Download Biology 102 Lecture 5: Cells

10/5/2015
The Cell
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Biology 102
Fundamental unit of life
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Smallest unit that displays all the basic
elements of life
Lecture 5: Cells
Cell Theory
1. All living things are made of one or more cells
Cell Theory
3. Each new cell arises from the division of
another, prepre-existing cell
Cell Theory
2. The simplest organisms are made of only one
cell; the cell is the functional unit of
multicellular organisms
Cell Theory
3. Each new cell arises from the division of
another, prepre-existing cell
Bacteria
Drosophila
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Cell Types
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Two broad categories
Prokaryotes
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Unicellular
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Prokaryotes
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All cells identical – no specialized function
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Eukaryotes
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Lack nucleus, other membranemembrane-bound organelles
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Example: bacteria
Eukaryotes
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May be unicellular
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Eukaryotes
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Examples: yeast, amoebas
May be multicellular
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Examples: plants, animals
Eukaryotic Cells
Eukaryotic Cells
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Differ greatly in appearance and function
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Differ greatly in appearance and function
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4 basic components in common
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4 basic components in common
1.
Plasma membrane
2. Cytoplasm
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Isolation
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Protection
cell but outside the
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Sensitivity
nucleus
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Support
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Gatekeeper
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Material inside the
Contains the cytosol
and organelles
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Eukaryotic Cells
Eukaryotic Cells
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Differ greatly in appearance and function
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Differ greatly in appearance and function
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4 basic components in common
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4 basic components in common
3. The nucleus
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4. Organelles
Control center – the
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“Organs” of the cell
“brain of the cell”
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Perform specific
Contains the DNA
functions
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Some bound by
membranes
Cytoplasm
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Everything inside the membrane, except the
nucleus
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Includes…
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Cell Size
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Cells are small, but molecules for their chemical
reactions are much smaller
A LOT more on the membrane later
Utah Genetics
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Cytosol = liquid portion
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Organelles
Cell Size
Glucose is 108 times smaller than a bacterium
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Reactants needed for metabolism are present in
low concentrations
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Low concentration means reactants don’t collide
often
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This makes chemical reactions slow
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Concentration gets lower as cells get bigger
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What happens to chemical reaction rate in cells
as cells get bigger?
Relative Rate of Reaction
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Cell Size
Cell Size
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Cell Size
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Why prokaryotic cells stay small
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Eukaryotic cells have found a way around this:
membrane--bound organelles
membrane
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Serve to concentrate reactants in appropriate
compartments
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Improves cell efficiency
Cell Size
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This means eukaryotic cells can be larger than
prokaryotic cells
Cell Size
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Still, being small has some advantages
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Solutes taken into cells through membrane
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Consider 2 cubes (even though most cells are
spherical)…
1 µm
Cell Size
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Complete the following calculations:
Cell 1
Cell 2
Surface Area: length x width x 6
Volume: length x width x height
Surface Area/Volume
2 µm
1 µm
Cell Size
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Which cell has the greater surface area?
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Which cell has the greater volume?
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Which cell has the greater ratio of surface area
to volume?
2 µm
Cell Size
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Volume increases faster than surface area
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(x3 vs x2)
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So as cells get bigger, the proportion of surface
area decreases
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Keeps cells small
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Cells need surface area to absorb solutes
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Less surface area = fewer reactions
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Organelles
Non--membranous
Non
Membranous
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Cell wall
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Cytoskeleton
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Cellular extensions
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Cell Membrane
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Endomembrane system
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Vacuoles
Microvilli
Double Membrane
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Cilia
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Nucleus
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Flagella
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Mitochondria
Ribosomes
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Plastids
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All cells are surrounded by a cell membrane
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Consists of a bilayer made of mostly
phospholipids
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Critical to cell function
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Discussed in great detail later
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Also called a plasma membrane
Chloroplasts
Cell Wall
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Cell Wall
Plants, fungi, and bacteria are also have cell walls
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Animal cells do not
Made of polysaccharides secreted through
plasma membrane
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All have a cell membrane
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Non--living
Non
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Exterior to cell
Cell
Membrane
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Cell walls of adjacent plant cells stuck together
with pectin
Cell Wall
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Porous
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Oxygen, carbon dioxide, water carrying small
molecules flow through freely
Cell Wall
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Adds strength and integrity to cells
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Plants, fungi don’t have bones
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Allows them to withstand
gravity and wind and grow upright
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Cytoskeleton
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Internal protein network of cells
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Stabilize cell’s 33-dimensional shape
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Guide vesicles
Microtubules
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Formed from tubulin subunits
1. Component of cytoskeleton – cell shape,
anchor organelles
Microtubules
Microtubules
2. Intracellular transport with motor proteins
3. Move chromosomes during cell division
Microtubules
4. Basis of cellular extensions
Intermediate Filaments
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>60 different kinds
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Resist stretching
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Functions:
1. Strength
2. Stabilize
organelle
position
3. Transport
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Microfilaments
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Made of actin subunits
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Associated with cell movement, changes in cell
shape
Comparison of Cytoskeletal Proteins
Cellular Extensions
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Cilia
Cellular Extensions
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Flagella
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Whip--like
Whip
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Substantially longer than cilia
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Move substances in one direction across
stationary cells
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Only example in human body: sperm
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Example: trachea
Cellular Extensions
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Microvilli
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Very small, highly numerous
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Increase absorptive surface area
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Example: small intestine
Ribosomes
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Site of protein synthesis
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Abundant in cells that produce a lot of protein
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Example: human liver cells have on average
13 million ribosomes in each cell!
