cell size is limited surface to volume ratio limits upper size larger cells have less surface area...
DESCRIPTION
Cell SizeTRANSCRIPT
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Cell Size is Limited• Surface to Volume Ratio limits upper size• Larger cells have less surface area relative to volume
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Cell Size
Size ranges of cells: Cell Type Diameter Arechaea 0.1 - 1.0 μm Most bacteria 1.0 - 10.0 μm Most eukaryotic cells 10.0 - 100.0 μm
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Cell Size
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Tour of the Eukaryotic Cell
All organisms are made of cellsThe cell, as a microcosm, illustrates the following principles:
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Cells as microcosms
1. Life arises from interactions among cellular components
2. Ordered cellular processes are based upon ordered structures
Examples of cell processes:protein synthesis, respiration, photosynthesis, cell-cell recognition, cellular movement, membrane production and secretion
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3. Cells are excitable, responding to environmental stimuli, and exchange materials and energy with their environment.
4. Evolutionary adaptations are the basis for the correlation between structure and function.
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Cell size is limited by metabolic requirements
• The lower limits are probably determined by the smallest size with enough:– DNA to program metabolism– cellular components to sustain life and reproduce
• The upper limits of size are imposed by the surface area to volume ratio. – As a cell increases in size, its volume grows
proportionately more than its surface area.
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SA/Volume
The surface area of the plasma membrane must be large enough for the cell volume, in order to provide an adequate exchange surface for oxygen, nutrients and wastes.
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Why cells have organelles
• Internal membranes compartmentalize the functions of a eukaryotic cell
• Most eukaryotic cells have 1000 X the volume of the average Eubacteria/Archaea cell, but only 100 X the surface area.
• i.e. – eukaryotic cells have a smaller surface area to volume ratio
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How Eukaryotic cells compensate for a small SA/Volume ratio
• Eukaryotic cells compensate by having internal membranes which:– Give the cell compartments where
reactions occur without interference from other parts of the cell.
– Allows for specialized functions – cells become specialized – skin cells, nerve cells etc
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Eukaryotic Organelles
• Nucleus• Mitochondria• Endoplasmic Reticulum (ER)• Vacuoles• Golgi Bodies (Apparatus)• Chloroplasts• Centrioles
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The Nucleus
The nucleus is a large membrane-bound organelle, in all eukaryotic cell
It contains most of the genes that control the entire cell - the genetic library
It is enclosed by a nuclear envelope
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Nuclear envelope• A double membrane• Two lipid bilayers separated ~20 to 40 nm.• Each bilayer has it’s own specific proteins.• Attached to the inner membrane is a network
of protein filaments, the nuclear lamina, which stabilizes nuclear shape.
• Is perforated by pores that regulate movement of molecules into and out of the nucleus
• The envelope's inner and outer membranes are fused at the lip of each pore.
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DNA
• DNA is organized with proteins into a complex called chromatin.– Chromatin - Complex of DNA and proteins, which
makes up chromosomes• Chromosomes - Long thread-like structures
nucleotides that make up our genes
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Nucleolus
• The most visible structure within the non-dividing nucleus
• Makes Ribosomes• Consists of of nucleolar organizers (= genes for
ribosomal RNA synthesis) (thus the nucleolus contains DNA)
• Packages of ribosomal subunits• Ribosomal subunits pass through nuclear pores to the
cytoplasm, where their assembly is completed.
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Ribosomes
• A cytoplasmic organelle that make proteins• Are complexes of RNA and protein• Two types
1. free floating2. bound
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Free Floating and Bound Ribosomes
• Are structurally identical and interchangeable.• Free floating ribosomes are suspended in the
cytosol– Make proteins for use inside the cell
• Bound ribosomes are attached to the outside of the endoplasmic reticulum.– Make proteins for use in membranes and export
out of cell
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Ribosomes – are not membrane bound
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Task 1
• Draw a model of a nucleus. Include the following details:
• Lipid bilayer – inner and outer layer and inter-membrane space
• Nuclear pores• Nuclear lamina• Chromatin• Nucleolus• Nucleoplasm
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Task 2Complete the size comparison chart (handout)