1/25/2016

1

Learning Objectives

Describe what a cell is and the two general types of cells.

Describe the structure and functions of cell membranes.

Describe several ways in which molecules move across membranes.

Describe how cells are connected and how they communicate with each other.

Describe nine important landmarks in eukaryotic cells.

Chapter 3: Cells Cell Theory1. All living organisms are made up of one

or more cells.

2. All cells arise from other pre-existing cells.

The cell: The smallest unit of life that can function independently and perform

all the necessary functions of life, including reproducing itself.

Cells

Robert Hooke, a British scientist, mid-1600s

A cell is a three-dimensional structure, like a fluid-filled balloon, in which many of the essential chemical reactions of life take place.

Nearly all cells contain DNA (deoxyribonucleic acid).

Prokaryotic cells are structurally simple, but there are many types of them.

Every cell falls into one of two basic categories:

1. A eukaryotic cell

• has a central control structure called a nucleus, which

contains the cell’s DNA.

• eukaryotes

2. A prokaryotic cell

• does not have a nucleus; its DNA simply resides in the middle of the cell.

• prokaryotes

1/25/2016

2

Eukaryotic cells have compartments with specialized functions: organelles

Which feature below is not found in a prokaryote?

1. Plasma membrane

2. Nucleus

3. Ribosomes

4. Cell wall

5. Flagellum

Endosymbiosis Theory

Developed to explain the presence of two organelles in eukaryotes, chloroplasts in plants and algae, and mitochondria in plants and animals.

Humans may be part bacteria

Which answer below supports the theory that mitochondria and chloroplasts were originally bacteria?

1. Circular DNA is present in both organelles.

2. Both organelles are larger than other organelles in the cell.

3. Both organelles are surrounded by a single lipid bilayer.

4. All of the above.

1/25/2016

3

Every cell is bordered by a plasma membrane. Plasma membranes are complex structures?

They perform critical functions

• take in food and nutrients

• dispose of waste products

• build and export molecules

• regulate heat exchange

• regulate flow of materials into and out of cell

Molecules embedded within the plasma membrane help it perform its functions.

Which arrow indicates a protein or part of a protein that is hydrophobic?

1. Arrow A

2. Arrow B

3. Arrow C

4. Arrow D

A

B

C

D

There are four primary types of membrane proteins, each of which performs a different function.

1/25/2016

4

The Plasma Membrane “Fluid Mosaic”

In addition to proteins, two other molecules are found in the plasma membrane:

1. Short, branched carbohydrate chains

2. Cholesterol

Lipids that make up the cell membrane are hydrophobic. Hydrophilic molecules, like glucose, cannot cross this barrier. What major component of the plasma membrane helps glucose get into and out of the cell?

1. Phospholipids

2. Carbohydrates

3. Nucleic acids

4. Proteins

5. Fatty acids

Which protein found on the plasma membrane likely contributes to rejection of a transplanted organ or tissue?

1. Receptor proteins

2. Recognition proteins

3. Transport proteins

4. Enzymatic proteins

Membrane surfaces have a

“fingerprint” that identifies the cell.

Cells with an improper fingerprint are recognized as foreign and are attacked by your

body’s defenses.

Molecules move

across membranes

in several ways. There are two types of passive transport:

1. Diffusion

2. Osmosis

Passive transport is the spontaneous diffusion of molecules across a membrane.

1/25/2016

5

Diffusion and Concentration Gradients

• Solutes

• Solvents

Molecules move down their

concentration gradient

Facilitated Diffusion

Most molecules can’t get through plasma membranes on their own.

Carrier molecules

• transport proteins

Summary

In passive transport – which includes simple and facilitated diffusion and osmosis – the molecular movement occurs spontaneously, without the input of energy.

This occurs as molecules move down their concentration gradient.

Osmosis is the passive diffusion of water across a membrane.

Cells in Solution Tonicity

• the relative concentration of solutes outside of the cell relative to inside the cell

Hypertonic

Hypotonic

Isotonic

1/25/2016

6

The Direction of Osmosis

Determined only by a difference in total concentration of all the molecules dissolved in the water

It does not matter what solutes they are.

