chapter 3 cell structure and function. what does the cell theory tell us? a cell is the basic unit...

Chapter 3

Cell Structure and Function

What does the cell theory tell us?

• A cell is the basic unit of life

• All living things are made up of cells

• New cells arise from preexisting cells

3.1 What is a cell?

Cellular Organization• Cell = smallest living unit

• Performs all life functions

Why are most cells small?

• Consider the cell surface-area-to-volume ratio:– Small cells have a larger amount of surface

area compared to the volume– An increase in surface area allows for more

nutrients to pass into the cell and wastes to exit the cell more efficiently

– There is a limit to how large a cell can be and be an efficient and metabolically active cell

3.1 What is a cell?

Thinking about surface area to volume in a cell

3.1 What is a cell?

What are some common microscopes used to view cells?

• Compound light microscope– Lower magnification– Uses light beams to view images– Can view live specimens

• Transmission electron microscope– 2-D image– Uses electrons to view internal structure– High magnification, no live specimens

• Scanning electron microscope– 3-D image– Uses electrons to view surface structures– High magnification, no live specimens

3.1 What is a cell?

What are the two major types of cells in all living organisms?

• Prokaryotic cells– Thought to be the first cells to evolve– Lack a nucleus– Represented by bacteria and archaea

• Eukaryotic cells– Have a nucleus that houses DNA– Many membrane-bound organelles

3.2 How cells are organized

What do prokaryotic and eukaryotic cell have in common?

• A plasma membrane that surrounds and delineates the cell

• A cytoplasm that is the semi-fluid (cytosol) portion inside the cell that contains organelles

• DNA

3.2 How cells are organized

Where did eukaryotic cells come from?3.2 How cells are organized

Eukaryotic Cell

Two Categories of Cells

• Sex cells (germ cells):– reproductive cells – male sperm– female oocytes (eggs)

• Somatic cells (soma = body):– all body cells except sex cells

Organelle Functions

The structures and functions of the

cell membrane.

Plasma Membrane: Components

• Phospholipid bilayer

• Cholesterol: resist osmotic lysis

• Carbohydrates

• Proteins

Functions of Plasma (Cell) Membrane

• Physical barrier:– Maintain homeostasis:

• Separates intracellular fluid from extracellular fluid, different conditions in each

• Regulates exchange with environment:– ions and nutrients enter– waste and cellular products released

• Monitors the environment:– extracellular fluid composition– Cell communication and signaling

• Structural support: – anchors cells and tissues


1. Phospholipid Bilayer:– hydrophilic heads—toward watery

environment, both sides– hydrophobic fatty-acid tails—inside

membrane – barrier to ions and water soluble compounds

2. Cholesterol: resist osmotic lysis

3. Carbohydrates: -linked to other molecules as proteoglycans,

glycoproteins, and glycolipids

-Functions

-lubrication & protection

-anchoring & locomotion

-binding specificity

*(acts as receptor)

-self recognition



4. Protein:– ½ mass of membrane– Integral proteins: span width of membrane

• within the membrane

– Peripheral proteins:• Adhere to inner or outer surface of the

membrane

6 Functions of Membrane Proteins

1. Anchoring proteins (stabilizers):– attach to inside or outside structures

2. Recognition proteins (identifiers): – Self identification by immune system

– Label cells normal or abnormal

3. Enzymes: – catalyze reactions in cytosol in extra cellular fluid

4. Receptor proteins:– bind and respond to ligands (ions, hormones) or

signaling, or import/export 5. Carrier proteins:

– transport specific solutes through membrane 6. Channels:

– regulate water flow and solutes through membrane

How things get in and out of cells.

Overcoming the Cell Barrier

• The cell membrane is a barrier, but: – nutrients must get in– products and wastes must get out

• Permeability determines what moves in and out of a cell:

• A membrane that: – lets nothing in or out is impermeable– lets anything pass is freely permeable– restricts movement is selectively permeable

Selective Permeability

• Cell membrane is selectively permeable:– allows some materials to move freely– restricts other materials

• Restricts materials based on:– size– electrical charge– molecular shape– lipid solubility

Selectively Permeable3.3 The plasma membrane and how substances cross it

How do things move across the plasma membrane?

1. Diffusion

2. Osmosis

3. Facilitated transport

4. Active transport

5. Endocytosis and exocytosis

3.3 The plasma membrane and how substances cross it

Solutions

• All molecules are constantly in motion

• Molecules in solution move randomly

• Random motion causes mixing

Concentration Gradient

• Concentration is the amount of solute (glucose) in a solvent (e.g. H20)

• Concentration gradient: – more solute in 1 part of a solvent than another

• Function = Diffusion – molecules mix randomly – solute spreads through solvent – eliminates concentration gradient– Solutes move down a concentration gradient

• From high concentration to low concentration

What are diffusion and osmosis?

