cp bio: chapter 7 cell structure and function the cell is the basic unit of life 1
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CP BIO: Chapter 7 Cell Structure and Function
The cell is the basic unit of life
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Discovery of the Cell• Robert Hooke 1660s
– cork “cells”
• Anton von Leeuwenhoek 1660s– first high-mag microscope– living cells, bacteria– Pond water, blood, saliva
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All living things made of cells
• Matthias Schleiden 1830s– all plants made of cells
• Theodore Schwann 1830s – all animals made of cells
• Rudolf Virchow 1850s– new cells come from cell division
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The Cell Theory
1. All organisms are made of one or more cells2. The cell is the basic unit of life. Cells that
form part of a larger organism still do their own life processes.
3. All cells come from pre-existing cells
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Why are all cells small?
Cells vary in size and shape
• Must contain raw materials and molecules needed by cell
• Must have fast exchange with environmentSurface area must be large compared to volume
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size increases (1mm2mm) 2X (14) 4X
area increases (24/6) 4X (96/6) 16X
volume increases (8/1) 8X (64/1) 64X
Cells have large Surface-to-Volume Ratio
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Two basic kinds of cells Prokaryotic Eukaryoticsmall and simple larger and more
complexno nucleus nucleusbacteria all other organisms
Both have: DNA & complex chemicals, cell membrane, cytoplasm, ribosomes
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Two kinds of cells
Bacteria (purple) in animal cell (pink)
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Prokaryotes “before nucleus”
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All prokaryotes have1. Nucleoid
• Region containing DNA, one chromosome2. Cell (plasma) membrane
• Encloses cytoplasm• Controls what enters and leaves cell
3. Cell wall• Outside membrane• Cell shape and protection
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SOME prokaryotes have
4. Capsule – protective layer • Slimy or sticky coating, outside cell wall
5. Pili – extensions of cytoplasm• to attach to other cells, pass signals
6. Prokaryotic flagella – for movement7. Plasmids – small rings of DNA
• have special genes
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Some prokaryotic cells
Common shapes of bacteria
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Eukaryotic Cells “true nucleus”
Eukaryotes have membrane compartments– Larger than prokaryotes (10-100 m)– Many organelles – tiny “organs”, with specific
functions– Most organelles are enclosed by a membrane
• Keeps chemistry inside organelle separate from rest of cell
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7.2 Cell StructureThe cell is like a city – every part has a job to do. Together these parts keep the cell alive.
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Cytoplasm
• Watery solution outside nucleus
• Has many dissolved substances for metabolism
• Site for chemical reactions• Contains organelles, each
has a function
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Nucleus- control center of cell
• Has most of the DNA • Chromosomes – structures
containing DNA• Chromatin – loose, thread-
like form of chromosomes when cell is not dividing
• Nucleolus – makes ribosomes
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Nuclear Envelope
• Membrane surrounding nucleus• Many pores for molecules to pass through• Selectively permeable – controls what moves
in and out of nucleus
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Organelles that Build Proteins
Ribosomes• Makes proteins, uses instructions in DNA• Made of RNA and protein• Made in nucleolus, move to cytoplasm and
rough ER
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Endoplasmic Reticulum- membrane channels throughout cell- make and transport materials- large surface area for reactions
Rough ER - has ribosomes - makes and modifies proteins
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Smooth ER• No ribosomes on membrane • Makes and transports lipids• Other functions in special tissues
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Golgi Apparatus
• Layers of membrane sacs• Receives proteins made in ER• Sorts and packages proteins
into tiny vesicles• Final products may be used by
cell (ex. lysosome) or exported from cell
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LysosomesMembrane sacs of digestive enzymes1. Break down wastes and worn-out cell parts2. Recycle molecules the cell can use3. In one-celled, join to food vacuoles to digest food 4. In development, remove tissue no longer needed (ex. tadpole tail)5. In defense, white blood cells digest bacteria6. In Cell death – when cell is damaged beyond repair
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Organelles that capture and release energy
Mitochondria“Powerhouse of the cell” – site for cell respiration• Releases chemical energy from food and
changes into energy cell can use ATP• ATP – energy molecule in all organisms
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Plastids – in plants Chloroplasts• Site for photosynthesis: capture sun energy and
change it into chemical energy of food• Layered membranes inside contain green pigment
chlorophyll
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Leukoplasts and Chromoplasts
Leukoplasts store starch
Chromoplasts store other pigments -flowers, fruits, seeds
24In red pepper
In potato
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Mitochondria and Chloroplasts are different from other organelles
1. double-layered membrane organelles - inner membrane deeply folded/layered - large surface area for fast chemical processes
2. have their own DNA and ribosomes- can self-replicate as needed
- make their own enzymes for reactions
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Organelles that store and clean up
Food vacuole in paramecium
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Plant Vacuoles
Stores water and substances needed for photosynthesis
Also has enzymes to recycle molecules
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Contractile Vacuole
• In some one-celled organisms that live in fresh water
• Water enters cell from environment
• Vacuole pumps out excess water
• Keeps homeostasis
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Lysosomes are stained in this slide
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The Cytoskeleton
• Protein framework inside cell• Attach to cell membrane to
keep cell shape• Anchor organelles• Transport materials inside
cellTwo kinds: microfilaments and microtubules
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Microfilaments
• Flexible, elastic threads• Support cell and help cells move
– Move substances around inside cell– Cytoplasmic streaming– May form pseudopods
Cytoplasmic streaming lets
amoeba eat by encircling food 32
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Microtubules
• Hollow rigid tubes keep cell shape• Tracks for moving molecules in cell• Also found in cilia, flagella (for movement) and in
centrioles and spindle fibers (for cell division)
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Cytoskeleton and Cell Wall
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Cilia and FlagellaExtensions on cell surface
• Cilia – short, many, like “oars”– Ex. line air passages in our body
- cover Paramecium
• Flagella – longer, one or a few, move like a “whip”– Ex. Human sperm, euglena
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Centrioles and Spindle Fibers
• Help in cell division• Centrioles (only in animal cells)
– Organize spindle fibers• Spindle fibers (in all eukaryotic cells)
• Organize and separate chromosomes when cell divides
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Cell BoundariesKeep cell contents separated from surroundings
Cell (plasma) membrane – in ALL CELLS• Selectively permeable• controls which substances move in or out of
cell• Maintains homeostasis
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The Cell Membrane
Double layer of phospholipids and proteins
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The Cell Wall• In many organisms, but NOT animals• Outside cell membrane• For shape, support, protection• Some substances can pass through• In plants – mostly cellulose• Also in fungi, most bacteria, some protists
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Cellulose fibers in cell wall
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Cell Junctions• Connects cells to form tissues• Cells can communicate and share materials
Gap junction anchoring junction tight junction
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How do plant and animal cells differ? Plant cells also have:
1. rigid cell wall, contains cellulose 2. chloroplasts – do photosynthesis
3. large central vacuole – stores water and molecules for photosynthesis
Animal cells have: 1. centrioles – for cell division
2. lysosomes – break down wastes3. some have flagella or cilia
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Endosymbiosis TheoryTheory for how eukaryotic cell evolved
1. Prokaryotes are different sizes2. Larger prokaryotes ate smaller ones3. Some were not digested, but became part of cell4. Might have survival advantage
– ex. make its own food; use energy efficiently
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Endosymbiosis Theory
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Evidence to support theory
Chloroplasts and mitochondriaa) have double membranesb) Have their own DNA and ribosomesc) Can self-replicate
May have once been separate organisms