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Chapter 6
A Tour of the Cell
Basic Definitions
 A cell is the basic unit of life.
All living things are made of
cells.
 Inside cells are organelles,
which are small, membrane
bound structures that have
specific jobs.
 Cells are small because
nutrients and water must be
able to get to all parts of the
cell (low surface area to
volume ratio)
Eukaryotic vs. Prokaryotic
 A prokaryotic cell does NOT have a
nucleus or membrane bound
organelles. It is small and simple,
having only cytoplasm (fluid) and
ribosomes (organelles that make
protein). Bacteria are prokaryotic.
 A eukaryotic cell DOES have a
nucleus and organelles. They are
larger and more complex, and include
plants and animals.
Subcellular terms
 Cytoplasm or cytosol is the fluid inside a cell.
 All cells are surrounded by cell (plasma) membranes,
which are selectively permeable.
Organelles
 The nucleus contains the genes (DNA) of an organism. It is the
control center of the cell.
 DNA is organized into chromosomes, structures that carry genes.
 Chromosomes are made of chromatin, a combination of DNA and
protein.
Organelles
 The nucleus is surrounded by a membrane called the
nuclear membrane.
 Inside the nucleus is the nucleolus, which makes
ribosomes.
 Ribosomes are the organelles that make proteins.
The endomembrane system
 Several organelles make up the endomembrane
system, which help make and transport substances.
 Vesicles are tiny vehicles that shuttle things around the
endomembrane system.
Endomembrane: the ER
 The endoplasmic reticulum is a series of membranes that make up
almost half of the cell.
 There are two types:
 Rough ER: has ribosomes on the surface; makes proteins and
membranes
 Smooth ER: has no ribosomes on it; makes lipids, carbs,
enzymes, and detoxifies drugs and poisons.
Endomembrane
 The Golgi Apparatus (Golgi Body) is like the cell’s UPS:
it manufactures, stores, sorts, and ships products made
by the ER to other parts of the cell.
Endomembrane
 Lysosomes are sacs of enzymes that an animal cell
uses to digest macromolecules (pH 5).
 If they pop, cells digest themselves. This is called
apoptosis, and is programmed cell death.
Endomembrane
 Vacuoles are large, hollow organelles. They can be
 Food vacuoles: used to store and digest cellular food
 Contractile vacuoles: pump excess water from cells, help
propel them through liquid
 Central vacuole: found in plant cells, store water. Are
surrounded by a membrane called the tonoplast.
Review of the
Endomembrane System
Energy Organelles
 The mitochondria is found in
plant and animal cells. It is the
site of cellular respiration, the
power house of the cell, and
makes energy (ATP) from
sugar and oxygen.
 Inner membrane is called the
cristae
 Inside the cristae is a
compartment called the matrix.
Energy Organelles
 The chloroplast is found ONLY in plant cells, it converts
light energy into chemical energy (ATP).
 The fluid in the chloroplast is called the stroma
 Thylakoids (look like poker chips) are stacked in piles
called grana
Energy Organelles
 Peroxisomes contain enzymes that transfer hydrogen
from various substances to oxygen, makes hydrogen
peroxide H2O2.
 These break down fatty acids and detoxify poisons
The Cytoskeleton
 The cytoskeleton is made up of a network of fibers and
helps organize and give structure to cells.
Cytoskeleton: Microtubules
 Microtubules are hollow tubes
that help maintain cell shape,
help cells move, help
chromosomes move during cell
division, and help organelles
move inside cells.
 The centrosome and centrioles
help move chromosomes
 Flagella are long tails, cilia are
short hair-like projections, both
move cells
Cytoskeleton: microfilaments
 Microfilaments are double stranded filaments that help
maintain cell shape, are involved in muscle contraction,
and help cells divide and move.
 Actin is a protein that helps muscles move
Cytoskeleton: intermediate
filaments
 Intermediate filaments are proteins coiled into thick
cables. They help anchor organelles in place
Outside the Cell
 Plant cells have cell walls made of cellulose. They
protect and support the cell, and regulate water
balance.
 Plasmodesmata are holes in cell walls that allow water
and nutrients to be exchanged.
 Animal cells have intercellular junctions for this function