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Ribosomes
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Made from rRNA (2 units) and proteins
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Polypeptide chain constructed using information
provided by mRNA
Ribosomes
Many ribosomes can read the same strand of
mRNA at once
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mRNA
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Contains information for…
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Amino acid sequence
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Final destination of protein
mRNA
Final destination of protein
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mRNA
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Final destination of protein somewhere else =
mRNA/ribosome complex associates with
Bound for cytosol
cytosol,, = binds to free ribosome
Endomembrane System
Elaborate system of membranes used to make
and move proteins in a cell
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endomembrane system
Oraganelles Used
Final Destination of Protein
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Rough ER
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Outside cell
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Vesicles
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Within cell membrane
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Golgi apparatus
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Lysosome
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Cell membrane
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Lysosome
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Endoplasmic Reticulum
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Collection of membranous tubes and envelopes
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2 forms
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Endoplasmic Reticulum
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Rough endoplasmic reticulum
(rER
rER))
Smooth endoplasmic reticulum (sER
(sER))
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Site of lipid synthesis, detoxification
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Abundant in liver, kidney, endocrine glands
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Gateway to endomembrane
system
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Studded with ribosomes
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Proteins made by ribosomes
enter rER through pore
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Portion of rER pinches off
to encapsulate protein in a
transport vesicle
Endomembrane System
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Some vesicles stay in cytoplasm
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Others migrate to the Golgi apparatus
Golgi Apparatus
Cis face =
Receiving face
Transport vesicle
Trans face =
Shipping face
Golgi Apparatus
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Proteins are modified and/or combined in the
Golgi, encapsulated and transported to…
1.
Secretory vesicles
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Proteins for discharge from cell
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Examples: insulin, antibodies
Vesicles bound
for elsewhere
Golgi Apparatus
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Proteins are modified and/or combined in the
Golgi, encapsulated and transported to…
2. Cell membrane components
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Example: glycoproteins
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Golgi Apparatus
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Proteins are modified and/or combined in the
Golgi, encapsulated and transported to…
3. Lysosomes
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Cytosolically--active vesicles
Cytosolically
Lysosomes
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Contain more than 50 enzymes
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pH of ~4.5
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Break down almost any biomolecule
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Cell’s “garbage disposal”
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Can fuse with other membranemembrane-defined
structures and release contents
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Lysosome storage diseases (>30)
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Example: TayTay-Sachs disease
Endomembrane System
Vacuoles
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Membranous, fluidfluid-filled sacks
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Most cells contain one or more
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Animal cells have small ones
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Plant cells typically have one large, central one
(may have other, small ones as well)
Animal Cell
Plant Cell
Roug
h
Vacuoles
Vacuoles
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Play a role in maintaining cell integrity
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Regulate cell’s water content
central vacuole fills
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Example: Paramecia have contractile vacuoles
that expel water that leaks in through cell
membrane
with water to
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Example: Plant’s
generate
turgor pressure
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Vacuoles
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Storage site in plants
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Waste that can’t be excreted
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Poisonous compounds
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Amino acids, sugars
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Pigment (flowers)
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Nucleus
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Control center of cell
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Surrounded by nuclear envelope
Makes some plants poisonous, taste bad
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Double membrane
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Covered with pores
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Water, ions pass
through freely
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Ribosomes stud outer
membrane
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Continuous with
endomembrane system
Nucleus
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Contains chromatin
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DNA and associated
Nucleus
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mRNA made in nucleus
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Exits through nuclear
proteins
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pores
Contains all
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Finds ribosomes
instructions for
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Translated into protein
building cell’s proteins
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in the cytoplasm
Dictates types,
amounts of proteins
to be made
Nucleus
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Contains nucleolus
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Site of ribosome
synthesis
Mitochondria
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Site of ATP synthesis – “powerhouse of cell”
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Double membrane (inner and outer)
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Outer membrane is smooth
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Inner membrane has deep folds called cristae
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Mitochondria
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Carry own DNA
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Make some of their own protein (contain
ribosomes)
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Only cellular site to use molecular oxygen
Mitochondria
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Provide energy = most abundant in cells that
need a lot of energy
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Compare: sperm vs cartilage
Plastids
Chloroplasts
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Contained ONLY photosynthetic organisms
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Highly specialized plastid
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Primarily used for storage
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Site of photosynthesis
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Contains
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Pigments (fruit)
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Starch
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Stroma (fluid)
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Thylakoids (membranous sacks)
Chloroplasts
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Thylakoids contain a pigment called chlorophyll
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Gives plants green color
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Captures energy from sunlight
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Transfers energy to other molecules
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Energy used to drive photosynthesis
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Sugar is made from CO2 and H2O
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