K pump couples the removal of sodium, with the entry of potassium The protein in the membrane that accomplishes this is an enzyme: Na+-K+ ATPase The electrochemical gradients maintained by the Na K pump are crucial for cardiac & skeletal muscle function and for neuron function. |
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Vesicular Transport
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Transport of large particles and macromolecules across plasma membranes inside membranous sacs called vesicles – hence the name
Requires energy (ATP) – remember, it’s active |
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Exocytosis
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Moves substances from interior of the cell to exterior of cell - extracellular space
Ex: hormone secretion, waste excretion |
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Endocytosis
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Enables large particles and macromolecules to enter the cell
Plasma membrane infolds, bringing extracellular fluid and solutes into the interior of the cell Phagocytosis – pseudopods (amoeboid movement) engulf solids and bring them into the cell’s interior Important for removal of dead cells – the release of cellular contents can trigger inflammation or undesirable immune responses – autoimmune diseases i.e. RA, Lupus |
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Roles of Membrane Receptors
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Cell Signaling/Recognition
A way for cells to communicate with their environment Can be by physical or chemical contact Allows cells to recognize foreign items molecules, bacteria, viruses, etc. Messages are received to perform specific functions, e.g. secrete a hormone or generate a nerve impulse |
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Cytoplasm
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Cytoplasm – all material between plasma membrane and the nucleus.
Cytosol Organelles Inclusions |
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Cytosol
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largely water with dissolved proteins, salts, sugars, and other solutes
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Organelles
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metabolic machinery of the cell – ex: mitochondria, ribosomes, endoplasmic reticulum, etc.
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Inclusions
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chemical substances present in some cells - ex: glycogen granules (liver, muscle cells), lipid droplets (fat cells), melanin (skin cells)
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Mitochondria
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Cellular energy factories - generate most of the cell’s ATP
Cells heavily involved in energy production have the most mitochondria – cardiac, skeletal muscle cells Contain their own DNA and RNA Can reproduce themselves – fission – pinch in halves – grow to former size |
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Ribosomes
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Granules containing protein plus rRNA (ribosomal RNA)
Sites of protein synthesis Two basic types: Free floating – produce soluble proteins that work in cytosol Membrane bound – produce proteins for cell membrane or export from cell |
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ER - Rough & Smooth
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Rough ER
External surface studded with ribosomes Manufactures all secreted proteins Responsible for the synthesis of membrane proteins and phospholipids Smooth ER Does not synthesize proteins Involved primarily in in lipid metabolism |
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Golgi Apparatus
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Consists of stacked and flattened membranous sacs – associated with zillions of tiny membranous vesicles
Acts as the main “traffic director” for cellular proteins Major function is to modify, concentrate and package proteins made at the ER |
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Lysosomes
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Spherical membranous organelles containing digestive enzymes - abundant in phagocytes
Digest bacteria, viruses, and toxins that have entered the cell Provide a safe place for intracellular digestion – contain the dangerous digestive enzymes that could digest the cytoplasmic components if enzymes not contained ex: overdose of Vit.A - lysosomal membrane breaks down, releases digestive enzymes Breakdown bone to release Ca - when Ca is needed for other metabolic processes such as nerve impulse conduction - bone is a dynamic Ca storage site Involved in some developmental processes such as interdigital web disintegration during fetal growth, and destruction of expendable tissues such as uterine lining during menstrual cycle Secretory lysosomes are found in white blood cells (leukocytes), immune cells (lymphocytes), and melanocytes (pigment cells) |
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Peroxisomes
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Membranous sacs containing a variety of powerful enzymes including oxidases
Neutralize dangerous free radicals – highly reactive chemicals with unpaired electrons (i.e., O2–) Detoxify harmful or toxic substances such as alcohol or formaldehyde Peroxisomes abundant in organs involved in detoxification processes – liver, kidneys |
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Cytoskeleton
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The “skeleton” of the cell
Elaborate series of rods running through the cytosol Consists of, microfilaments, and intermediate filaments, microtubules |
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Centrioles
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Small barrel-shaped organelles located in the centrosome near the nucleus
Pinwheel array of microtubules Involved with mitosis Form the bases of cilia and flagella |
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Microvilli
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Tiny fingerlike extensions of the plasma membrane that act to increase
