Transcript Understanding Our Environment

Cell Structure
Chapter 5
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Cell Theory
Schleidon and Schwann
• All organisms are composed of one or more
cells.
 Metabolism and heredity occur within
these cells.
• Cells are the basic units of organization for
all organisms.
• Cells arise only by division of a previously
existing cell.
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Three Main Features of ALL Cells
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1. Surrounded by a plasma membrane that
encloses the cell and separates its contents
from its surroundings
- phospholipid bilayer with embedded
proteins (transport proteins and receptor
proteins)
2. Genetic material is enclosed within a
nucleus or a nucleoid
3. Cytoplasm
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Cells Are Small
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The human body has approx. 100 Trillion
Cells
Cell diameter range: 7.5 micrometers (RBC)
to 150 micrometers (ovum)
Cells Are Small
•
Advantage of small cell size is explained by
surface area-to-volume ratio.
 As a cell’s size increases, its volume
increases much more rapidly than surface
area.
 Cell membrane plays a key role in
controlling cell function.
- Small cells have more surface area per
unit volume thus more effective
communication.
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•
Prokaryotic Cells
Bacterial cells are small, consisting of
cytoplasm surrounded by a plasma
membrane enclosed within a rigid cell wall of
peptidoglycan (carbohydrate matrix
crosslinked by short polypeptide units)
 Categorized by cell wall structure:
- Gram Positive - Thick, single-layered cell
wall. Gram Negative - Multilayered cell
wall (less peptidoglycan)
 Many propelled by flagellum (flagella).
 Lack internal organization.
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Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies
Eukaryotic Cells
•
Interior of eukaryotic cells contain numerous
membrane-bound structures (organelles)
that close off compartments to allow multiple
simultaneous biochemical processes.
 Vesicles - Storage and Transport (Plants
and Animals)
 Nucleus – Chromosomes (DNA)
 Cytoskeleton - Internal Structure
 Central Vacuole - Storage (Plants Only)
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Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies
Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies
Nucleus
Largest organelle: repository of genetic info.
DNA is divided into chromosomes found in
nucleus (chromatin)
• Nucleolus in center: synthesizes rRNA
• Nuclear envelope made of two phospholipid
bilayers
• Nuclear pores in envelope filled with proteins
allow passage of two types of molecules
•
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Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies
Endoplasmic Reticulum
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Internal membrane composed of
phospholipid bilayer and embedded proteins.
 Weaves through cell, creating series of
cisternal channels between its folds
(cisternae)
Rough ER - Surface regions covered with
ribosomes.
 Synthesizes proteins for export.
Smooth ER - Membrane has few embedded
ribosomes, and is embedded with enzymes
for lipid synthesis, carbohydrate synthesis
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Golgi Apparatus
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Collection of interconnected flattened stacks
of membranes (Golgi bodies).
Each membrane is called a cisternae.
 Function in collection, packaging, and
distribution of molecules synthesized in
one place, and utilized in another place
within the cell.
- Cis face - Receiving end
- Trans face - Discharging end
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Vesicles
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Lysosomes - Membrane-bound digestive vesicles
that arise from Golgi apparatus.
 Contain degrading enzymes.
- Break down old organelles and other
structures and recycles them
Microbodies - Bear enzymes for metabolism
 Glyoxysome - Convert fat into carbohydrates
 Peroxisome – Detoxify (those of kidneys and
liver contain degrading enzyme catalase to
detoxify hydrogen peroxide) metabolic waste,
drugs, etc.
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Ribosomes
•
Ribosomes are site of protein synthesis.
 Made up of rRNA bound within complex of
several dozen different proteins.
 Composed of two subunits (large RNA and
smaller ribosomal protein)
- Join to form functional ribosome only
when they attach to messenger RNA.
 Assembled in nucleolus within the nucleus.
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Organelles With DNA
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Mitochondria
 Bound by smooth outer membrane and an
inner membrane folded into cristae.
 Contain own DNA.
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Organelles With DNA
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Chloroplasts
 Contain photosynthetic pigment chlorophyll
that gives most plants their green color.
 Double membrane
 Grana - Stacked membranes internal to
inner membrane.
- Contain disk-shaped Thylakoids which
also contain light-capturing pigments on
surface
Stroma – fluid surrounding grana
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Chloroplast Structure
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Organelles With DNA
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Centrioles - Barrel-shaped organelles usually
located near nuclear membrane.
 Help assemble microtubules.
 Some appear to contain DNA.
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Cytoskeleton
•
Network of protein fibers supports cell shape.
 Individual fibers formed by polymerization.
- Actin Filaments – cell movement and
formation of cellular extensions
- Microtubules – cell movement and
moving material within cell
- Intermediate Filaments – line organs and
body cavities
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Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies
Cell Movement
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Some cells crawl via a pseudopod.
Moving Material Within the Cell
 Short Distances – ER and Golgi Apparatus
 Long Distances - Molecular Motors
- Vesicle
- Microtubule
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Cell Movement
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Many eukaryotic cells contain flagellum
consisting of a circle of nine microtubule
pairs surrounding two central microtubules:
“9+2 Structure” Flagella undulates with the
help of flagella motor protein dynein.
Cilia: short cellular projections often
organized in rows that carry out a multitude
of functions
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Plant Cells
Central Vacuole - Functions as storage
center and helps increase surface-to-volume
ratio by stretching (swelling) cell
• Cell Walls
• Chloroplasts
Plastids: organelle for photosynthesis and
starch storage
-Choroplasts
-Leucoplasts
-Amyloplasts
•
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Endosymbiosis
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Theory of endosymbiosis proposes some
eukaryotic organelles evolved by symbiosis.
 One species of prokaryote was engulfed
and lived inside another.
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