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BSC 2010 - Exam I Lectures and Text Pages
• I. Intro to Biology (2-29)
• II. Chemistry of Life
–
Chemistry review (30-46)
–
Water (47-57)
–
Carbon (58-67)
–
Macromolecules (68-91)
• III. Cells and Membranes
–
Cell structure (92-123)
–
Membranes (124-140)
• IV. Introductory Biochemistry
–
Energy and Metabolism (141-159)
–
Cellular Respiration (160-180)
–
Photosynthesis (181-200)
THE CELL – The Fundamental Unit of Life
• Cell Theory
• 1. All organisms consist of one or more cells.
• 2. Cells are the smallest functional unit of life.
• 3. All cells arise from pre-existing cells.
• History of cell theory:
• 1. Robert Hooke - 1665 - first described and named cells, looking
at cork
• 2. Loreza Oken - 1805 - “all life comes from and is made of cells”
• 3. Schleiden & Schwann - 1839 - credit for cell theory
• 4. Virchow - 1855- “cells come from pre-existing cells”
Cell structure is correlated to cellular function
• All cells are related by descent from previous cells.
They have been modified over time by evolution.
Figure 6.1
10 µm
Microscopy and Biochemistry
• Cytology – The Study of Cells
• To study cells, biologists use microscopes and
the tools of biochemistry
Microscopes: used to view cells too small to see with our eyes
Different types of microscopes can be used to
visualize different sized cells and cellular
structures.
10 m
0.1 m
Human height
Length of some
nerve and
muscle cells
Chicken egg
1 cm
Unaided Eye
1m
Frog egg
10 µ m
1µm
100 nm
Most plant
and Animal
cells
Nucleus
Most bacteria
Mitochondrion
Smallest bacteria
Viruses
10 nm
Ribosomes
Proteins
1 nm
Lipids
Small molecules
Figure 6.2
0.1 nm
Atoms
Electron microscope
100 µm
Light microscope
1 mm
Measurements
1 centimeter (cm) = 102 meter (m) = 0.4 inch
1 millimeter (mm) = 10–3 m
1 micrometer (µm) = 10–3 mm = 10–6 m
1 nanometer (nm) = 10–3 mm = 10–9 m
Light Microscopes
• Light microscopes
– Pass visible light through a specimen
– Magnify cellular structures with lenses
Visualization Enhancement
– There are several methods for enhancing
visualization of cellular structures
TECHNIQUE
RESULT
(a) Brightfield (unstained specimen).
Passes light directly through specimen.
Unless cell is naturally pigmented or
artificially stained, image has little
contrast. [Parts (a)–(d) show a
human cheek epithelial cell.]
50 µm
(b) Brightfield (stained specimen).
Staining with various dyes enhances
contrast, but most staining procedures
require that cells be fixed (preserved).
(c) Phase-contrast. Enhances contrast
in unstained cells by amplifying
variations in density within specimen;
especially useful for examining living,
unpigmented cells.
Figure 6.3
Visualization Enhancement
(d) Differential-interference-contrast (Nomarski).
Like phase-contrast microscopy, it uses optical
modifications to exaggerate differences in
density, making the image appear almost 3D.
(e) Fluorescence. Shows the locations of specific
molecules in the cell by tagging the molecules
with fluorescent dyes or antibodies. These
fluorescent substances absorb ultraviolet
radiation and emit visible light, as shown
here in a cell from an artery.
50 µm
(f) Confocal. Uses lasers and special optics for
“optical sectioning” of fluorescently-stained
specimens. Only a single plane of focus is
illuminated; out-of-focus fluorescence above
and below the plane is subtracted by a computer.
A sharp image results, as seen in stained nervous
tissue (top), where nerve cells are green, support
cells are red, and regions of overlap are yellow. A
standard fluorescence micrograph (bottom) of this
relatively thick tissue is blurry.
50 µm
Electron microscopes: focus a beam of electrons through a specimen or onto its surface
• The scanning electron microscope (SEM)
– Provides for detailed study of the surface of a
specimen
TECHNIQUE
RESULTS
1 µm
Cilia
(a) Scanning electron microscopy (SEM). Micrographs taken
with a scanning electron microscope show a 3D image of the
surface of a specimen. This SEM
shows the surface of a cell from a
rabbit trachea (windpipe) covered
with motile organelles called cilia.
Beating of the cilia helps move
inhaled debris upward toward
the throat.
Figure 6.4 (a)
Electron microscopes
• The transmission electron microscope (TEM)
– Provides for detailed study of the internal
ultrastructure of cells
Longitudinal
section of
cilium
(b) Transmission electron microscopy (TEM). A transmission electron
microscope profiles a thin section of a
specimen. Here we see a section through
a tracheal cell, revealing its ultrastructure.
In preparing the TEM, some cilia were cut
along their lengths, creating longitudinal
sections, while other cilia were cut straight
across, creating cross sections.