Milk of magnesia and magnesium salts

Water moves via osmosis from the cells into the intestines.

How do laxatives relieve constipation?

An amoeba (a single-celled protist) is placed in a solution. The volume of the cell increases (cell swells). Which statement below is the correct interpretation of this result?

1. The amoeba is in a hypertonic solution.

2. Water is moving into the amoeba.

3. The amoeba is in a isotonic solution.

4. Water is moving out of the amoeba.

In active transport, cells use energy to move small molecules.

Two distinct types of active transport:

1. Primary

2. Secondary

Primary active transport:uses energy directly from ATP

Secondary Active Transport The transport protein simultaneously

moves one molecule against its concentration gradient while letting another flow down its concentration gradient.

No ATP is used directly. At some point energy from ATP was used

to pump one of the types of molecules involved against their concentration gradient.

A normal cell has a high concentration of potassium on the inside and a low concentration of potassium on the outside. Also, a normal cell has a low concentration of sodium on the

inside and a high concentration on the outside. Yet, the net movement of potassium is into the cell and the net movement of sodium is out of the cell. What type of transport is involved?

1. Osmosis

2. Facilitated transport

3. Active transport

4. Simple diffusion

5. Secondary active transport

1/25/2016

7

An intestinal epithelial cell powers the movement of glucose into the cell against its concentration gradient by simultaneously transporting sodium down its concentration gradient. Which transport mechanism is responsible?

1. Osmosis

2. Facilitated transport

3. Active transport

4. Simple diffusion

5. Secondary active transport

Endocytosis and exocytosis are used for bulk transport of particles.

Three types of endocytosis:1. Phagocytosis

– Cell Eating

2. Pinocytosis

– Cell drinking

3. Receptor-mediated endocytosis

– Lots of small particles

When a woman nurses her baby, proteins are released from the mammary cells, accumulate in the ducts of the breast, and flow out of the nipple. Which process listed below is involved?

1. Phagocytosis

2. Pinocytosis

3. Receptor-mediated endocytosis

4. Exocytosis

1/25/2016

8

Connections between cells hold them in place and allow communication with each other Tight Junctions

form continuous, water-tight seals around cells and also anchor cells in place

particularly important in the small intestine where digestion occurs

Desmosomes

are like spot welds or rivets that fasten cells together into strong sheets

function like Velcro: they hold cells together but are not water-tight

found in much of the tissue-lining cavities of animal bodies

Gap Junctionspores surrounded by special proteins that form

open channels between two cells

Gap junctions are an important mechanism for cell-to-cell communication.

Your skin cells form a waterproof barrier, therefore they are held together by…

1. Tight junctions

2. Desmosomes

3. Gap junctions

4. Glue

Plasmodesmata

Tube-like channels connecting the cells to each other and enabling communication and transport between them

Consider a plant as one big cell?

1/25/2016

9

Nine important

landmarks

distinguish

eukaryotic

cells.

The nucleus is the cell’s genetic control center.

The nucleus―the largest and most prominent organelle in most eukaryotic cells.

The nucleus has two primary functions:

• genetic control center

• storehouse for hereditary information

Chromatin - a mass of long, thin

fibers consisting of DNA & proteins

Nucleolus

an area near the center of the nucleus where subunits of the ribosomes are assembled

Ribosomes are factories for proteins.

Shape (support), intracellular movement, and cell Movement

Cytoskeleton: Three Chief Purposes

Cilia and FlagellumWhich type of cytoskeletal protein is involved in the tail movement of a swimming human sperm (flagella)?

1. Microtubules

2. Intermediate filaments

3. Microfilaments

1/25/2016

10

Bag-within-a-Bag Structure:the intermembrane space and the matrix

Mitochondria: the cell’s energy convertersEndosymbiosis

Mitochondria may have existed as separate single-celled, bacteria―like organisms billions of years ago.

Mitochondria have their own DNA!

