CellsStef Elorriaga

4/4/2016

BIO102

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The domains and kingdoms of life

• Three domains• Bacteria

• Archaea

• Eukarya

• Six kingdoms• Bacteria

• Archaea

• Protista

• Plantae

• Fungi

• Animalia

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What is a cell?

• A cell is the main unit of life

3

How can we study cells?

• Microscopes!

4

Types of microscopes

• Light• Simple

• Compound

• Electron• Scanning electron

microscope (SEM)

• Transmission electron microscope (TEM)

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What is cell theory?

• The cell theory states that cells are the basic units of life

• Proposed by botanist Matthias Schleiden and zoologist Theodor Schwann in 1830

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What is cell theory?

• Three principles comprise the cell theory1. Every living organism is made of one or more cells

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What is cell theory?

• Three principles comprise the cell theory2. The smallest organisms are single cells, and cells are the functional units of multicellular organisms

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What is cell theory?

• Three principles comprise the cell theory3. All cells arise from preexisting cells

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Main two types of cells

• Main two types of cells:• Prokaryotic (meaning “before nucleus”) cells

• Eukaryotic (meaning “true nucleus”) cells

cytoplasmic fluid

cytoplasm

cell wall plasmamembrane

free ribosome

nucleus chromosome(DNA)

ribosomes

cell wall

plasma membrane

cytoplasm

plasmid (DNA)

lysosome

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Prokaryotes

• Unicellular

• All cells identical – no specialized function

• Lack nucleus, other membrane-bound organelles

• Possess specialized surface features and fewer specialized structures within their cytoplasm

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Prokaryotic cells

• Most have a stiff cell wall (peptidoglycan wall)

• Prokaryotic cells can take several shapes• Rod-shaped bacilli

• Spiral-shaped spirilla

• Spherical cocci

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Prokaryotic cells

• Prokaryotic cells have no nuclear membrane or membrane-bound organelles present

• In the central region of the cell is an area called the nucleoid• Within the nucleoid is a single, circular

chromosome of DNA

• Small rings of DNA (plasmids) are located in the cytoplasm

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Prokaryotic cells

• Some bacteria have pili (meaning hairs) • Attachment pili or fimbriae are short and

abundant; they help bacteria adhere to structures

• Sex pili are few in number and long

• Some bacteria have a flagellum• Locomotion

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Eukaryotes

• May be unicellular• Examples: yeast, amoebas

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Eukaryotes

• May be multicellular• Examples: plants, animals

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Eukaryotic Cells

• Differ greatly in appearance and function

• Four basic components in common

1. Plasma membrane• Isolation

• Protection

• Sensitivity

• Support

• Gatekeeper

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Eukaryotic Cells

• Differ greatly in appearance and function

• Four basic components in common

2. Cytoplasm• Material inside the cell but

outside the nucleus

• Contains the cytosol and organelles

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Eukaryotic Cells

• Differ greatly in appearance and function

• Four basic components in common

3. The nucleus• Control center – the “brain of the

cell”

• Contains the DNA

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Eukaryotic Cells

• Differ greatly in appearance and function

• Four basic components in common

4. Organelles• “Organs” of the cell

• Perform specific functions

• Some bound by membranes

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Cytoplasm

• Everything inside the membrane, except the nucleus

• A LOT more on the membrane later

• Includes…• Cytosol = liquid portion

• Organelles

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Organelles

Non-membranous

• Cell wall

• Cytoskeleton

• Cellular extensions

• Microvilli

• Cilia

• Flagella

• Ribosomes

Membranous

• Endomembrane system

• Vacuoles

Double Membrane

• Nucleus

• Mitochondria

• Plastids

• Chloroplasts

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Cell membrane

• All cells are surrounded by a cell membrane

• Also called a plasma membrane

• Consists of a bilayer made of mostly phospholipids

• Critical to cell function

• Discussed in great detail later

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Cell Wall

• Plants, fungi, and bacteria are also have cell walls• Animal cells do not

• All have a cell membrane

Cell membrane

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Cell wall

• Made of polysaccharides secreted through plasma membrane• Non-living

• Exterior to cell

• Cell walls of adjacent plant cells stuck together with pectin

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Cell wall

• Porous• Oxygen, carbon dioxide, water carrying small

molecules flow through freely

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Cell wall

• Adds strength and integrity to cells• Plants, fungi don’t have bones

• Allows them to withstand gravity and wind and grow upright

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Cytoskeleton

• Internal protein network of cells

• Stabilize cell’s 3D shape

• Guide vesicles

Cytoskeleton

intermediatefilaments

Light micrograph showing the cytoskeleton

microtubules

microfilaments

microtubules (red)