• 1. Diffusion is the random movement of molecules from a higher concentration to a lower concentration

• 2. Osmosis is the diffusion of water molecules


How does tonicity change a cell?• Hypertonic solutions have

more solute than the insideof the cell and lead to lysis (bursting)

• Hypotonic solutions have less solute than the inside of the cell and lead to crenation (shriveling)

• Isotonic solutions have equal amounts of solute inside and outside the cell and thus does not affect the cell


What are facilitated diffusion and active transport?

• 3. Facilitated transport is the transport of molecules across the plasma membrane from higher concentration to lower concentration via a protein carrier

• 4. Active transport is the movement of molecules from a lower to higher concentration using ATP as energy; requires a protein carrier


Transport Vesicles

• 5. Endocytosis transports molecules or cells into the cell via invagination of the plasma membrane to form a vesicle

• 6. Exocytosis transports molecules outside the cell via fusion of a vesicle with the plasma membrane


Receptor-Mediated Endocytosis

Figure 3–21

Figure 3–22a

Pinocytosis• Pinocytosis (cell drinking) • Endosomes “drink” extracellular fluid and

enclose it in membranous vesicles at the cell surface– Similar to the steps in receptor-mediated

endocytosis, except that ligand binding is not the trigger

Phagocytosis

• Phagocytosis (cell eating)– pseudopodia (psuedo = false,

podia = feet) – engulf large objects in

phagosomes

Figure 3–22b

Cytoskeleton• A series of proteins that maintain cell shape as well

as anchors and/or moves organelles in the cell• Made of 4 fibers:

– Large microtubules• Forms the foundation of the cytoskeleton• Allows the cell to change shape and assists in mobility

– Thin actin filaments • provide additional strength by attaching the membrane to the

cytoplasm• Attach integral proteins to cytoskeleton• Pairs with thick filaments of myosin for muscle movement

– Medium-sized intermediate filaments• strengthen cell and maintain shape• stabilize position of organelles

Cilia and Flagella• Made of microtubules

• Cilia are about 20x shorter than flagella

• Cilia: Short, numerous– Function: sweep

substances over cell surface

• Flagella: Long, singular– Function: propel cell

through environment

3.5 The cytoskeleton and cell movement

Structures involved in protein production

• Nucleus

• Ribosomes

• Endomembrane system

3.4 The nucleus and the production of proteins

The structure and function of the nucleus


• Nucleus:– largest organelle

• Nuclear envelope:– double membrane

around the nucleus, connected to ER

• Nuclear pores with regulator proteins:– Control exchange of

materials between cytoplasm and nucleus

Within the Nucleus• Nucleoplasm:

– fluid containing ions, proteins (enzymes), DNA, RNA, and nucleoli

• Nucleoli: Dark areas – site of rRNA synthesis and

packaging into ribosomal subunits

• In non-dividing cells DNA is loose Called chromatin

• During Nuclear Division– Chromatin is tightly coiled into

visible chromosomes (23 pairs in humans)

• Chromosomes– tightly coiled DNA (cells

dividing)

The structure and function of ribosomes

• Organelles made of RNA and protein

• Found bound to the endoplasmic reticulum and free floating in the cell

• Site of protein synthesis


The Endomembrane System

• A series of membranes in which molecules are transported in the cell

• It consists of the nuclear envelope, endoplasmic reticulum, Golgi apparatus, lysosomes and vesicles


How does the endomembrane system function and appear?


The parts of the endomembrane system

• Rough endoplasmic reticulum – studded with ribosomes used to make proteins

• Smooth endoplasmic reticulum – lacks ribosomes but aids in making carbohydrates and lipids

• Golgi apparatus – flattened stacks that process, package and deliver proteins and lipids from the ER– Phosphate, carbohydrates, or lipids are attached

• Lysosomes – membranous vesicles made by the Golgi that contain digestive enzymes

• Vesicles – small membranous sacs used for transport

Mitochondria

• A highly folded organelle in eukaryotic cells

• Produces energy in the form of ATP

• They are thought to be derived from an engulfed prokaryotic cell

3.6 Mitochondria and cellular metabolism

Mitochondrial Function: Power House of the Cell

• Aerobic respiration occurs on surface of cristae– takes chemical energy from food (glucose)– With the use of oxygen, Glucose is catabolized

creating CO2 waste to convert ADP into ATP

• Mitochondria supply most of cell’s energy• Have their own DNA (maternal)• Can replicate independent of the cell

Figure 3–9b

glucose + oxygen + ADP carbon dioxide + water + ATP

Carbohydrate Catabolism (Metabolism)

