Cell Structure and Function

CHAPTER 7

RECOGNIZE ANYTHING?

GETTING TO KNOW YOUR CELLS…

= we will see in lab!

PLANT AND ANIMAL CELLS

onion cell slide

Elodea cell slide

human cheek cell slide

*If your slides look nothing like these, you need to let me know!

7-1 LIFE IS CELLULAR

• What is a cell?

• The smallest unit of living things

• One of the 8 characteristics of living things

• If they are so small, how did we ever find them?

• The invention of the microscope!

THE DISCOVERY OF THE CELL

• “out of sight, out of mind”

• 2 inventors of the microscope

• Robert Hooke

• Looked at cork (plant) cells

• First to use the term “cell”

• Anton van Leeuwenhoek

• We know him!

• Saw organisms in pond water

CELL THEORY

• What is a theory?

• Schleiden- claimed all plants made of cells

• Schwann- claimed all animals made of cells

• Virchow- claimed new cells only come from existing cells

• The Cell Theory states:

• 1. all living things are composed of cells

• 2. cells are the basic unit of structure and function in living things

• 3. new cells are produced from existing cells

EXPLORING THE CELL

• The advancement of microscopes

• New technologies:

• Fluorescent labels- track certain parts

• 3D- structural detail

• HD videos- show movement

• Light microscopes still a challenge- why?

• Light rays can be diffracted

• So, what else can we use?

ELECTRON MICROSCOPY

• Beams of electrons- show more detail

• What are the 2 types?

• Transmission EM

• Shows internal structures

• Specimen must be very thin

• Scanning EM

• Shows 3D surface images

• Must be in a vacuum- preserved and dehydrated

SCANNING PROBE MICROSCOPES

• 1990s

• View the surface with very fine probes

• No need for a vacuum

• Can view single atoms

WIDE VARIETY OF CELLS

• Cells come in all sizes- from 0.2nm to amoeba

• 2 characteristics of ALL cells:

• 1. Surrounded by a barrier (membrane)

• 2. Contain DNA (at some point)

• So if all cells have these, then how do we classify them…?

• By the presence/absence of a nucleus!

PROKARYOTES & EUKARYOTESProkaryotes Eukaryotes

No nucleus Has a nucleus

Smaller, simple Larger, complex

Still has genetic material Genetic material in nucleus

Follows 8 characteristics Follows 8 characteristics

Internal structures/membranes

Specialized

Can be single or multi-celled

Ex: bacteria Ex: humans

7-2 EUKARYOTIC CELL STRUCTURE

• Eukaryotic cells = very complex

• Drive processes of all living things

• Remember the 8 characteristics?

• Contain many common organelles

• “Little organs”

THE CELL AS A “FACTORY”

• Each organelle has a specific function/role

• 2 main parts:

• Cytoplasm- part of the cell outside the nucleus

• Nucleus- control center

• “the boss”

THE NUCLEUS

• Job: control center of the cell

• Contains all DNA

• Instructions for proteins, etc. to be made by cell

• Structure:

• Double membrane

• Nuclear pores- allows material in/out

• Chromatin- DNA + protein

• Condenses to form chromosomes

• Nucleolus- where ribosome production begins

RIBOSOMES

• Job: make proteins!

• Gets all “orders” from the nucleus

• Consists of RNA and protein

• Free or bound

ENDOPLASMIC RETICULUM (ER)

• Job: conveyor belt for protein synthesis

• For proteins going out of the cells

• Rough ER: ribosomes attached

• Smooth ER: no ribosomes

• Enzymes here

• Produce membrane lipids

• Detox drugs (liver)

GOLGI APPARATUS

• Job: modify, sort and package proteins

• Sent to be stored or secreted

• Like a UPS store- final touches and ship!

LYSOSOMES

• Job: digestion of carbs, proteins and lipids for cell use

• Enzyme filled “clean-up crew”

• Get rid of “junk”

• Old organelles

VACUOLES

• Job: storage

• Water, salt, proteins, carbs, etc.

• Plants- large vacuoles- pressure gives support

• Animals- maintain water balance

• Maintaining a balance? What’s that called?

• Homeostasis!

• Ex: paramecium- contractile vacuole

SUPPLYING THE CELL WITH ENERGY!

