biology. cell structure. cell theory every living organism is made up of one or more cells the...
TRANSCRIPT
BIOLOGY.
Cell Structure
Cell Theory Every living organism is made up of
one or more cells The smallest living organisms are
single cells Cells are the functional units of multi-
cellular organisms All cells arise from preexisting cells
Cell Structure Basic Features of All Cells Features of Prokaryotic Cells Features of Eukaryotic Cells
Cells Share Certain Basic Features A cell membrane Nucleic acid A cytoplasm Ribosomes
CELLll Membrane
Function of Cell Membrane Isolates the cell’s contents from external
environment Regulates the flow of materials into and
out of the cell (i.e. selectively permeable )
Allows interaction among cells
Structure of the Cell MembraneFluid-Mosaic Model Consists of phospholipids and proteins The head region of each phospholipid
molecule “loves” water (i.e. is hydrophilic)
The tail region of each phospholipid “hates” water (i.e. is hydrophobic)
Phospholipids form a bilayer Proteins are embedded in phospholipid
bilayer
Fluid Mosaic Model of the Cell Membrane
Nucleic Acid Deoxyribonucleic acid (DNA) has two
functions: DNA controls protein synthesis in the
cell DNA is replicated and passed on to
progeny cells during reproduction
Cell Cytoplasm Consists of all materials inside the
plasma membrane It is the “bulk” of the cell It is the site of cell metabolism: (1) breaking down complex molecules
for energy and simple “building block” molecules
(2) synthesis of new cell structures
Animal Cell
Ribosome Ribosomes are the sites of protein
synthesis, where an RNA strand is translated into an amino acid sequence.
Protein synthesis is extremely important to cells, and so large numbers of ribosomes are found throughout cells (often numbering in the hundreds or thousands).
Ribosomes
Prokaryotes
Eukaryotes
Prokaryotic Cells Lack a nucleus (though DNA is
concentrated in a region called the cell’s nucleoid)
Lack membranous organelles Are small in size ( < 5 um ) Many have cell walls Belong to the Domain Archaea and
Domain Bacteria
Eukaryotic Cell DNA is housed in a membranous organelle called
the nucleus Membranous organelles exist in the cytoplasm
and perform specific cell functions A network of protein fibers called the
cytoskeleton give the cell shape and stability Cells are large in size (10 – 100 um)
Animal Cell
Plant Cell
Nucleus Control center of the eukaryotic cell Nucleus has three distinct parts: (1) nuclear envelope: double membrane
between nucleoplasm and cytoplasm (2) nuclear pores: openings between
nucleus and cytoplasm (3) nucleoplasm: fluid portion of nucleus
that contains DNA and nucleolus
Nuclear Envelope Nuclear envelope is a double membrane Isolates cytoplasm from nucleoplasm Regulates flow of materials between
cytoplasm and nucleoplasm Outer nuclear membrane is continuous
with cytoplasm’s endoplasmic reticulum
Nucleoplasm Contains the hereditary molecule
deoxyribonucleic acid (DNA) which always remains in the nucleus
Loose “non-condensed” strands of DNA are called chromatin (cell is not dividing)
Tight “condensed” strands of DNA are called chromosomes (cell is dividing)
Nucleolus Present inside of nucleus as a distinct
region Consists of ribosomal RNA, protein,
ribosomes and DNA Nucleoli are the sites of ribosome
synthesis in the cell
Nucleus of a Liver Cell
Endoplasmic Reticulum A complex system of membranes
present within the cytoplasm Endoplasmic reticulum (ER) is
continuous with the nuclear envelope and the plasma membrane
ER functions as an internal transport system for the cell
Endoplasmic Reticulum There are two types of ER: (1) smooth ER: lacks ribosomes on its
surface Involved in lipid synthesis (2) rough ER: outside is studded with
ribosomes Involved in protein synthesis
Endo-membrane System
Golgi Complex A set of specialized membranes derived
from the ER Looks like a stack of flattened sacs or
vesicles Receives contents from ER, modifies
these products, and packages them for transport out of cell
Golgi Complex
Lysosome A membranous sac (or vesicle)
containing digestive enzymes Enzymes used to break down complex
molecules in the cell Lysosomes’ enzymes derived from RER
and lysosome’s sac derived from Golgi complex
Lysosome
Vacuole Membranous sac used for storage of
water, waste, nutrients in the cell Plant cells tend to have one, large
vacuole Animal cells tend to have numerous,
small vacuoles
Plant Cell Vacuole
Peroxisome Similar to lysosome Membrane-bound vesicle that contains
enzymes Enzymes are used to breakdown toxic
substances to hydrogen peroxide Hydrogen peroxide is broken down by
catalase to produce water and oxygen
Mitochondrion Double membrane organelle Outer membrane is smooth Inner membrane is highly folded (in
order to increase inner surface area for cellular respiration)
Folds are called cristae (sing. crista) Inner fluid portion of mitochondrion is
called the matrix
Mitochondrion Structure
Mitochondrion Space between inner and outer
membrane is called the intermembrane compartment
Function of mitochondrion is the breakdown of complex molecules to release energy for the cell (cellular respiration)
All eukaryotic cells have mitochondrion
Muscle Cell Mitochondrion
Chloroplast Present only in plants Site of photosynthesis Double membrane system encloses the
fluid-filled space called the stroma Membrane system within stroma is
organized into interconnected, flattened sacs called thylakoids
Cytoskeleton A network of protein fibers in the cell
cytoplasm Keeps organelles in place in cytoplasm
and allows movement of organelles Provides rigidity and structure to cell Assists in cell reproduction (centrioles)
Cytoskeleton of Nerve Cell
Cytoskeleton Components Actin filaments, a.k.a. microfilaments Microtubules Intermediate Filaments
Actin Filaments Long, extremely thin fibers that occur in
bundles or mesh-like networks Structural role in cytoplasm, just
beneath plasma membrane Interact with protein molecules to allow
movement of cell and its organelles
MicrotubulesLarger than microfilamentsMicrotubule production under the control of an
organizing center called the centrosomeCentrioles, which are composed of
microtubules, are also involved in microtubule assembly
Microtubules involved in maintaining shape of cell and movement of cell and its organelles
Cilia and flagella are produced from microtubules by the centrioles
Centrioles
Cilia: 9 + 2 Arrangment
Flagella and Cilia
Intermediate Filaments Size between microfilaments and
microtubules Provide support to nuclear and plasma
membranes
Evolution of Eukaryotic Cells Endosymbiotic Hypothesis 1) larger “host” prokaryotes formed a
symbiotic relationship with smaller prokaryotes eukaryote and it’s organelles
2) eg. aerobic heterotrophic bacteria mitochondrion
3) eg. cyanobacteria chloroplast