Cells

Chapters 7, 8, 11, and 12

A Tour of the Cell

Chapter 7

Cell Theory

1. All organisms are made up of cells.

2. New cells come only from old cells.

3. The cell is the basic unit of life.

Prokaryotic vs. Eukaryotic Cells

• What is the major difference between the two?

• Prokaryotes – “Before Nucleus”

• Contain no membrane bound organelles

• Limited to Nucleoid region, Ribosomes, Plasma membrane, and cell wall

• Eukaryotes – “True Nucleus”

• Contains membrane bound organelles

Cellular Questions to Ponder?

• Why are most cells microscopic?• Do larger organisms have larger cells than

smaller ones?• Cells need a large surface area to volume

ratio (in the ballpark of 6:1).• Allows for cell to aquire more nutrients and

expel more waste• Why do cells have folded membranes?• Folded membranes allows for even more

surface area.

Internal Membranes

• Internal membranes compartmentalize the functions of a eukaryotic cell:

• Partition cell into compartments

• Enzymes built into membranes because compartments can provide separate environments

OrganellesWhat do you know about the organelles below?

• Nucleus• Endoplasmic Reticulum• Golgi Body (apparatus or complex)• Lysosomes• Mitochondria• Chloroplasts• Microtubules, Intermediate filaments, and microfilaments• Flagella and cilia• Centrioles• Cell Walls• Vacuoles• Peroxisomes

Nucleus contains Genetic Library

• Contains DNA in form of chromosomes

• Surrounded by nuclear envelope

• Contains Nucleolus – portion of DNA that manufactures components of ribosomes which are then shipped to cytoplasm to assemble amino acids

• Ribosomes – build a cell’s proteins

Endoplasmic Reticulum (ER)

• Involved in production of various materials

• Rough ER – ribosomes attached; involved in protein synthesis

• Smooth ER – no ribosomes; synthesis of lipids and hormones

Golgi Apparatus

• Finishes, sorts and ships cell products

• Specifically… modify and package proteins and lipids into vesicles

• Vesicles often move to and merge with plasma membrane and release their contents outside the cell

Lysosomes• Digestive Compartments• Contain digestive enzymes• Phagocytosis – “eat vessel”

– A formed food vacuole fuses with lysosome

• Types of Vacuoles:– Food Vacuoles– Contractile Vacuoles: pump excess water out of

cell– Central Vacuole: In plants; place to store organic

compounds and as disposal sites for metabolic “wastes” – Provides “turgor pressure” keeping plant cell rigidity so it doesn’t wilt

Mitochondria

• Aerobic Respiration (Creating ATP)

Chloroplasts

• Carry out photosynthesis

• Microtubules – provides support and motility for cellular activities (part of spindle fibers)

• Intermediate filaments: provides support for maintaining shape of cell

• Microfilaments: involved in cell motility (found in muscle cells and cels that move by changing shape)

Flagella and Cilia

• Classified by their length and number per cell…

• Flagella – long and few

• Cilia – short and many

• Both consist of microtubules arranged in a “9+2” array – 9 pairs (doublets) of microtubules arranged in a circle surrounding a pair of microtubules

Cell Walls

• Found in plants, fungi, protists, and bacteria

• Provide support for the cell

• Consists mostly of cellulose (in plants), Chitin (in Fungi)

Peroxisomes

• Break down substnaces

• O2 combines with Hydrogen to form toxic hydrogen peroxide (H2O2)

• Common in liver where they break down toxic substances

Intercellular junctions in animals

• Desmosome – Anchoring Junction

• Tight Junction – form a seal that prevents leakage of extracellular fluid across a layer of cells (i.e. keep the contents of the intestine separate from the body fluid on the oposite side)

• Gap Junction – Communicating junction

See image on page 126

Key differences between plant and animal cells:

1. Plants have cell walls

2. Plants have chloroplasts

3. Plants have large central vacuoles

4. Animal cells have centrioles (microtubule organizing centers)

Membrane Structure and Function

Chapter 8

Evolution of Membrane Models

• Original Davson-Danielli model – Globular Protein sandwich a phospholipid bilayer (proposed in 1935 and accepted until 1970)

• Currently explained by the fluid mosiac model

Fluid Mosaic Model

• It is has mosaic nature of scattered proteins within a flexible matrix of phospholipid molecules.

Plasma Membrane

• Composed of a Phospholipid Bilayer

• Selective Boundary between the cell and its environment (Selectively Permeable)

• Regulates functions of the cell

• Maintains Homeostasis

• Described by Fluid Mosaic model

What makes up the Plasma Membrane?

• Phospholipid Bilayer – hydrophillic heads facing out; hydrophobic tails facing in.

• Proteins – Some as channels to regulate passage of molecules and others as enzymes.