surface area dramatically Found most commonly are absorptive cells such as intestinal and kidney tubule cells |
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Nucleus
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Contains nuclear envelope, nucleoli, and chromatin
Control center of the cell Contains the genetic library (DNA) with blueprints for all cellular proteins |
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Nucleus Notes
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Most cells have one nucleus
Some have multiple nuclei – Multinucleate - Muscle cells, osteoclasts (bone destruction cells), some liver cells One type of cell has no nucleus – Anucleate - mature erythrocytes (RBCs) because they lack a nucleus and DNA, they cannot reproduce or produce proteins for cellular repair– they float around in blood stream 3-4 months, then breakdown Average nucleus is spherical – about 5 um diameter |
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Interphase
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Growth (G1),
synthesis (S), growth (G2) |
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Mitotic phase
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Mitosis and cytokinesis
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G1
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This is the phase in which cells do their routine functions
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G0
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Only present in cells that permanently cease dividing ex: nerve, heart
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S
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DNA is replicated – 23 pairs becomes 46 pairs – to provide full complement of DNA in each new daughter cell
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G2
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Rapid preparation for division
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DNA Replication
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DNA helix unwinds
Helicase untwists the double helix and exposes complementary strands Each nucleotide strand serves as a template for building a new complementary strand DNA polymerase adds complementary nucleotides to make multiple, short, new strands DNA ligase splices together the short segments to make one long strand |
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Cell Division
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Essential for body growth and tissue repair
Mitosis - Division of the nucleus From the Special Note Dept: One type of cell division where DNA is not replicated – Meiosis –formation of gametes – sperm and ovum – they have 1/2 the normal complement 23 pairs of chromosomes ie. 23 unpaired chromosomes Cytokinesis - Division of the cytoplasm |
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Phases of mitosis
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Prophase
Metaphase Anaphase Telophase |
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Prophase
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Signals the beginning of cell division
Chromosomes become visible Centriole pairs separate and the mitotic spindle is formed |
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Metaphase
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Chromosomes cluster at the middle of the cell with their centromeres aligned at the equator
This arrangement of chromosomes along a plane midway between the poles is called the metaphase plate |
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Anaphase
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Centromeres of the chromosomes split
Chromosomes are pulled toward poles |
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Telophase and Cytokinesis
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The two new sets of chromosomes extend into chromatin
New nuclear membrane is formed from the rough ER Nucleoli reappear Spindle apparatus breaks down and disappears |
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From DNA to Protein
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DNA has the instructions for all cell activities, but it needs a way to carry them out
All actions in the cell are accomplished by proteins How do the instructions get from the DNA to the proteins? |
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It happens by Transcription
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Transfer of information from DNA to RNA
Messenger RNA (mRNA) carries the genetic information from DNA in the nucleus to the ribosomes in the cytoplasm |
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RNA Polymerase
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Enzyme that makes the mRNA strand m = messenger
Recognizes a start signal that tells the enzyme where to begin Unwinds the DNA template Adds bases to the mRNA strand that are complementary to those on the DNA template Recognizes a termination signal to stop transcription |
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Translation
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Making a protein from the mRNA strand
Keep in mind the RNA strand contains the instructions from a gene on the DNA DNA serves as the master blueprint for protein synthesis Translation occurs in the cytoplasm, on ribosomes Ribosomal RNA (rRNA) is a structural component of ribosomes The mRNA attaches to the ribosome to begin translation |
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From mRNA to Proteins
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mRNA consists of a long chain of nucleotides, but proteins consist of long chains of amino acids.
How is the message in nucleotides converted to a chain of amino acids? The Genetic Code |
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Developmental Aspects of Cells
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All cells of the body contain the same DNA but develop into all the specialized cells of the body
Genes of specific cells are turned on or off Cell specialization is determined by the kind of proteins that are made in that cell Development of specific and distinctive features in cells is called cell differentiation |