• Carbohydrates are the primary source of cellular energy for most organisms

• Glucose is the most commonly used carbohydrate and will always be used first

• Generates ATP and other high-energy compounds by breaking down carbohydrates:glucose + oxygen carbon dioxide + water

Carbohydrate Catabolism (Metabolism)

Two methods for ATP productions via catabolism ofglucose

1. Cellular Respiration Aerobic reactions: - Requires oxygen to serve as the final electron acceptor

- Generate ATP in ETC

- Most efficient method of ATP production- 1 glucose generates 36 ATP

- Involves reaction performed inside the mitochondria

2. Fermentation Anaerobic reactions- Requires an organic molecule (carbon based) to serve as the final

electron acceptor- Can be done in the absence of oxygen- ATP is synthesized using glycolysis

- Less efficient, 1 glucose generates 2 ATP

- In humans, results in lactic acid

Enzymes are important for cellular respiration and many activities in the cell

• Most enzymes are proteins• Enzymes are often named for the molecule that

they work on or substrates• Enzymes are specific to what substrate they

work on• Enzymes have active sites where a substrate

binds• Enzymes are not used up in a reaction but

instead are recycled• Some enzymes are aided by non-protein

molecules called coenzymes


How do enzymes work?


What is cellular respiration?

• Production of ATPin a cell

• Includes:1. Glycolysis

2. Citric acid cycle

3. Electron transport chain


What happens in glycolysis – step 1 of cellular respiration?

• Glycolysis – Occurs in the cytoplasm– Breaks glucose into 2 pyruvate– NADH and 2 ATP molecules are made– Does not require oxygen



• Citric acid cycle– A cyclical pathway that occurs in the

mitochondria– Produces NADH and 2 ATP– Requires oxygen



• Electron transport chain– Series of molecules embedded in the

mitochondrial membrane– NADH made in steps 1 and 2 carry electrons

here– 32-34 ATP are made depending on the cell– Requires oxygen as the final electron

acceptor in the chain


Oxygen is needed as the Final Electron acceptor in the ETC

- At the end of the chain the electrons are accepted by oxygen creating an anion (O-) inside, which has a strong affinity for the cations (H+) outside.

- Chemiosmosis generates ATP:

- H+ from the outside moves toward O- on the

inside through special membrane channels

that are coupled to ATP synthase

- High-energy diffusion of H+ drives the reaction

ADP + P ATP.

- H+ combines with O- inside the mitochondria creating water (H2O)

Oxidative Phosphorylation

Figure 25–5b

Occurs on a membrane, the mitochondrial cristae, to generate most of the ATP produced from glucose

What other molecules besides glucose can be used in cellular respiration?

• Other carbohydrates

• Proteins

• Lipids

• Nucleic Acids


Lipolysis – Lipid Catabolism• Hydrolyzes triglycerides (fat storage) glycerol and three fatty acids• Glycerol:

– Glycerol pyruvic acids in the cytoplasm– Pyruvic acid catabolized through TCA in mitochondria

• Fatty Acids:– Fatty acids are catabolized– Enter the TCA as two-carbon fragments– For each two-carbon fragment of fatty acid produced by

beta-oxidation, the cell can generate 17 molecules of ATP• This is 1.5 times the energy production as with

glucose• Generates more energy but requires more oxygen

– Occurs much more slowly than equal carbohydrate metabolism

Protein and Amino Acid Catabolism

1. Protein amino acids2. Amino group (-NH2) is removed from amino acid

in process called deamination– Requires vitamin B6

3. Amino group is removed with conjunction with a hydrogen creating ammonia (NH3)– Toxic

4. Liver converts the NH3 urea– Harmless and excreted by the kidney

5. Remaining amino acid carbon chains are used at various stages in the Citric Acid Cycle to generate ATP– Amount of ATP produced varies

Amino Acid Catabolism

Figure 25–10 (Navigator)

Protein and Amino Acid Catabolism

• Not a Practical Source of Quick Energy • Typically only used in starvation situations• Harder to break apart than carbohydrates or

lipids• Proteins are structural and functional parts of

every cell– Thus tend to only be used when no other energy

source is available• Amino acids are simply recycled by hydrolysis of

peptide bonds in one protein, to be reassembled by dehydration synthesis into the next.

Nucleic Acid Catabolism• DNA is never catabolized for energy• RNA can be broken down into:

– Simple sugars– Nitrogenous bases

• Sugars:– Metabolized in glycolysis but only the pyrimidine bases

(uracil and cytosine) can be processed in the TCA cycle• Purines (adenine and guanine) are deaminated and excreted as uric

acid making RNA metabolism very inefficient

• Typically nucleotides are simply recycled into new nucleic acid molecules and are not used for energy production

chapter 3 cell structure and function. what does the cell theory tell us? a cell is the basic unit...

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