Transcript 1285174151_463953

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Chapter 3
Cell Structure
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Introduction
• The cell is the basic unit of biological
organization
• Basic composition
– Protoplasm
– Cell membrane
– Organelles
• Eukaryotic vs. prokaryotic
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History of the Cell Theory
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History of the Cell Theory
• Proposed in 1830s by Schleiden and
Schwann
• Modern cell theory
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Cells are the smallest complete living things
All organisms are composed of one or more cells
Cells arise only from other cells
All existing cells are descendants of the first cells
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Anatomy of a Typical
Eukaryotic Cell
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The Cell Membrane
• Double phospholipid layer with embedded
proteins
• Membrane transport: selectively
permeable membrane
– Osmosis
– Protein channels
– Active transport
– Fluid mosaic model
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The Cell Membrane
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Cytoplasm of the Cell
• Mostly water with chemical compounds in
solution or colloid
– Solution vs. colloid
• Individual vs. clumped atoms or ions distributed in
medium
• Polar compounds go into solution
• Nonpolar compounds go into colloidal
suspension
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The Nucleus
• Control center of the cell
• Nuclear membrane has pores to allow the
passage of substances
• Chromatin genetic material inside
nucleoplasm
• Nucleolus: site of ribosome formation
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The Mitochondria
• Powerhouses of the cell
• Cristae: inner folds where cellular
respiration occurs
• Energy requirements of cell determine
cristae number
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Lysosomes
• Digestive enzyme packages
• Function
– Digest stored food
– Maintenance and repair of organelles
– Suicide agents for old or weak cells
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Endoplasmic Reticulum
• System of membranes that makes up
channels
• Connects with outer nuclear and cell
membranes
• Cisternae: sac like or channel like cavities
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Endoplasmic Reticulum (cont’d.)
• Rough ER
– For protein synthesis
– Attached ribosomes
• Smooth ER
– Fat transport
– Sex hormone synthesis
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Endoplasmic Reticulum (cont’d.)
• Golgi apparatus
– Collection of flat saclike cisternae
– Concentration and collection of cellular
compounds
– Storage warehouses of the cell
– Carbohydrate synthesis site
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Ribosomes
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Distributed throughout cytoplasm
Attached to rough endoplasmic reticulum
No membrane covering
Site of protein synthesis
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Ribosomes (cont’d.)
• Protein functions
– Structure, enzymes or catalysts, immune
response
• DNA contains the code for a particular
protein
– DNA found in nucleus
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Ribosomes (cont’d.)
• Transcription
– Messenger RNA copies DNA code and leaves
nucleus
• Translation
– Transfer RNA picks up amino acids
– Ribosomes link amino acids together
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Ribosomes (cont’d.)
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Centrioles
• Centrosome: two centrioles at right angles
to each other
– Composed of nine sets of triplet fibers
• Form spindle fibers during cell division
• Guide duplicated chromosomes to
daughter cells
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Cilia and Flagella
• Hairlike protrusions from cell membrane
• Nine double fibrils around two single
central fibrils
• Cilia move materials across cell surface
• Flagellum propels cell through a medium
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Plastids of Plant Cells
• Chloroplasts
– Most common plastid
– Photosynthesis: conversion of light into
chemical energy
– Granum
• Made of thylakoids
• Connected by lamella
• Chromoplasts: carotenoid pigments
• Leucoplasts: store food
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Plastids of Plant Cells (cont’d.)
• Cell membrane surrounded by cell wall
• Cell wall composed of cellulose
– Cellulose
• Dietary fiber
• Synthesized by Golgi bodies
• Animal cells do not have cell walls
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Summary
• Discussed the modern cell theory and its
origins
• Discussed the different parts of eukaryotic
cells including the cell membrane,
cytoplasm, and organelles
• Discussed protein synthesis
• Described some of the differences
between plant and animal cells
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