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Ch. 6 - CELLS
3 principles of modern cell theory:
1. Every living organism is made up of one or more cells.
2. The smallest living organisms are single cells, and cells are the functional
units of multicellular organisms.
3. All cells arise from preexisting cells.
Cells range from 1 - 100 micrometers
How we study cells
The cell is as fundamental to Biology as the atom is to chemistry. All
organisms are made of cells.
COMPOUND LIGHT MICROSCOPE – Visible light is passed through a
specimen and then through glass lenses. The lenses refract (bend) the light.
Magnification – is how much larger the object appears compared to its
real size.
Resolution – is a measure of the clarity of the image.
Light microscopes can magnify to about 1000 X the size of the actual specimen.
A typical body cell can range between 1 – 100 micrometers. (1 mm = 1000
micrometers) Organelles are too small to be seen through this instrument.
ELECTRON MICROSCOPE – instead of using visible light, a beam of electrons
are emitted through the specimen. Electron beams have much shorter
wavelength than the wavelengths of visible light. There are 2 basic kinds:
TEM/ transmission electron microscope – the TEM aims an electron beam
through a thin section of the specimen. They use electromagnets as lenses to
focus and magnify the image by bending the paths of the electrons. Cell
biologists use this instrument to study internal structures of cells.
SEM/ scanning electron microscope – is useful for the study of the surface
of the specimen. The electron beam scans the surface of the sample, which is
usually coated with a thin film of gold.
Both electron microscopes have the disadvantage of having to kill the cells
during preparation of specimens.
Isolating organelles – The goal of Cell Fractionation is to take cells apart. The
instrument used to separate cell part is the centrifuge. The most powerful
(ultracentrifuge) can spin as fast as 80,000 rpm / and apply forces on particle
500,000 times the force of gravity.
Why cells are not large – depends on the surface area to volume ratio. Cells
need to be able to communicate and if they increase in volume too much it
makes this task impossible. If a cell gets 10 times larger then its surface area
increases by a factor of 100 times which increases the volume by 1000 times.
See table on next page
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Total surface area
(height x width x
number of sides x
number of boxes)
Total volume
(height x width x
length x number of
boxes)
Surface area to
Volume ratio
(area / volume)
6
150
750
1
125
125
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1.2
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Prokaryotic cells (before nucleus) – has its genetic material (DNA) concentrated
in a region called the NUCLEOID, but no membrane separates this region from
the rest of the cell. These cells are full of Ribosomes where proteins are
synthesized. Outside the plasma membrane are a rigid cell wall and often an
outer capsule, usually jellylike. Some bacteria have Flagella (locomotion
organelles).
The cell wall is composed of peptidoglycan (polymers of sugar) that is
cross linked by short polypeptide units. No eukaryotes possess cell wall with this
composition.
Examples of this type of cell would be bacteria, including cyanobacteria
Bacteria – gram staining to ID types. (+) purple, thick single layered cell wall. (-)
red, multi-layered wall / more complex.
Jelly like substance is long chain of sugars called polysaccharides.
Most Prokaryotes have no membrane-bounded organelles.
ANIMAL cells – the most prominent organelle in an animal cell is usually the
Nucleus. Chromatin in the nucleus consists of DNA. Adjoining part of the
chromatin in the nucleus are one or more nucleoli (singular – nucleolus) Nucleoli
are involved in production of particles called Ribosomes, which synthesize
proteins. Nucleus is bordered by a porous envelope consisting of two
membranes. Most of the cells metabolic activities occur in Cytoplasm. The
cytoplasm is full of specialized organelles suspended in a semi-fluid medium
called a cytosol. Occupying most of the cytosol is the ER (Endoplasmic
reticulum). There are 2 forms, rough & smooth. The Golgi apparatus consists of
flattened sacs active in the synthesis, refinement, storage, sorting, and secretion
of a variety of chemicals products. Other membrane enclosed organelles are:
Lysosomes, which contain mixtures of digestive enzymes. Perisomes, a diverse
group of organelles containing enzymes that perform specialized metabolic
processes. Vacuoles, which have a variety of storage and metabolic functions.
Mitochondria (singular – mitochondrion) carry out cellular respiration, which
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generates ATP from organic fuels such as sugar. Non membranous organelles
within the cells include microtubules, microfilaments and centrioles.
PLANT cells – like the animal cell, a plant cell is surrounded by a plasma
membrane and contains a nucleus, ribosomes, ER, Golgi apparatus,
mitochondria, peroxisomes, and microfilaments & microtubules. However, a
plant cell also contains a family of membrane enclosed organelles called
Plastids. The most important type of plastid is a Chloroplast, which carries out
photosynthesis. Another prominent organelles a large central vacuole. The
vacuole stores chemicals, breaks down macromolecules and plays a large part
in plant growth. The vacuole membrane is called the tonoplast. Outside a plants
plasma membrane is a thick cell wall, which helps maintain the cell’s shape and
protects the cell.
Cells have 3 components:
Plasma membrane (functions)
It isolates the cytoplasm from the external environment.
It regulates the flow of materials between the
cytoplasm & its environment.
It allows interaction with other cells.
Genetic material
DNA
Cytoplasm
Consists of all the material inside the plasma membrane (water, salts,
assortment of organic molecules, enzymes, other proteins used in
structure, and organelles)
Types of cells:
Prokaryotic “Before nucleus”
<5micrometers
Eukaryotic “True nucleus”
>10 micrometers
most have a rigid cell wall
(some have polysaccharide coating)
plants = cell wall
animal = no cell wall
cytoplasm is relatively
homogenous
cytoplasm composed of
many organelles, fluid
called cytosol (cell solution
Nucleus - Looks like a “woofle ball”, porous.
