Cell Structure and Function

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Cell Structure and Function

• Starr/Taggarts
• Biology
• The Unity and Diversity of Life, 9e
• Chapter 4

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Fig. 4.1, p. 52
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Key Concepts

• All organisms are composed of cells
• The cell is the basic unit of life
• All cells have a double-layered plasma membrane
• Membranes consist largely of phospholipid and
  protein molecules

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Key Concepts

• Organelles are membrane-bound compartments inside
  eukaryotic cells
• Prokaryotic cells do not have organelles
• When cells grow, they increase faster in volume
  than in surface area
• Different microscopes modify light rays or
  accelerated beams of electrons that allow small
  images to be observed

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Basic Aspects of Cell Structure and Function

• Plasma membrane
• Lipid bilayer
• Proteins
• Channels, transport, pumps, receptors
• DNA-containing region
• Cytoplasm

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Cell Size and Shape

• Surface to Volume Ratio
• Volume increases more rapidly than surface area
• Restrictions on
  size and shape

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cluster of four cells
wing
wing
Fig. 4.2, p. 54
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Microscopes

• A - Light microscope
• B - Transmission Electron Microscope
• C - Scanning Electron Microscope

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Trypanosoma (protozoan) 25 µm long
Chlamydomonas (green alga) 5-6 µm long
Poliovirus 30 nm
mitochondrion 1-5 µm
HIV (AIDS virus) 100 nm
chloroplast 2-10 µm
frog egg 3 mm
T4 bacteriophage 225 nm long
human red blood cell 7-8 µm diameter
Typical plant cell 10-100 µm
DNA molecule 2 nm diameter
Escherichia coli (bacterium) 1-5 µm long
tobacco mosaic virus 300 nm long
UNAIDED HUMAN EYE
LIGHT MICROSCOPE (DOWN TO 200 NM)
ELECRON MICROSCOPES (DOWN TO 0.5 NM)
1mm
100 µm
10 µm
1 µm
100 nm
10 nm
1 nm
0.5 nm
Fig. 4.6, p. 57
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Defining Structures of Eukaryotic Cells
A Plant Cell
An Animal Cell
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Major Cellular Components

• Nucleus
• Ribosomes
• Endoplasmic reticulum
• Smooth and Rough
• Golgi body
• Various vesicles
• Mitochondria
• Cytoskeleton

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Components of the Nucleus

• Nuclear envelope - Surrounds nucleus
• Nucleoplasm - Fluid interior portion
• Chromosome - One DNA molecule and associated
  proteins
• Chromatin - Total collection of all DNA molecules
  and associated proteins
• Nucleolus - RNA and proteins that will be
  assembled into ribosomal subunits

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The Nuclear Envelope

• Double - membrane system
• Two lipid bilayers
• Surrounds nucleoplasm
• Pores allow exchange

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The Cytomembrane System

• Organelles in which lipids are assembled and
  proteins are produced and modified
• Endoplasmic reticulum
• Golgi bodies
• Vesicles

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The Endoplasmic Reticulum

• Rough and Smooth
• Presence or absence of ribosomes
• Rough Proteins
• Smooth Lipids

Rough ER
Smooth ER
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Golgi Bodies

• Enzymatic finishes on proteins and lipids, and
  packaging in vesicles
• Vesicles
• Lysosomes
• Peroxisomes
• Transport

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Mitochondria

• Production of ATP
• Double-membrane system
• Two distinct compartments
• Have their own DNA
• Divide on their own
• Have ribosomes

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Chloroplast

• Found in photosynthetic eukaryotes
• Two outer membranes
• Semifluid stroma
• Inner thylakoid membrane system
• Photosynthetic pigments

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Components of the Cytoskeleton

• Microtubules
• Tubulin subunits
• Cell division and movement
• Microfilaments
• Actin subunits
• Movement and shape

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Components of the Cytoskeleton

• Intermediate Filaments
• Only in animal cells of specific tissues
• Mechanically strengthen cells or cell parts and
  help maintain shape
• Six known groups

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Structural Basis of Cell Motility

• Three Mechanisms
• Length of microtubule can change
• Parallel microtubules slide in opposite
  directions
• Shunting of organelles

Sliding mechanism for beating of flagella
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Cell Surface Specializations

• Eukaryotic Cell Walls

A single-celled protist
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Plant Cell Wall

• Cell secretions form lamella
• Plasmodesmata (channels)
• Primary and Secondary walls

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Plant Cell Walls

• Deposition of layers inside primary wall
• Stiffen wall
• Maintain shape

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Cell-to Cell Junctions

• Plants
• Plasmodesmata
• Animals
• Tight Junctions
• Adhering Junctions
• Gap Junctions

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Prokaryotic Cells The Bacteria

• No nucleus - DNA in free cytoplasm
• Smallest of all cells
• Most have a cell wall
• Polysaccharides cover cell wall of many species
• No membrane-bound organelles
• Flagella lack 92 array of microtubules

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Bacterial Cell
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In Conclusion

• The cell theory states
• All living cells are composed of cells
• The cell is the smallest unit of life
• New cells arise only from pre-existing cells
• Cells have a plasma membrane, cytoplasm, and a
  region of DNA
• The plasma membrane maintains the cell as a
  separate entity

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In Conclusion

• The cytoplasm is all the fluids, ribosomes and
  organelles in eukaryotic cells between the
  nucleus and plasma membrane
• Membranes consist of a bilayer of lipids and
  proteins embedded in the bilayer or attached to
  the surface.
• Proteins carry out most of cell membrane functions

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In Conclusion

• Membranes divide functional compartments into
  organelles
• Prokaryotes do not have organelles
• Organelle membranes separate metabolic reactions
• developed by M. Roig