CHAPTER 4: A TOUR OF THE CELL
-Every cell has a plasma membrane forming its outside border and setting it off from its fluid environment.
Plasma membrane
-enables to take up needed molecules
-site where important reactions occur
-disposes wastes
-maintains 'good' molecules inside the cell
Cytoplasm: the semifluid inside
a cell
Organelle: a cellular structure
4.1 Microscopes Provide Windows to the World of the Cell
Light microscope (LM)
-uses light
-LM 109X
-magnify up to 1000 times
Resolving power - measure clarity of image (2 separate objects)
Electron microscope (EM)
-uses a beam of electrons
-1/1,000,000 mm = 1nm
-magnify 100,000 times
2 kinds of electron microscope:
-samples maintained in vacuum chamber
-no air
-cannot be used with living samples
-scanning electron microscope (SEM)
-architecture of cell surfaces
-help discover cell structure details-transmission electron microscope (TEM)
-internal cell structure
-thin sections
4.2 Cell Sizes Vary with their Function
Smallest cells:
-bacteria mycoplasmas
-diameters 0.1-1.0 µm (1µm = 10-6m or 1/10,000 cm)
Plants and animal cell avg 10-100 µm or 1/100 cm
Bulkiest cells: bird eggs
Longest cells: certain muscle and nerve cells
Cell size and shape related to function
-Ex:bird egg, nerve cell, red blood cell
4.3 Natural Laws Limit Cell Size
Cell must be able to house (minimum size):
-DNA
-protein molecules
-internal structures to serve and reproduce
Cell must be able to (max size is limited):
-have adequate nutrients
-dispose of wastes
Big cells less surface area
Cells shapes:
-cubes
-spheres
-very long (nerve cells) and thin
4.4 Prokaryotic Cells are Small and Structurally Simple
-Bacteria and Archaea are prokaryotic cells
-All other forms of life are eukaryotic cells
-Prokaryotic cell:
-1/10 size of typical eukaryotic
-lacks nucleus
-DNA coiled into a nucleoid region; Ribosomes
-plasma membrane encloses cytoplasm
-fairly rigid and chemically complex cell wall
-protects
-maintain shape
-Some bacteria has a capsule:
-sticky outer coat
-surrounds the cell wall
-further protects the cell surface
-help glue bacteria to surfaces
-sticks
-rocks
-fast-flowing streams
-tissues within the human body
Some bacteria have another structure:
-pili (singular, pilus) to attachment
-flagella (singular, flagellum) to movement
4.5 Eukaryotic Cells are Partitioned into Functional Compartments
-Very different from prokaryotic cells
-much more complex
-membranous organelles:-nucleus
-endoplasmic reticulum
-Golgi apparatus
-mitochondria
-lysosomes
-peroxisomes
-Cellular metabolism occur in the fluid filled spaces within membranes
-Internal membranes increase total area & provide surface for metabolic processes
-Most organelles found in cells of animals and plants
-exception lysosomes, not found in plants
Other differences between plant and animal cells:
-animal cells have a pair of centrioles, plants don't
-animal cells may have flagellum, different from bacteria (function, structure)
Plant cell:
-rigid rather thick cell wall – for protection & shape
-polysaccharide cellulose
-chloroplasts
-photosynthesis
-large central vacuole
-contains enzymes (lysosome in animals)
-take up water helping enlargement
-centrioles, flagellum, cytoskeleton
-nonmebranous structures
-microtubules (protein tubes) made of proteins
-Ribosomes in the cytoplasm
-protein synthesis (animals and plants) in the ER
4.6 The Nucleus is the Cell's Genetic Control Center
Nucleus = Genetic control center
-houses DNA
-directs all cell activities
-is attached to proteins-chromatin
-chromosomes
-can be seen with light microscope
-within the nuclear envelope
-chromatin DNA + RNA of fibers
-nucleolus (mass of fibers and granules) adjoining the chromatin
-where ribosomes are made
4.7 Overview: Many Cell Organelles are Related Through the Endomembrane
System
-Eukaryotic organelles
-endomembrane system: cytoplasmic network of membranes, some connected and some not
-synthesize, store, and export chemicals
-Endoplasmic reticulum (ER): (ex of direct interrelations as part of the endomembrane system) interconnected folded membranes that form an extensive network throughout the cytoplasm
-sometimes continuos with nuclear envelop and/ or plasma membrane
4.8 Rough Edoplasmic Reticulum Makes Membrane and Proteins
-Rough ER- ribosomes on the
surface (proteins made)
-make more membrane
-ribosomes make proteins
-secretory protein or antibody (glycoprotein transport vesicle travels to Golgi finished transp vesicle travel to plasma membrane)
-Smooth ER – no ribosomes
-enzymes in the membrane
-synthesis functions of lipids, steroids, fatty acids, and phospholipids
-ovaries: estrogen (ER of ovary cells)
-liver: detoxify, breakdown drugs, etc. (enzyme on ER of liver regulate sugar
release)
-storage of calcium for muscle tissue
-muscle cell triggers the release
-When liver cells respond to drugs: as cells are exposed the amt of smooth ER & its enzymes to detoxify increase
body tolerance to drugs-higher & higher doses required to achieve or particular effect such as redation.
