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

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

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.

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

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

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

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

Organelles that store and clean up

Food vacuole in paramecium

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

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

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

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

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

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

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

Endosymbiosis Theory

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