Figure 6.4 (b)
Cross section
of cilium
1 µm
Isolating Organelles by Cell Fractionation
• Cell fractionation
– Takes cells apart and separates the major organelles
from one another by size and density
• A centrifuge
– Is used to fractionate cells into their
component parts
Cell Fractionation
• First, cells are homogenized
in a blender to break them up.
• The resulting mixture (cell
homogenate) is then centrifuged
at various speeds and durations
to fractionate the cell
components, forming a series of
pellets.
Homogenization
Tissue
cells
1000 g
Homogenate
(1000 times the
force of gravity)
Differential centrifugation
10 min
Supernatant poured
into next tube
20,000 g
20 min
Pellet rich in
nuclei and
cellular debris
Figure 6.5
80,000 g
60 min
150,000 g
3 hr
Pellet rich in
mitochondria
(and chloroplasts if cells
are from a Pellet rich in
plant)
“microsomes”
(pieces of
plasma membranes and
Pellet rich in
cells’ internal ribosomes
membranes)
Cell Fractionation
In original experiments, researchers used microscopy to
identify the organelles in each pellet, establishing a
baseline for further experiments.
In the next series of experiments, researchers used
biochemical methods to determine the metabolic
functions associated with each type of organelle.
Researchers currently use cell fractionation to isolate
particular organelles in order to study further details of
their function.
Features all cells have in common
– They are bounded by a plasma membrane
– They contain a semifluid substance called the
cytosol
– They contain chromosomes
– They all have ribosomes
There are two major cell types
• Prokaryotic
• Eukaryotic
– Eukaryotic cells have internal membranes that
compartmentalize their functions
Prokaryotic cells
• Bacteria and cyanobacteria (blue-green algae);
appeared about 3.5 billion years ago.
a. small, 1-10um
b. usually have a cell wall
c. no membrane-bound organelles
d. no membrane-bound nucleus
e. circular DNA concentrated in nucleoid region
f. have a plasma membrane, cytoplasm, & ribosomes
g. some have outer capsule, pili, and/or flagella
Prokaryotic cells
Pili: attachment structures on
the surface of some prokaryotes
Nucleoid: region where the
cell’s DNA is located (not
enclosed by a membrane)
Ribosomes: organelles that
synthesize proteins
Bacterial
chromosome
(a) A typical
rod-shaped bacterium
Figure 6.6 A, B
Plasma membrane: membrane
enclosing the cytoplasm
Cell wall: rigid structure outside
the plasma membrane
Capsule: jelly-like outer coating
of many prokaryotes
0.5 µm
Flagella: locomotion
organelles of
some bacteria
(b) A thin section through the
bacterium Bacillus coagulans
(TEM)
Eukaryotic cells
• All other living organisms (protists, fungi,
plants, animals); appeared about 2.2 billion
years ago.
a. have membrane-bound organelles
b. larger, 10-100um (limited by surface area/volume
ratio)
c. complex chromosomes
d. true nucleus with a membranous nuclear envelope
Cell size is restricted by metabolic needs
• The logistics of carrying out cellular metabolism
sets limits on the size of cells.
• Cells exchange materials and energy with the
environment. This is accomplished across the
plasma membrane.
A smaller cell
– Has a higher surface area to volume ratio,
which facilitates the exchange of materials into
and out of the cell
Surface area increases while
total volume remains constant
5
1
1
Figure 6.7
Total surface area
(height  width 
number of sides 
number of boxes)
6
150
750
Total volume
(height  width  length
 number of boxes)
1
125
125
Surface-to-volume
ratio
(surface area  volume)
6
12
6
Exchanges with the environment
• The plasma membrane
– Functions as a selective barrier
– Allows sufficient passage of nutrients
and waste
Outside of cell
Carbohydrate side chain
Hydrophilic
region
Inside of cell
0.1 µm
Hydrophobic
region
Figure 6.8 A, B
(a) TEM of a plasma
membrane. The
plasma membrane,
here in a red blood
cell, appears as a
pair of dark bands
separated by a
light band.
Hydrophilic
region
Phospholipid
Proteins
(b) Structure of the plasma membrane
The Origin of Eukaryotic Cells
•
There are 2 evolutionary theories of the origin of eukaryotic cells.
They are both supported by evidence, and they probably both
contributed to the formation of eukaryotic cells.
(For additional info: See chapters 26 and 28)
1. Invagination of cell membranes formed membrane-bound
organelles.
–
Evidence? Small invaginations in modern bacteria, called
mesosomes
2. Endosymbiotic theory (Lynn Margulis, 1967) - one prokaryote ate
another without digesting, and came to live together.
–
Evidence? Mitochondria and chloroplasts have their own DNA as
well as double membranes. They can replicate independently of cell
division.
Advantages of membrane-bound organelles
•
1. partitions the cell into compartments
•
2. unique chemistry in different compartments
•
3. participate in metabolic reactions (membranes themselves have
enzymes embedded)
•
4. provides localized environment with conditions for metabolism
•
5. sequesters reactions so they don’t interfere with other reactions in
the cell
Processes cells undergo that allow for multicellularity
• 1. Specialization of cells into specific types
allows for the formation of different tissues.
