Chapter 4
section 4.2
Parts of a Eukaryotic Cell
Cell Membrane
Cells cannot survive if isolated from their
environment
Both nutrients and wastes must pass
through the cell membrane
Cell membrane is selectively permeable
The structure of the cell membrane
depends on the functions the cell performs
Membrane Lipids
All cell membranes are made primarily of
lipids and proteins
Phospholipids- have a polar hydrophilic
head and two nonpolar hydrophobic tails
The cell membrane is a lipid bilayer
Phospholipids are arranged so that their
heads point outward and the tails are at
the interior
Membrane Proteins
Peripheral proteins- located on the
interior and exterior surface of the cell
membrane
Integral proteins- embedded in the cell
membrane
Some proteins form channels or pores for
substances to pass through
Others bind to a substance on one side of
the membrane and carry it to the other
side
Fluid Mosaic Model
The lipid bilayer behaves more like a fluid
than a solid
Lipids and proteins can move laterally
within the bilayer
Organelles
Cytoplasm- the area between the cell
membrane and the nucleus (contains
organelles)
Cytosol- aqueous fluid inside a cell
Mitochondria
The “powerhouse” of the cell
Sites of chemical reactions that transfer
energy from organic compounds to ATP
Has two membranes: smooth outer
membrane and folded inner membrane
(cristae)
Mitochondria have their own DNA
This supports the Endosymbiont theory
(mitochondria may have been prokaryotic
cells that developed a symbiotic
relationship inside eukaryotic cells)
Ribosomes
Most numerous organelles
Not surrounded by a membrane
Composed of RNA and proteins
Important in the synthesis of proteins
Endoplasmic Reticulum (ER)
A system of membranous tubules and
sacs
Functions as a pathway for molecules to
move from one part of a cell to another
Rough endoplasmic reticulum- covered
with ribosomes (found in cells that make
large amounts of proteins)
Smooth endoplasmic reticulum- no
ribosomes (involved in synthesis of
steroids in gland cells, regulation of
calcium in muscle cells, and breakdown of
toxic substances in the liver)
Golgi Apparatus
The processing, packaging, and secreting
organelle
System of membranes
Modifies proteins for export by the cell
Lysosomes
Small, spherical organelles that enclose
hydrolytic enzymes within single
membranes
Enzymes digest proteins, carbohydrates,
lipids, DNA, RNA, viruses, bacteria, and
old organelles
Common in animal cells
Cytoskeleton
Network of protein strands in the cytosol
that provide support and allows movement
of organelles within the cell
Made up of microfilaments and
microtubules
Microfilaments are made of actin
(function for cell movement and muscle
contraction)
• Microtubules function as spindle fibers
when the cell is about to divide
Cilia and Flagella
Hairlike organelles that extend from the
surface of the cell
Used for movement
Cilia are short and present in large
numbers
Flagella are whiplike and few in number
Cilia and flagella both have nine pairs of
microtubules arranged around a central
pair
Nucleus
Most prominent organelle
Surrounded by a double membrane
(nuclear envelope) perforated with pores
Chromatin is found inside the envelope
Stores hereditary information
Nucleolus
Spherical area inside the nucleus
Site where ribosomes are synthesized
Plant Cells
Have three structures not found in animal
cells: cell walls, vacuoles, and plastids
Cell Wall
Rigid outer area that provides support
Contain long chains of cellulose
Vacuoles
Fluid-filled organelles that store enzymes
and metabolic wastes
Very large
Plastids
Surrounded by two membranes
May store starch or fats or may contain
pigments which absorb visible light
Chloroplast- absorb sunlight and convert it
to chemical energy through
photosynthesis
Chloroplasts contain a series of flattened
sacs called thylakoids
Contain a green pigment