Contains the DNA, and inside area called a nucleolus.
Pores - allow for water, ions, and ATP to pass through freely
large molecules are controlled, however exert extreme selectivity of RNA
molecules. The pores have proteins within the holes that go between the nuclear
envelope
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Nuclear envelope - outer surface peppered w/ribosomes.
Some places ER is directly continuous with outer membrane.
DNA is wrapped into tight packages called CHROMOSOMES (we will talk more
in detail at a later time)
Nucleolus(-li) singular - contains ribosomal RNA, & proteins
Cell Membrane - all membranes composed of a Phospholipid bi-layer with
proteins (synthesized in ER)
& cholesterol imbedded in between.
Cholesterol = structural framework
Proteins = transportation of molecules, catalyzing chemical reactions, and
connecting membranes.
Organelles w/ endomembrane system - ER, Golgi bodies, lysosomes.
Functions in processing & synthesis of proteins and other substances - require
an interconnected system for transportation, synthesis, & modification. Only
Eukaryotes
ER or Endoplasmic reticulum - system of membranous tubes, sacs forming
compartments.
Rough ER (w/ribosomes) - concerned with protein synthesis & transport.
Polypeptide chains made, moved into CISTERNAL spacing, where chains are
folded - carbohydrates & lipids attach to them. Sacs are pinched off sent to Golgi
bodies, smooth ER (further modification), plasma membrane (release content),
storage vesicles within cytoplasm.
Smooth ER (no ribosomes) - some accept & modify proteins sent from rough ER,
but others function in break down of glycogen or fat molecules. Is also mostly
associated with lipid production such as plant seeds, intestinal cells
(triglycerides), cells of adrenal cortex (steroid hormones).
Skeletal muscle cells have highly specialized smooth ER sarcoplasmic reticulum
, arranged collar like around contractile units of muscle cells. Calcium stored &
released to function in signal transmission between nerve & muscle cells.
Golgi complex - set of smooth membranes that are stacked into flattened, fluid
filled sacs. The side closest to the plasma membrane - bulges at the ends. It’s
derived from the ER. Each stack is a golgi body. (in plants called dictyosome)
3 functions:
1 Separates proteins & lipids received from ER.
2 Modifies some molecules - sugars to proteins to
make glycoproteins.
3 Packages fore mentioned materials into vesicles
for transport to cell membrane or other parts of cell.
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Main links between organelles (nucleus, ER, golgi bodies, cell membrane)
assembly, modification, transport, and storage or secretion.
Lysosome - major function of this organelle is in digestion and disposal. Each
organelle contains ~40 hydrolytic enzymes that are able to break down
polysaccharides, DNA, RNA, proteins, and certain lipids.
Membranes keep enzymes isolated. They are constantly being taken apart and
repaired. Defective organelles.
Microbodies - are membranous containers for different enzymes that take part in
a range of conversion reactions.
They form as buds that break away from rough ER.
Plastids - are organelles specialized in photosynthetic food production and
storage. There are 3 main kinds:
Chloroplasts - with photosynthetic pigments and starch
storage capacity.
Chromoplasts - with pigments that are not functioning in
photosynthesis. These pigments are red or
brown; they give carrots, fruits, petals their
distinct color.
Amyloplasts - with starch storing capacity, no pigments.
They are colorless. They occur in stems,
roots, seeds & other parts that have little
sunlight. Ex. Abundant in potato cells.
Chloroplasts - organelles specializing in photosynthesis. They are doublemembrane with the inner membrane containing a semi-fluid matrix called
stroma. Within the stroma are sacs called thylakoid discs, stacked into piles of
discs which are called grana (granum-singular).
Membranes of granum are sites where sunlight is trapped and where ATP is
formed. The stroma is where the ATP energy goes into building sugars.
Mitochondria - organelles specializing in production of ATP.
These too are double-membrane with the inner membrane
containing a matrix. With in the cell the inner membrane folds back and forth in
the form of cristae (crista-singular).
Between the inner membrane and outer there is the intermembrane
compartment.
Chloroplasts & Mitochondria are similar:
Both have DNA - (probable remnants of evolution).
Both have enzymes that synthesize ATP.
Both have double membranes.
But… both work completely different.
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Cytoskeleton - internal framework of eukaryotic cells
Cellular contents stream about but are drifting about haphazardly. Proper cell
function requires nonrandom organization. There are complex protein filaments
in varied sizes that maintain the structures, microtubles (thick), intermediate
microfilaments, and microfilaments (thin).
Perform following functions:
1 Cell shape
2 Cell movement
3 Organelle movement
4 Cell division
Microfilaments - Found in cytoplasmic lattices and is a small, flexible strand.
Actin is one of its structural components in association with a second protein
myosin. One filament slides over the next.
Microtubules - is a hollow cylinder assembled from protein subunits called
tubulin. Microtubules are involved in organelle movement, help divide heredity
material during cell division, and are a key part of flagella & cilia.
Many are consistently being assembled and disassembled. Centrioles or
basal bodies are organelles that contain microtubules. They are duplicated
during cell division and assist in the process.
Intermediate filaments - provide a permanent supportive framework that provides
shape to cells and anchor various cell parts together.
Cilia & Flagella - Arise from basal bodies, usually just beneath the plasma
membrane. Basal bodies have 9 short fused triplets around a pair of unfused
microtubules, which give rise to 9 pairs of microtubules.
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