• 2. Differentiation: the process leading to
specialized cells with different functions.
A Panoramic View of the Eukaryotic Cell
• Eukaryotic cells
– Have extensive and elaborately arranged
internal membranes, which form organelles
• Plant and animal cells
– Have most of the same organelles
An Animal Cell
ENDOPLASMIC RETICULUM (ER)
Rough ER
Smooth ER
Nuclear envelope
Nucleolus
NUCLEUS
Chromatin
Flagelium
Plasma membrane
Centrosome
CYTOSKELETON
Microfilaments
Intermediate filaments
Ribosomes
Microtubules
Microvilli
Golgi apparatus
Peroxisome
Figure 6.9
Mitochondrion
Lysosome
In animal cells but not plant cells:
Lysosomes
Centrioles
Flagella (in some plant sperm)
A Plant Cell
Nuclear envelope
Nucleolus
Chromatin
NUCLEUS
Centrosome
Rough
endoplasmic
reticulum Smooth
endoplasmic
reticulum
Ribosomes (small brwon dots)
Central vacuole
Tonoplast
Golgi apparatus
Microfilaments
Intermediate
filaments
CYTOSKELETON
Microtubules
Mitochondrion
Peroxisome
Plasma membrane
Chloroplast
Cell wall
Plasmodesmata
Wall of adjacent cell
Figure 6.9
In plant cells but not animal cells:
Chloroplasts
Central vacuole and tonoplast
Cell wall
Plasmodesmata
Basic Parts of a Eukaryotic Cell
• All eukaryotic cells have:
– A nucleus
– Cytoplasm – everything outside the nucleus
but still inside the plasma membrane, includes
various cytoplasmic organelles.
– A plasma membrane
The Nucleus: Genetic Library of the Cell
• The nucleus
– Contains most of the genes in the
eukaryotic cell in the form of chromosomes
• Chromosomes are made of chromatin (DNA and
proteins).
– Has a double membrane with pores in it
– Has dense regions called nucleoli - where
ribosome subunits are made
The Nucleus
• The nuclear envelope
– Encloses the nucleus, separating its contents
from the cytoplasm
Nucleus
1 µm
Nucleolus
Chromatin
Nucleus
Nuclear envelope:
Inner membrane
Outer membrane
Nuclear pore
Pore
complex
Rough ER
Surface of nuclear
envelope.
1 µm
Ribosome
0.25 µm
Close-up of
nuclear
envelope
Figure 6.10
Pore complexes (TEM).
Nuclear lamina (TEM).
Ribosomes: Protein Factories in the Cell
• Ribosomes
– Are particles made of ribosomal RNA and protein
– Function in protein synthesis
– Are not membrane bound (also found in prokaryotic
cells)
– Subunits are created in the nucleoli, but assembled in
the cytoplasm.
– use mRNA and translate the genetic code into amino
acids, building proteins. This process is translation
and happens in the cytoplasm.
2 Types of Ribosomes
•
Free ribosomes- make proteins that stay in the cytoplasm and are
used there.
•
Bound ribosomes- make proteins for export or for membrane
construction.
Endoplasmic reticulum (ER)
ER
Ribosomes
Cytosol
Free ribosomes
Bound ribosomes
Large
subunit
0.5 µm
Figure 6.11
TEM showing ER and ribosomes
Small
subunit
Diagram of a ribosome
The Endomembrane System
The endomembrane system regulates protein
traffic and performs metabolic functions in the
cell.
• The endomembrane system
– May have evolved as an invagination of the
plasma membrane
– Includes many different structures
• Nuclear envelope, endoplasmic reticulum, Golgi
apparatus, lysosomes, vacuoles and the plasma
membrane.
The Endoplasmic Reticulum: Biosynthetic Factory
• The endoplasmic reticulum
(ER)
– Accounts for more than half
the total membrane in many
eukaryotic cells
– Is a membranous network
enclosing the lumen or
cisternal space.
– The ER membrane is
continuous with the outer
nuclear membrane.
Figure 6.12
Smooth ER
Rough ER
Nuclear
envelope
ER lumen
Cisternae
Ribosomes
Transitional ER
Transport vesicle
Smooth ER
Rough ER 200 µm
Two Distinct Regions of ER
– Smooth ER, which lacks
ribosomes
– Rough ER, which has
ribosomes embedded in the
membrane
Smooth ER
Rough ER
Nuclear
envelope
ER lumen
Cisternae
Ribosomes
Transitional ER
Transport vesicle
Smooth ER
Rough ER 200 µm
Figure 6.12
Functions of Smooth ER
• The smooth ER
– Synthesizes lipids
– Metabolizes carbohydrates
– Stores calcium
– Detoxifies poison
Functions of Rough ER
• The rough ER
– Has bound ribosomes
– Produces peptide hormones, secretory
proteins, and membranes, which are
distributed by transport vesicles