Biology Honors - Chapter 4

cytoskeleton

a network of protein fibers in the cytoplasm of a eukaryotic cell; includes microfilaments, intermediate filaments and microtubules
-provide for structural support as well as movement

understanding of nature often goes hand in hand with

the invention and refinement of instruments that extend our senses

discovery of cells

1665 Robert Hooke used a crude microscope to examine a piece of bark from cork tree: compared structures he saw to rooms in monasteries which were called cells

Antoni van Leeuwenhoek

worked with more refined lenses than Hooke, examined numerous subjects, produced drawings and descriptions of his discoveries

what has vastly expanded our view of the cell

improved microscopes and techniques
ex:
-fluorescently colored stains reveal cytoskeleton in cells

how to see dynamic nature of living cells

look through a microscope or view videos: all parts of a cell are moving and interacting

light microscope

-first microscope
an optical instrument with lenses that refract (bend) visible light to magnify images and project them into a viewer's eye or photographic film

magnification

increase in an object's image size compared with its actual size

most common units of length that biologists use

-meter (m)
-centimeter (cm)
-millimeter (mm)
-micrometer (µm)
-nanometer (nm)

resolution

-important factor in microscopy
-measure of the clarity of an image: ability to distinguish two nearby objects as separate
-each optical instrument has a limit to its resolution
-human limit is as close together as .1 mm

light microscope limits

-resolution limit is .2 micrometer (size of smallest bacterium)
-cannot resolve details of structure of a small cell
-can only effectively magnify objects about 1,000 times

microscope used form 1665 to mid-1900s

light microscope

discoveries made with light microscope

-microorganisms
-animal cells
-plant cells
-some structures within cells
-accumulation of evidence in mid-1800s led to cell theory

cell theory

-every organism exists as one or more cells
-the cell is the smallest unit that has the properties of life
-all cells arise from pre-existing cells
-cells contain hereditary material, which they pass on to their offspring when they divide

electron microscope (EM)

-biologists began using it in 1950s: spurred giant leap forward in cell structure knowledge
a microscope that uses magnets to focus an electron beam through, or onto the surface of, a specimen
-can distinguish biological structures as small as about 2 nm, a hundredfold greater resolution than a light microscope

EM has enabled biologists to explore

cell ultrastructure: complex internal anatomy of a cell

scanning electron microscope (SEM)

a microscope that uses an electron beam to study the surface details of a cell or other specimens, which is usually coated with a thin film of gold: beam excites electrons on surface, electrons detected by a device that translates their pattern into an image projected onto a video screen
-biologists use it to study the detailed architecture of cell surfaces
-3d looking images

transmission electron microscope (TEM)

-used to study the details of internal cell structure
a microscope that uses an electron beam to study the internal structure of thinly sectioned specimens
-coat the specimens in gold

transmission electron microscope (TEM) function

-section is stained with atoms of heavy metals, which attach to certain cellular structures more than others
-electrons scattered by these more dense parts, and image is created by the pattern of transmitted electrons

SEM and TEM lenses

use electromagnets as lenses to bend the paths of the electrons, magnifying and focusing the image onto a monitor

SEM and TEM colors

-initially black and white but are often artificially colorized to highlight or clarify structural features

what can't an electron microscope do

cannot be used to study living specimens because the methods used to prepare the specimen kill the cells

best microscope to study a living process

a light microscope equipped with a video camera

modern adaptations to light microscopy

-differential interference contrast microscopy: optical technique that amplifies differences in density so that structures in living cells appear 3d
-techniques that use fluorescent stains that selectively bind to various cellular molecules

diameter of most cells

between 1 and 100 µm
-only visible with a microscope

minimum cell size

at a minimum, cell must be large enough to house enough DNA, protein molecules and structures to survive and reproduce

maximum cell size

-need to have a surface area large enough to service the volume of a cell
-active cells have a huge amount of traffic across their outer surface: such as essential flow of oxygen, nutrients and wastes

surface-to-volume ratio in cells

-large cells have more surface area than small cells but they have a much smaller surface area relative to their volume than small cells
-when a cell divides the original cell has the same volume as the sum of the volumes of the new smaller cells, but the surface area of the original cell is smaller than the sum of the surface areas of the new smaller cells
-combined smaller cells have a much greater surface to volume ratio than the large cell

plasma membrane

the membrane at the boundary of every cell that acts as a selective barrier to the passage of ions and molecules into and out of the cell; consists of a phospholipid bilayer with embedded proteins
-phospholipids arrange themselves on their own: energetically favorable for them: hiding from water to be more stable

each phospholipid is composed of (include charge and polarity)

-a head with a negatively charged phosphate group
-two non-polar fatty acid tails

phospholipid bilayer

phospholipids group together to form a two layer sheet called a phospholipid bilayer
-hydrophilic heads face outward, exposed to the aqueous solutions on both sides of a membrane
-hydrophobic tails point inward, mingling together and shielded form water

inside of phospholipid bilayer (is it hydro-)