microfilaments (blue)

nucleus

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Cytoskeleton

• The cytoskeleton is composed of three types of protein fibers• Thin microfilaments

• Medium-sized intermediate filaments

• Thick microtubules

Cytoskeleton

intermediatefilaments

Light micrograph showing the cytoskeleton

microtubules

microfilaments

microtubules (red)

microfilaments (blue)

nucleus

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Cytoskeleton

• The cytoskeleton regulates the following cell properties:• Cell shape

• Cell movement

• Organelle movement

• Cell division

Cytoskeleton

intermediatefilaments

microtubules

microfilaments

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Cellular extensions

• Cilia and flagella • Hair-like structures that propel cells through fluids

or move fluids past cells

• Arise from a basal body, which anchors them to the plasma membrane

• Basal bodies are derived from centrioles, which are identical in structure to basal bodies

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plasma membrane

section of cilium

ciliumParamecium

protein sidearms

0.1 micrometer

centralpair of microtubules

fusedmicrotubulepair

basal body(extends intocytoplasm)

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Cellular extensions - Cilia

• Example: trachea, Fallopian tubes

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mucus-secreting cells

Cilium power stroke

propulsion of fluid

plasma membranereturn stroke

cilia liningtrachea

Cellular extensions - Flagella

• Substantially longer than cilia• Only example in human body: sperm

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propulsion of fluiddirection of locomotion

continuous propulsionFlagellum

flagellum ofhuman sperm

Cellular extensions - microvilli

• Very small, highly numerous finger-like projections

• Increase absorptive surface area

• Example: small intestine

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Ribosomes

• Site of protein synthesis

• Abundant in cells that produce a lot of protein• Example: human liver cells have on average 13

million ribosomes in each cell!

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Ribosomes

• Made from rRNA (2 units) and proteins

• Polypeptide chain constructed using information provided by mRNA

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Ribosomes

• Many ribosomes can read the same strand of mRNA at once - Polyribosome

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mRNA

• Contains information for:1. Amino acid sequence

2. Final destination of protein

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mRNA

• Final destination of protein bound for cytosol = binds to free ribosome

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mRNA

• Final destination of protein somewhere else = mRNA/ribosome complex associates with endomembrane system

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Endomembrane System

• Elaborate system of membranes used to make and move proteins in a cell

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Organelles Used

• Rough ER

• Vesicles

• Golgi apparatus

• Cell membrane

• Lysosome

Final Destination of Protein

• Outside cell

• Within cell membrane

• Lysosome

Endoplasmic Reticulum

• Collection of membranous tubes and envelopes

• Two forms• Smooth endoplasmic reticulum (sER)

• Site of lipid synthesis, detoxification, calcium storage

• Abundant in liver, kidney, endocrine glands

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Rough Endoplasmic Reticulum

• Gateway to endomembrane system

• Studded with ribosomes

• Proteins made by ribosomes enter rERthrough pore

• Portion of rER pinches off to encapsulate protein in a transport vesicle

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Movement of vesicles

• Vesicles are membranous sacs transporting molecules to the various regions of the membrane system

• Exocytosis1. Vesicles fuse with the plasma membrane2. Export their contents outside the cell

• Endocytosis 1. Plasma membrane extends 2. Surrounds material outside the cell3. Fuses and pinches off to form a vesicle inside the

cell

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Exocytosis

• Some vesicles stay in cytoplasm

• Others migrate to the Golgi apparatus

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Protein-carryingvesicles from the ERmerge with the Golgiapparatus

Vesicles carryingmodified protein leave the Golgi apparatus

Golgiapparatus

Golgi apparatus

• Proteins are modified and/or combined in the Golgi, encapsulated and transported to…