• metabolism at the cell level

• Living things get their energy from…

• Food (animals)

• The sun (plants)

MITOCHONDRIA

• Job: powerhouse of the cell

• Chemical energy from food -> compounds the cell can use

• Double membrane (inner is folded up)

• Inherited from mother

CHLOROPLASTS

• Job: “solar powered” plants (photosynthesis)

• Energy from sun -> energy the cell can use

• Double membrane (internal folds up- chlorophyll)

ORGANELLE DNA

• Mitochondria and chloroplasts have their own DNA

• Lynn Margulis- endosymbiotic theory

• Mitochondria and chloroplasts are descendants of prokaryotes

• Symbiotic relationship with eukaryotic cell

CYTOSKELETON

• Job: structure and transport

• Protein filaments- maintain shape

• Microfilaments

• Threadlike actin- tough/flexible

• Microtubules

• Hollow tubulin- cell shape and division

• Mitotic spindle

• Centrioles

• Cell projections (cilia and flagella)- movement

7-3 CELL BOUNDARIES

• 1 of the 2 characteristics all cells have

• What is the other one?

• Separates the cell from the rest of its environment

• Cell membrane: regulates what goes in/out

• Cell wall: strong supporting layer

CELL MEMBRANE

• Thin, strong

• Job: regulates what goes in/out

• Protection/support

• Lipid bilayer

• “fluid mosaic”

• Proteins within

• Carb chain for identification

• Protein channels

CELL WALL

• Found in plants, bacteria, prokaryotes, etc.

• NOT in animals

• Outermost layer- outside membrane

• Job: support/protection

• cellulose

MOVEMENT ACROSS MEMBRANES

• Membranes regulate movement of liquid + dissolved molecules from one side to another

• Permeable= when a membrane allows a substance to cross it

• Impermeable= when a membrane does not allow a substance

• Cell membranes are selectively permeable

• Let some things in and not others

CONCENTRATION

• Particles in a solution are always moving

• Concentration: how much solute there is in a solution

DIFFUSION

• Movement of particles from high concentration to low concentration

• When equal on both sides: equilibrium is reached

• Based on random particle movement- no energy needed!

• Even at equilibrium, particles still move

• Going in = going out

OSMOSIS

• Diffusion of water through a selectively permeable membrane

• isotonic solution: at equilibrium

• hypertonic: greater concentration of solute

• hypotonic: less concentration of solute

OSMOTIC PRESSURE

• Pressure on the hypertonic end of a selectively permeable membrane

• hypertonic solution- water out (cell shrinks)

• hypotonic solution- water in (cell expands)

• isotonic solution- stays same

• bodily fluids are isotonic!

• Cell walls prevent shrink/expanding

FACILITATED DIFFUSION

• some molecules travel easily thru membrane

• Use protein channels

• Protein “facilitates” (helps) diffusion

• Still moving from hi to lo concentration- no energy needed!

ACTIVE TRANSPORT

• For SMALL molecules…

• Movement against concentration gradient

• Requires energy (lots)!

• Use protein “pump”

• Changes shape and pumps molecules across

ACTIVE TRANSPORT

• For LARGE molecules…

• Movements of the cell membrane

• Folds/extensions of membrane

• Break off to form vacuole around molecule

• Endocytosis- bring molecules IN the cell

• Exocytosis – get molecules OUT of the cell

2 TYPES OF ENDOCYTOSIS

• 1. phagocytosis: “cell eating”

• Membrane and cytoplasm extend and engulf particle

• 2. pinocytosis: take up liquid in tiny pockets of membrane

Both processes move things INTO the cell!

EXOCYTOSIS

Movement of things OUT of the cell!

7-4 THE DIVERSITY OF CELLULAR LIFE

• Cells have many similarities

• What are some?

• They can also be very different

• Specialization!

UNICELLULAR ORGANISMS

• Carry out all the processes of a living thing

• Only one cell

MULTICELLULAR ORGANISMS

• Depend on communication and cooperation among cells

CELL SPECIALIZATION

• Cell specialization: cells develop in different ways to perform different tasks (structure -> function!)

• Specialized animal cells

• RBC- O2 binding proteins

• Muscle cells- overdeveloped cytoskeleton

• Specialized plant cells

• Guard cells- open/close stomata

LEVELS OF ORGANIZATION

• Cells

• Tissues: group of similar cells with specific functions

• Organs: different tissues working together

• Organ systems: group of organs working towards a certain function