4.9 Smooth Endoplasmic Reticulum has a Variety of Functions
-is continuous with rough ER
-has enzymes embedded in its membrane
-most important function:
-synthesis of lipids (fatty acids, phospholipids and steroids)
-ex: smooth ER of ovaries and testes synthesize steroid sex hormones
-smooth ER of liver cells:
-certain enzymes help regulate the amount of sugar released from liver into bloodstream
-other enzymes help breakdown drugs (sedatives, stimulants and certain antibiotics) and other harmful substances
-complications:
-liver cells exposed to these chemicals
-amounts of smooth ER and its enzymes increase => increasing body tolerance to drugs => higher and higher doses are necessary to achieve a particular effect
-another function:
-smooth ER stores calcium ions (those are necessary in muscle for contraction) => when a nerve signal stimulates a muscle cell, calcium ions leak from smooth ER into the cytoplasma fluid, where they trigger contraction of the cell.
4.10 The Golgi Apparatus Finishes, Sorts and Ships Cell Products
Golgi apparatus is made of a stack of flattened membrane sacks. Works closely with the ER.
-each organelle can have from few to hundreds of stacks (the number is related to the cell activity)
Functions of the Golgi:
4.11 Lysosomes Digest Cell's Food and Wastes
4.12 Abnormal Lysosomes can Cause Fatal Diseases
These diseases are hereditary (transmitted from parents to children) and are called Lysosome storage diseases
Two diseases:
4.13 Vacuoles Function in the General Maintenance of the Cell
Vacuoles are membranous sacs that belong to the endomembrane system
-vacuoles have different shapes, sizes, and functions
Ex: food vacuole collaborates with lysosome to digest food
Plants don't have lysosomes. Plants have a central vacuole:
4.14 A Review of the Endomembrane System
Transport vesicles made by ER & Golgi develop into the lysosomes & vacuoles that carry out digestion of other processes in the cell.
4.15 Chloroplasts Convert Solar Energy to Chemical Energy
4.16 Mitochondria Harvest Chemical Energy from Food
Mitochondria:
4.17 The Cells Internal Skeleton Helps Organize its Structure
and Activities
Cytoskeleton is a supportive meshwork of fine fibers (it is the skeleton of the cytoplasm)
Cytoskeleton is made of:
4.18 Cilia and Flagella Move when Microtubules Bend
4.19 Cell Surfaces Protect, Support and Join Cells
Cells interact with their environments and with each other via their surface
Plant cells are supported by rigid cell walls made of cellulose
Animal cells are more flexible and covered with polysaccharides and proteins
To function in a coordinate way as part of a tissue, the cells must have cell junctions -structures that connect them to one another
4.20 Eukaryotic Organelles Comprise Four Functional Categories
-manufacture
-breakdown
-energy processing
-support, movement, and communication between cells
4.21 All Life Forms Share Fundamental Features