• Cholesterol Molecules – reduce membrane fluidity by reducing phospholipid movement at high temps and hinders solidification at low temps.

• Membrane’s unique composition is suited to specific functions (Mitochondria membranes are embedded with enzymes that function in cellular respiration)

• Carbohydrates – Glycoprotein (protein w/ carb attached) and Glycolipids designate if cell belongs or not… these are called Oligosaccharides.

The fluidity of Membranes:

• Phospholipids can move laterally (frequent) or by the flip-flop (rare)

• Fluid contains unsaturated “tails” with kinks while viscous contains saturated “tails”

Important Components of Plasma Membrane(Important essay concept to address chemistry, structure, and components below)

• Transport Proteins

• Enzymatic Proteins

• Signal Proteins

• Intercellular Joining Proteins

• Cell-cell Recognition Proteins

Traffic Across Membranes

• Substances move in two ways:• Bulk flow: overall movement of a group of

substances

Countercurrent Exchange – movement of substnaces between two regions in which bulk flow movement is in opposite directions. (i.e. blood in fish gills moves opposite direction of surrounding water running past them)

• Constant, Random Motion: motion of the molecules independent from the motion of other molecules

Passive Transport

• Diffusion – movement of molecules from High to low concentration

• Diffusion across a biological membrane is called passive transport.

• Why is it considered passive?• Cell doesn’t need energy to make it

happen• When will this process stop?• When Dynamic Equilibrium is reached

(Homeostasis)

Osmosis

• Osmosis is the passive transport of water across a selectively permeable membrane.

• Osmotic conditions have 3 options:

Isotonic, Hypotonic, or Hypertonic

How many of you have every killed a plant? How?

Over watering or Under watering?

• Isotonic – same concentration of solutes inside as outside cell, not net change

• Hypotonic – low solutes/ high H2O outside cell; H2O moves in -- What does this do to plant and animal cells?

• Animal cells burst; Plant cells swell• Hypertonic – high solutes/ low H2O outside

cell; H2O moves out – What does this do to plant and animal cells?

• Animal cell shrinks; Plant cell contents shrink (loss of turgor pressure)

`

Osmosis

State

H2O

Movement

Solute [ ]

Inside cell

Solute [ ]

Outside Cell

Isotonic[Same] [Same]

Hypotonic [High] [Low]

Hypertonic [Low] [High]

none

Into the cell

Out ofthe cell

Osmosis Questions

• Which situation is best for animal cells? Why?

• Which Situation is best for plant cells? Why?

Passive Transport

• No energy is required to move particles through the cell’s plasma membrane

• [high] to [low]• Facilitated Diffusion

– Protein required to move particles through membrane

– Move down concentration gradient by random movement

– Channel proteins vs. carrier proteins– How glucose enters the cell

Other passive transports:

• Dialysis is the diffusion of solutes across a selectively permeable membrane.

• Plasmolysis is the movement of water out of a cell (osmosis) that results in the collapse of the cell

• Facilitated diffusion – the movement of solutes through channel proteins

Active Transport

• Movement of solutes against a gradient.• [Low] to [High]• Aided by transport proteins (pumps) –

each one is specific to a certain substance• Requires the use of energy (typically ATP)• 67% of energy used to transport Na+ and

K+ across membranes.• See diagram of sodium-potassium pump

(Figure 8.14)

EXOCYTOSIS

• Process of removing large particles or volumes of liquid

• Excretion – removal of waste products

• Secretion – removal of cell products needed elsewhere

• Requires vesicle and energy

ENDOCYTOSIS

• Process in which the plasma membrane engulfs substances from the environment

• Pinocytosis – “cell drinking” large drops of liquid.

• Phagocytosis – “cell eating” large particles are engulfed into a vesicle for digestion

• This is how single celled protists capture food and how white bloods cells work for immunity

• Receptor-mediated endocytosis – specific molecules in the fluid surrounding the cell bond to specialized receptors in the plasma membrane. This then triggers a phagocytosis type process

Questions to look at on AP regarding Membrane Traffic:

• Is the substance moving across a selectively permeable membrane?

• Is the substance of interest water (solvent) or substance (solute)?

• In which direction is the substance moving? Down a gradient or the reverse?

• How does the concentration of solutes vary from one region to another?

• Is energy required to move the substance? Energy is required to go against the gradient

Cell Communication

Chapter 11

Paracrine Signaling

• Acts on nearby “target” cells

• Signal cell discharges molecules into extracellular fluid

• Local signaling

Synaptic Signaling

• Nerve cell communication

• Neurotransmitters released into a synapse

• Local signaling

Hormonal Signaling

• Signals target cells at greater distances.