-diverse proteins floating
-regions of the proteins within the center of the membrane are hydrophobic
-exterior sections of the proteins exposed to water are hydrophilic

phospholipid structure and function

acts as "traffic cop" of the cell: non-polar molecules such as O2 and CO2 can easily move across the membrane's hydrophobic interior
-some of the membrane's proteins form channels (tunnels) that shield ions and polar molecules as they pass through the hydrophobic center of the membrane
-other proteins serve as pumps, using energy to actively transport molecules into or out of the cell

prokaryotic cells

a type of cell lacking a membrane-enclosed nucleus and other membrane-enclosed organelles; found only in the domains bacteria and archaea
-first to evolve
-earth's sole inhabitants for more than 1.5 billion years

animal cell diagram

plant cell diagram

eukaryotic cells

a type of cell that has a membrane-enclosed nucleus which houses most of their DNA and membrane-enclosed organelles
-all organisms except bacteria and archaea are composed of eukaryotic cells
-evidence indicates that they evolved from prokaryotic cells about 1.8 billion years ago

three domains of organisms

-Bacteria (prokaryotic)
-Archaea (prokaryotic)
-Eukarya (eukaryotic)

eukaryote vs prokaryote

prokaryote smaller and much simpler in structure

things in all cells (5)

-bounded by a plasma membrane
-cytosol
-one or more chromosomes (DNA)
-ribosomes
-cytoplasm

cytosol

-thick, jellylike fluid
-the semifluid portion of the cytoplasm
-cellular components are suspended in it

chromosome

a gene-carrying structure found in the nucleus of a eukaryotic cell and most visible during mitosis and meiosis; also, the main gene-carrying structure of a prokaryotic cell
-consists of one very long DNA molecule that is packaged around proteins

ribosomes

a cell structure consisting of r(ribosomal)RNA and protein organized into two subunits and functioning as the site of protein synthesis in the cytoplasm
-use instructions from nucleus written in mRNA to build proteins

in eukaryotic cells where are ribosomal subunits constructed

nucleolus

cytoplasm

the contents of a eukaryotic cell between the plasma membrane and the nucleus, consists of a gel-like fluid medium and organelles; can also refer to the interior of a prokaryotic cell

nucleoid

a non-membrane-bounded region in a prokaryotic cell where the DNA is concentrated

significance of difference in ribosomes in prokaryotes vs eukaryotes

in prokaryotes they are smaller and and differ somewhat
-molecular differences are the basis for the action of some antibiotics, which specifically target prokaryotic ribosomes: protein synthesis can be blocked for the bacterium that's invaded you, but not for you, the eukaryote who is taking the drug

prokaryotic cell structure

outside the plasma membrane of most prokaryotes is

a fairly rigid, chemically complex cell wall
-wall protects the cell and helps maintain its shape
-some antibiotics, such as penicillin, prevent the formation of these protective walls: they can kill invading bacteria without harming your cells

capsule

certain prokaryotes have a sticky outer coat called a capsule around the cell wall, helping to glue the cells to surfaces or to other cells in a colony

surface projections

short projections help attach prokaryotes to each other or their substrate

flagella

a long singular appendage specialized for locomotion: propel a cell through its liquid environment
-like cilia, eukaryotic flagella have a "9+2" arrangement of microtubules covered by the cell's plasma membrane

human flagella

sperm

how to see the internal details of cells

electron microscope

size comparison of most pro and eukaryotic cells

most prokaryotic cells are about one-tenth the size of a typical eukaryotic cell

difference between a model of a cell and a real cell

cells have multiple copies of organelles (except nucleus)
-ex: hundreds of mitochondria and millions of ribosomes in one cell, plant cell could have 30 chloroplasts
-cells have different shapes and relative proportions of cell parts, depending on their specialized functions

organelle

"little organ" a membrane-enclosed structure with a specialized function within a cell
-has a lipid and protein composition that suits its function

4 basic functional groups of organelles and other structures of eukaryotic cells

1. nucleus and ribosomes
2. endoplasmic reticulum, Golgi apparatus, lysosomes, vacuoles, and peroxisomes
3. mitochondria and chloroplasts
4. cytoskeleton, plasma membrane and plant cell wall

4 basic functional groups of organelles and other structures of eukaryotic cells: nucleus and ribosomes

carry out the genetic control of the cell

4 basic functional groups of organelles and other structures of eukaryotic cells: endoplasmic reticulum, Golgi apparatus, lysosomes, vacuoles, and peroxisomes

organelles involved in the manufacture, distribution and breakdown of molecules

4 basic functional groups of organelles and other structures of eukaryotic cells: mitochondria and chloroplasts

mitochondria in all cells and mitochondria and chloroplasts in plant cells function in energy processing