Lysosomes are the cell’s garbage collectors

•Round, membrane-enclosed, acid-filled vesicles•Digestive system of the cell

Why is Tay-Sachs (Genetic disorder)

disease like a strike by trash collectors?

50 different enzymes necessary for lysosomes to function well

Malfunctions sometimes occur

Lipid-digesting enzyme made incorrectly

Lipid buildup in cells

The Endomembrane System

Where cells build proteins and disarm toxins

Rough Endoplasmic Reticulum

1/25/2016

11

The Smooth Endoplasmic Reticulum Critical Responsibilities of the Smooth ERAnother critical responsibility of the smooth ER—particularly the smooth ER in human liver cells—is to help protect us from dangerous molecules that get into our bodies.

Alcohol, antibiotics, barbiturates, amphetamines, and other stimulants, along with toxic metabolic waste products produced in our bodies, are made less harmful by detoxifying enzymes in the smooth ER

Which organ below is likely composed of cells with the greatest amount of SER?

1. Heart

2. Lungs

3. Kidney

4. Liver

5. Brain

The Golgi apparatus processes products and ships them throughout the body.

The cell wall provides additional protection and support for plant cells.

Vacuoles: multipurpose storage sacs for cells

1. Nutrient storage

2. Waste management

3. Predator deterrence

4. Sexual reproduction

5. Physical support

The central vacuole can play an important role in five different areas of plant life:

1/25/2016

12

Chloroplasts: the plant cell’s solar power plant The stroma and

interconnected little flattened sacs called thylakoids (stack called a granum)

Endosymbiosis Theory Revisited

Chloroplasts resemble photosynthetic bacteria

Circular DNA

Dual outer membrane

Almost all eukaryotic organisms derive energy directly or indirectly from the sun. Therefore, which organelle is the most important for life as we know it?

1. Nucleus

2. Endoplasmic reticulum

3. Golgi

4. Chloroplast

5. Mitochondria

Learning Objectives

Understand and be able to explain the following:

How energy flows from the sun and through all life on earth

How photosynthesis uses energy from sunlight to make food

How cellular respiration converts food molecules into

ATP, a universal source of energy

Alternative pathways to energy acquisition

Chapter 4: Energy

Energy flows from the

sun and through all life

on earth.

Biofuels and Fossil Fuels Chains of carbon and hydrogen atoms

• Energy is stored in the bonds

Animal fats and oils

How do fuels provide energy?

The activities of living organisms are fueled by breaking chemical bonds and harnessing the released energy.

1/25/2016

13

Energy Conversions

All life depends on capturing energy from the sun and converting it into a form that living organisms can use.

Two key processes

• Photosynthesis

• Cellular respiration

Plants convert the energy of the sun into _______ bonds in carbohydrates using a process called________.

1. Covalent bonds; photosynthesis

2. Ionic bonds; photosynthesis

3. Hydrogen bonds; cellular respiration

4. Covalent bonds; cellular respiration

5. Ionic bonds; cellular respiration

What is energy?

The capacity to do work

Work

• Moving matter against an opposing force

Water flowing through a dam can be used to generate electricity, which is an example of…

1. Energy being used to do work

2. Kinetic energy

3. Potential energy

4. 1 and 2

5. 2 and 3

Energy Conversions Only ~1% of the energy released by the sun that

earth receives is captured and converted by plants.

• Converted into chemical bond energy

What happens to the other 99%?

As energy is captured and converted, the amount of energy available to do work decreases.

1/25/2016

14

Thermodynamics

First Law of Thermodynamics

Energy can never be created or destroyed. It can only change from one form to another.

Second Law of Thermodynamics

Conversion of energy includes the transformation of some energy into heat.

Heat is almost completely useless to living

organisms.

Given that every energy conversion is inefficient, which type of food below would feed the most people?

1. Steak

2. Fish

3. Rice

4. Ice cream

How do cells directly fuel their chemical reactions?

None of the light energy from the sun can be used directly to fuel cellular work.

First it must be captured in the bonds of a molecule called adenosine triphosphate

(ATP).