1. Secretory vesicles• Proteins for discharge from cell

• Examples: insulin, antibodies

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Antibody protein is

synthesized on ribosomes

and is transported into

channels of the rough ER

The protein is

packaged into vesicles

and travels to the Golgi

apparatus

Vesicles fuse with the

Golgi apparatus, and

carbohydrates are added

as the protein passes

through the compartments

Completed glycoprotein

antibodies are packaged

into vesicles on the opposite

side of the Golgi apparatus

Vesicles merge with the

plasma membrane and

release antibodies into the

interstitial fluid

Golgi apparatus

forming vesicle

vesicles

(interstitial fluid)

(cytosol)

Golgi apparatus

• Proteins are modified and/or combined in the Golgi, encapsulated and transported to…

2. Cell membrane components• Example: glycoproteins

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Golgi apparatus

• Proteins are modified and/or combined in the Golgi, encapsulated and transported to…

3. Lysosomes• Cytosolically-active vesicles

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Lysosomes

• Contain more than 50 enzymes

• pH of ~4.5

• Break down almost any biomolecule

• Cell’s “garbage disposal”

• Can fuse with other membrane-defined structures and release contents• Fuses with a food vacuole and digests food into

basic nutrients

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Digestiveenzymes aresynthesized onribosomes andtravel throughthe rough ER

The enzymesare packaged into vesicles and travel to the Golgi apparatus

The Golgi apparatus modifiesthe enzymes forexport to thelysosomes

The enzymesare delivered tothe lysosome invesicles

A lysosome fuseswith a food vacuole,and the enzymesdigest the food

Golgi apparatus

digestiveenzymes

lysosome

(interstitial fluid)

(cytosol) foodvacuoles

food

Vacuoles

• Membranous, fluid-filled sacks

• Most cells contain one or more• Animal cells have small ones

• Plant cells typically have one large, central one (may have other, small ones as well)

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Animal Cell Plant Cell

Vacuoles

• Play a role in maintaining cell integrity

• Regulate cell’s water content• Example: Paramecia have contractile vacuoles that

expel water that leaks in through cell membrane

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Vacuoles

• Example: Plant’s central vacuole fills with water to generate turgor pressure

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Vacuoles

• Storage site in plants

• Waste that can’t be excreted

• Poisonous compounds

• Amino acids, sugars

• Pigment (flowers)

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Mitochondria

• Site of ATP synthesis – “powerhouse of cell”

• Double membrane (inner and outer)• Outer membrane is smooth

• Inner membrane has deep folds called cristae

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outermembrane

innermembrane

intermembranespace

matrix

cristae

0.1 micrometer

Mitochondria

• Carry own DNA

• Make some of their own proteins (contain ribosomes)

• Only cellular site to use molecular oxygen

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outermembrane

innermembrane

intermembranespace

matrix

cristae

0.1 micrometer

Mitochondria

• Provide energy = most abundant in cells that need a lot of energy

• Compare: sperm vs cartilage

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Plastids• Contained ONLY by plants and photosynthetic

protists

• Primarily used for storage• Pigments (fruit)

• Starch

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Chloroplasts

• Highly specialized plastid

• Site of photosynthesis

• Contains• Stroma (fluid)• Thylakoids (membranous sacks)

• A stack is called a granum

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Chloroplasts

• Thylakoids contain a pigment called chlorophyll• Gives plants green color

• Captures energy from sunlight

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Nucleus

• Covered with pores

• Water/ions pass through freely

• Ribosomes stud outer membrane

• Continuous with endomembrane system

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• Control center of cell

• Surrounded by nuclear envelope

• Double membrane

Nucleus

• Contains chromatin• Unwound protein-chromosome complexes

• DNA and associated proteins

• Contains all instructions for building cell’s proteins

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Nucleus

• mRNA made in nucleus

• Exits through nuclear pores

• Finds ribosomes

• Translated into protein in the cytoplasm

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Nucleus

• Contains nucleolus

• Site of ribosome synthesis

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Connections between cells

• A tight junction is a watertight seal between two adjacent animal cells

• Plasmodesmata: channels that pass between cell walls of adjacent plant cells

• Gap junctions (animal cells)

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