• Specialized cells secrete hormones into bodily fluid (typically blood).

• Can reach all body cells

• Only specific “target” cells act and respond.

• Plants also use to signal from one part of plant to another

Three stages of cell signaling…

1. Reception – target cell detects an incoming signal from outside cell

2. Transduction:• Changes protein in some way• Converts change to form that can bring specific cellular

response.• Often requires sequence of changes in a series of

different molecules (signal transduction pathway)3. Response – signal finally triggers cell response

(i.e. catalysis by enzyme, rearrangement of cytoskeleton, activation of specific genes…)

• Process ensures the crucial activities occur in the right cells, at the right time, and in proper coordination with other cells

Examples Pathways

• G-protein-linked receptor (11.6 and 11.7)

• Tyrosine-kinase receptor (11.8)

• Ligand-gated ion-channel receptor (11.9)

Signal Transduction Pathways

• Relay signals from receptors to cellular responses

• Protein phosphorylation is a major mechanism of signal transduction (11.10)

• Small molecules and ions are key components of signaling pathways (2nd messengers)– cAMP (11.12)– IP3 (11.14)

Cellular-Responses to Signals

• In response to signal, a cell may regulate activities in the cytoplasm or transcription in the nucleus.

• Elaborate pathways amplify and specify the cell’s response to signals

• Nuclear Response (Figure 11.16)

• Specificity of cell signaling (Figure 11.17)

The Cell Cycle

Chapter 12

Key Roles of Cell Division:

• Functions in reproduction, growth, and repair

How do daughter cells compare to original cell?

• Division distributes identical sets of chromosomes to daughter cells

• Somatic Cells – All body cells except reproductive cells.

• Gametes – sperm and eggs

Important Terms:

• Chromatin:

DNA protein fiber organized into long thin fibers

• Sister Chromatids:

Two chromatids containing identical sets of DNA that are initially attached.

• Centromere:

Location of sister chromatid attachment.

The Cell Cycle

• Occurs in Eukaryotic Cells• Regular pattern of:

– Growth– DNA duplication – cell division

• 4 Stages in the cell cycle:

Gap 1 (G1), Synthesis, Gap 2 (G2), Mitosis• Enzymes control the transfer through the

stages

Gap 1 (G1)

• First Stage (Growth)

• Cell carries out normal functions

• Cell increases in size

• Organelles increase in number

Synthesis

• Second Stage

• Growth and Duplication of DNA

Gap 2 (G2)

• Third Stage

• Similar to G1 phase

• Growth and preparation for cell division.

• Includes a critical checkpoint … the cell will only reproduce if everything is in order.

Mitotic Cycle (Mitosis)

Interphase precedes Mitosis and includes G1,S, and G2

1. Prophase

2. Metaphase

3. Anaphase

4. Telophase

Prophase

1. Nucleoli disappears and chromatin becomes visible chromosomes.

2. Nuclear envelope breaks down.

3. Mitotic spindle is assembled

• Spindle attached to Kinetochore

Metaphase

1. Chromosomes move to the equator

2. Each sister chromatid is attached to its own spindle fiber

3. Spindle fibers are attached to centromere at kinetochore

Anaphase

1. Centromeres are split

2. Sister Chromatids are pulled apart becoming chromosomes

Telophase and Cytokinesis

1. Chromosomes reach opposite poles of the cell

2. Two distinct daughter cells are formed

3. Processes of prophase are reversed

Cleavage Furrow – groove the forms as “purse strings” tightened

Cytokinesis = division of the cytoplasm

Mitosis of a White Fish Blastula Cell

Regulation of the Cell Cycle

Cell-Cycle Control System:

• Cyclically operating set of molecules in the cell the both triggers and coordinates key events in the cell cycle.

Cell-cycle Checkpoints:

• Stop and go-ahead signals regulate the cycle.

• Enzymes drive this process

Cues to regulate Cell Cycle

Internal Signals:

• M-phase checkpoint is the gatekeeper

• Signal that delays anaphase originates at the kinetochores that are not yet attached to spindle microtubules

• External Signals:

• Growth factors are required to stimulate growth

• Density-dependent inhibition – crowded cells stop dividing (12.15)

• Anchorage dependence – to divide, animal cells must be attached to substratum.

Cancer…

• Early in life, cells divide frequently while later in life, cells only grow and divide to replace old cells or repair injuries.

• Cells continue to be regulated by cell cycle and regulation cues

• Cancer cells have escaped cell cycle controls

Key cancer terms

• Metastasis – spread of cancer cells beyond their original state.

• Tumor – mass of abnormal cells within otherwise normal tissue

• Benign tumor – most likely wont cause a serious problem.

• Malignant tumor – invasive enough to impair functions of one or more organs (cancerous tumor)