Structure of ATP

Adenosine Triphosphate

Pop off the third phosphate group• ATP ADP + Phosphate group + energy release

Release a little burst of energy!

Use this energy to drive chemical reactions necessary for cellular functioning.

• Building muscle tissue

• Repairing a wound

• Growing roots

Recycling in the CellADP + phosphate group + energy = ATP

ATP molecules are like rechargeable batteries cells.

1/25/2016

15

Which answer is an example of potential energy?

1. Heat

2. Converting ATP to ADP

3. A candy bar

4. ATP

5. 3 and 4

Where does plant matter come from? Photosynthesis: the big picture.

From a seed

to a tree: Where does the mass come from?

Photosynthetic Organisms Photosynthesis: The Big Picture

3 inputs

2 products

Photosynthesis take place in the chloroplasts.

Organelles found in plant cells

A Closer Look at Chloroplasts

1/25/2016

16

Light energy travels in waves: plant pigments absorb specific wavelengths.

Light Energy A type of kinetic energy

Made up of little energy packets called photons

Different photons carry different amounts of energy, carried as waves.

Shorter waves = more energy.

Electromagnetic Spectrum

Range of energy that is organized into waves of different lengths.

Shorter the wavelength, higher the energy.

Visible Spectrum

Range of energy humans see as light

ROYGBIV

Pigments = molecules that absorb light

Red, Orange, Yellow, Green, Blue, Indigo, Violet

UV light can damage the DNA in your cells, while visible light cannot. Why?

1. UV light has a longer wavelength than visible light.

2. The wavelength of UV light is within the visible spectrum.

3. UV light contains more energy than visible light.

4. UV light contains less energy than visible light.

Chlorophyll Plant pigment

Absorbs certain wavelengths of energy (photons) from the sun - can only absorb specific wavelengths of energy.

Therefore, plants produce several different types of pigments

Absorbed energy excites electrons

Plant Pigments Chlorophyll a

Chlorophyll b

Carotenoids

1/25/2016

17

Why are leaves of deciduous trees not green in the fall?

1. Less green light is reflected due to less chlorophyll.

2. More green light is reflected due to increased carotenoids.

3. More red, orange, yellow light is reflected due to carotenoids.

4. 1 and 3

Electron Excitation

Conversion of electromagnetic energy into chemical energy of bonds between atoms

Photons of specific wavelengths bump electrons up a quantum level into an excited state

Photons cause electrons in chlorophyll to enter an excited state.

Two Potential Fates of Excited Electrons

1) Electron returns to resting, unexcited state.

2) Excited electrons are passed to other atoms.

1/25/2016

18

The Passing of Electrons in Their Excited State

Chief way energy moves through cells

Molecules that gain electrons always carry greater energy than before receiving them

• Can view this as passing of potential energy from

molecule to molecule

Photosynthesis in detail: the energy of sunlight is captured as chemical energy.

FOLLOW THE ELECTRONS!

The “Photo” Part Sunlight ATP A high-energy electron carrier

Electrons That Leave the Photosystem Are Replenished

Where does oxygen come from?

An Electron Transport Chain

Connects the two photosystems

1/25/2016

19

Product #1 of the “Photo”Portion of Photosynthesis:

ATP

The Second Photosystem

Follow the electrons

Product #2 of the “Photo”Portion of Photosynthesis:

NADPH

Products from the“Photo” Portion

ATP and NADPH

Time for the “synthesis” part!

Plants produce oxygen…

1. during electron transport in photosystem 1.

2. during electron transport in photosystem 2.

3. by splitting water to replace electrons in chlorophyll a.

4. by splitting water to replace electrons in the electron transport chain.

Review: Which answer is an example of a molecule with high potential energy?

1. NADPH

2. ATP

3. NADP+

4. H2O

5. Both 1 and 2

1/25/2016

20

“SYNTHESIS”

Photosynthesis in detail: the captured energy of sunlight is used to make food.