4 basic functional groups of organelles and other structures of eukaryotic cells: cytoskeleton, plasma membrane and plant cell wall

structural support, movement and communication between cells

cellular metabolism

all the chemical activities of a cell

essence of function of internal membranes of a cell

petition it into functional compartments in which many of its chemical activities, collectively called the cellular metabolism, take place

what is built into the membranes of organelles

various enzymes essential for metabolic processes
-fluid filled spaces within such compartments are locations where specific chemcial conditions are maintained: conditions vary among organelles and favor metabolic processes occurring ine ach

organelles that are in animal cells but not plant cells

lysosomes and centrosomes

are flagella in animal plant or both

some animal cells have flagella or cilia, among plants, only the sperm cells of a few species have flagella

structures that a plant cell has but an animal cell lacks

-rigid, rather thick cell wall (chemically different from prokaryotic cell walls, they contain the polysaccharide cellulose)
-plasmodesmata
-chloroplast
-large central vacuole

which organisms have cell walls

plants, fungi, algae, some single-cell organisms

plasmodesmata

cytoplasmic channels through cell walls that connect adjacent cells

where does photosynthesis occur

chloroplast in plant cell

central vacuole

in a plant cell, a large membranous sac with diverse roles in growth and storage of chemicals and wastes

non-membraneous structures in eukaryotic cells

-cytoskeleton: composed of different types of protein fibers that extend throughout the cell
-ribosomes are found in the cytosol as well as attached to certain membranes

nucleus

1. an atom's central core, containing protons and neutrons
2. the organelle of a eukaryotic cell that contains the genetic material in the form of chromosomes, made of chromatin

how does DNA control cell's activities

directing protein synthesis

how is DNA organized

structures called chromosomes
-proteins help coil these long DNA molecules

length of DNA in one chromosome

laid end to end would stretch to a length of more than 2m, but must coil up to fit into a nucleus only 5 micrometers in diameter

chromatin

all of the packaged DNA in one cell

how does DNA prepare for cell division

copies itself so each daughter cell can receive an identical set of genetic instructions
-chromatin fibers coil up further, becoming thick enough to be visible with a light microscope

nuclear envelope

double membrane that encloses the nucleus, perforated with pores that regulate traffic with the cytoplasm (and connect with the endoplasmic reticulum)
-each is separate phospholipid bilayer and associated proteins
-control flow of materials into and out of the nucleus

nucleolus

structure within the nucleus where ribosomal RNA is made and assembled with proteins imported from the cytoplasm to make ribosomal subunits

where do ribosomal subunits go

exit nucleus to cytoplasm where they join to form functional ribosomes

mRNA (messenger RNA)

directs protein synthesis
-a transcription of protein-synthesizing instructions written in a gene's DNA
-moves into the cytoplasm, where ribosomes translate it into the amino acid sequences of proteins

cells that make a lot of protein have a large number of

ribosomes
-pancreas that produces digestive enzymes may contain a few million

2 locations ribosomes found in

free ribosomes suspended in cytosol (ex: enzymes that catalyze first steps of sugar breakdown for cellular respiration)
bound ribosomes attached to the outside of the endoplasmic reticulum or nuclear envelope

free bound ribosomes

structurally identical
-can function in either location (cytosol or attached to ER or nuclear envelope) depending on protein they are making

endomembrane system

a network of membranes inside and surrounding a eukaryotic cell, related either through direct physical contact or by the transfer of membranous vesicles

vesicles and a function

a sac made of membrane in the cytoplasm of a eukaryotic cell
-transfer membrane segments between them

endomembrane system includes

-nuclear envelope
-ER
-Golgi apparatus
-lysosomes
-various types of vesicles and vacuoles
-plasma membrane (not exactly an endo (inner) membrane in a physical location, but it is related to the other membranes by the transfer of vesicles)
-many of these organelles interact in synthesis, distribution, storage and export of molecules

largest component of endomembrane system

endoplasmic reticulum
-its membranes are continuous within the nuclear envelope
-when vesicles bud from it, they travel to many other components of the endomembrane system
-prime example of direct and indirect interrelatedness of parts of the endomembrane system

endoplasmic reticulum

an extensive membranous network in a eukaryotic cell, continuous with the outer nuclear membrane and composed of ribosome-studded (rough) and ribosome-free (smooth) regions

endoplasmic means

within the cytoplasm

reticulum means

little net (it is like a network of flattened sacs and tubules)

important aspect of components of endomembrane system

dividing the cell into functional compartments, each of which may require different conditions
-membrane of ER enclose a space separate from the cytosol

how to distinguish smooth and rough ER

superimposed electron micrograph

smooth endoplasmic reticulum

the portion of the endoplasmic reticulum that lacks ribosomes
-thats why it looks flat

rough endoplasmic reticulum

portion of the endoplasmic reticulum with ribosomes attached that make membrane proteins and sory proteins

smooth ER funcitons

-enzymes are important in synthesis of lipids, including oils, phospholipids, and steroids
-storage of calcium ions

example of smooth ER in synthesis of steroids

in vertebrates cells of ovaries and testes synthesize the steroid sex hormones: cells are rich in smooth ER, a structural feature that fits their function by providing ample machinery for steroid synthesis

example of smooth ER in synthesis

liver has large amounts of smooth ER with enzymes that help process drugs alcohol and other harmful substances
-addiction can result if drugs affect the functioning of the smooth ER