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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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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path of light rays (bottom to top) to eye
Ocular lens enlarges primary image formed by
objective lenses
Objective lenses (those closest to specimen) form
the primary image. Most compound
light microscopes have several
stage (holds microscope slide in position)
Condenser lenses focus light rays through specimen
illuminator
microscope base housing source of illumination
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accelerated electron flow (top to bottom)
condenser lens to focus beam of electrons onto
specimen
specimen
objective lens
intermediate lens
projector lens
viewing screen (or photographic film)
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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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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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cytoplasm
nucleus
plasma membrane
nuclear envelope
nucleoplasm
chromatin (DNA proteins)
nucleus
Fig. 4.11, p. 62
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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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assorted vesicles
Golgi body
smooth ER
rough ER
DNA instructions for building polypeptide chains
leave the nucleus and enter the cytoplasm.
The chains (green) are assembled on ribosomes in
the cytoplasm.
Fig. 4.13, p. 64
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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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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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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