The Calvin Cycle

Series of chemical reactions

Occurs in stroma

Enzymes are recycled

The Processes in the Calvin Cycle Occur in Three Steps:

What component of photosynthesis is directly responsible for the increased weight of the plant?

1. Photosystem 1 providing ATP

2. Photosystem 2 providing NADPH

3. Calvin Cycle fixing carbon

Evolutionary Adaptations

Some plants thrive in hot, dry conditions

Adaptations that reduce evaporative water loss

• How do plants use water?

Stomata

Pores for gas exchange

How to get CO2 when stomata are shut?

1/25/2016

21

C4 Photosynthesis

• C4 plants produce ultimate “CO2-sticky tape” enzyme.

• C4 photosynthesis adds an extra set of steps.

CAM Photosynthesis

Close stomata during hot dry days

At night, stomata open, CO2 let in and temporarily bound to a holding molecule

During day, CO2 gradually released and used while stomata are closed

All Three Photosynthetic Pathways

1/25/2016

22

Reminder: The energy used by plants and animals ultimately came from…

1. Food

2. Soil

3. Sun

4. Air

How do living organisms fuel their actions? Cellular respiration: the big picture.

Cellular Respiration

The big picture

ATP: Food molecules into ATP by cellular respiration

Three-Step Process

Biggest ATP“payoff” (90%) occurs during the electron transport chain.

Cellular Respiration

Requires (1) fuel and (2) oxygen.

Potential energy stored in chemical bonds of sugar, protein, and fat molecules.

Breaks bonds to release the high-energy electrons captured in ATP.

Oxygen is electron magnet.

A Human Example

Eat food

Digest it

Absorb nutrient molecules into bloodstream

Deliver nutrient molecules to the cells

At this point, our cells can begin to extract some of the energy

• stored in the bonds of the food molecules

1/25/2016

23

The first step of cellular respiration: glycolysis is the universal energy-releasing pathway.

Glycolysis: the universal energy-releasing pathway

Glycolysis

Three of the ten steps yield energy

– quickly harnessed to make ATP.

High-energy electrons are transferred to NADH.

Net result:

each glucose molecule broken down into two molecules of pyruvate

ATP molecules produced

NADH molecules store high-energy electrons

The Preparatory Phaseto the Krebs Cycle

Payoff from the Krebs Cycle:

ATP

NADH

FADH2

1/25/2016

24

Two key features of mitochondria are essential to their ability to harness energy from molecules:

• Feature 1: mitochondrial “bag-within-a-bag” structure

• Feature 2: electron carriers organized

within the inner “bag”

The third step in cellular respiration: ATP is built in the electron transport

chain. In the mitochondria:

The “Bag-within-a-Bag”

Follow the Electrons

Proton (H+) concentration gradient represents a significant source of potential energy!

Proton Gradientsand Potential Energy

The force of the flow of H+ ions fuels the

attachment of free-floating phosphate groups to ADP to produce ATP.

Why can a proton gradient be used to make ATP?

1. The movement of protons from high to low concentration provides kinetic energy to make ATP from ADP.

2. The movement of protons from low to high concentration provides kinetic energy to make ATP from ADP.

3. The movement of protons from high to low concentration

provides the potential energy to make ATP from ADP.

4. The movement of protons from low to high concentration provides the potential energy to make ATP from ADP.

1/25/2016

25

Plants have both chloroplasts and mitochondria. Why?

1. The mitochondria also synthesize sugars.

2. The mitochondria are used to convert oxygen to carbon dioxide for the plant.

3. The mitochondria break down sugars produced by photosynthesis to provide energy for the cellular work of the plant.

4. The mitochondria break down fat produced by photosynthesis to provide energy for the cellular work of the plant.

There are alternative

pathways to energy

acquisition.

Beer, wine, and spirits are by-products of cellular metabolism in the absence of oxygen.

1/25/2016

26

Which activity below would produce lactic acid via anaerobic respiration?

1. Running 10 miles

2. Swimming 1 mile

3. Sprinting 100 meters

4. Making beer

5. 3 and 4

Eating a complete diet: cells can run on protein and fat as well as on glucose.