Chapter 2 What is life? Picture removed. First meteorite, ALH84001 Discovered by Roberta Score in...

Chapter 2What is life?

Picture removed

First meteorite, ALH84001

• Discovered by Roberta Score in 1984• 4.5 billion years old- came from Mars• Claimed to prove evidence of Martian life

inside the meteorite• News report “Life on Mars”, President had a

press conference• Other scientists said NO signs of life• NASA had overblown its findings

NASA Signs of life

• One of NASA’s goals is to search for life as it occurs on earth- 1964

• NASA would like for chemical information in the soil- gases, nutrients– Initial results said yes

• Looking for chemical reactions• NASA used our definitions of what living things

do– Five common functional traits of life

What is Life?

Scooby says “Life is about being happy and making people laugh”

All living things have some functional traits in common

• Living things have five functional traits in common:

– Growth: for unicellular (one-cell) organisms, this is an increase in cell size prior to reproduction; for multicellular organisms, this is an increase in an organism’s size as the number of cells making up the organism increases.


• Living things have five functional traits in common:– Reproduction: the process of producing new

organisms.


• Living things have five functional traits in common:– Homeostasis: the maintenance of a relatively

constant internal environment.


• Living things have five functional traits in common:– Sense and response to stimuli: organisms respond to

stimuli in many ways – they may move toward a food source or away from a threatening predator


• Living things have five functional traits in common:– Ability to obtain and use energy: all living

organisms require an input of energy to power their activities, and chemical reactions convert that energy into usable forms.


• Energy is the ability to do work. Living organisms obtain energy from food, which they either make from sunlight (plants) or consume from the environment (animals).

• Chemical reactions convert that energy into usable forms. Metabolism is the sum total of all of the chemical reactions taking place in the cells of a living organism that allow it to obtain and use energy.

At its most basic level, all life is composed of chemicals

• All life use the same basic chemical recipe.

• Approximately 100 elements are found on earth.

• Elements are substances that cannot be broken down by chemical means into small substances. They are components of matter.

• Matter is anything that takes up space and has mass.

Look at Infograph 2.2


• Atoms have distinct chemical properties determined by the number of subatomic particles the atom has.

Infographic 2.2


• Elements exist as atoms – the smallest units of an element that cannot be chemically broken down into smaller units.


• The nucleus is the dense core of an atom.


• Protons are positively charged subatomic particles found in the nucleus of an atom.


• Electrons are negatively charged subatomic particles with negligible mass.


• Neutrons are electrically uncharged subatomic particles found in the nucleus of an atom.


• The periodic table of elements represents all known elements on earth.

• Each element is placed in order on the periodic table of elements by its atomic number, the number of protons found in the nucleus of its corresponding atom.

Atoms consist of protons, neutrons, and electrons

• Elements differ in their number of protons, neutrons, and electrons

• Helium has two protons, two neutrons, and two electrons

• Carbon has six protons, six neutrons, and six electrons

Copyright © 2009 Pearson Education, Inc.

Carbon is a versatile component of life’s molecules

• Carbon is the fourth most common element in the universe and the second most common element in your body.– Just six elements make up the bulk of you:

• Oxygen (65%) • Carbon (18.5%) most found after decay• Hydrogen (9.5%)• Nitrogen (3.3%)• Phosphorus and sulfur (2%)


• The atomic mass of an atom is determined by adding the number of protons and neutrons.

Atomic Mass– Carbon with 6 protons has an atomic number of 6 – Carbon has 6 neutrons– The mass number (atomic weight) is the sum of the

protons and neutrons in the nucleus (carbon-12 is written 12C)


• Carbon is a key component of the molecules of living organisms because it can form multiple covalent bonds – strong chemical bonds resulting from the sharing of a pair of electrons between two atoms.

• Electrons are the only subatomic particles involved in chemical bonding – First level holds two electrons– Second level holds eight electrons– Third level holds eight electrons

Carbon forms Covalent Bonds

• http://www.youtube.com/watch?v=j1e-f1W-0UA&feature=related

Diagram element of Carbon

• 6 protons• 6 electrons• 6 neutrons• What is the atomic number?• What is the atomic mass?


• When atoms are linked by covalent bonds, they form molecules. Carbon atoms have four potential binding sites and can therefore bind up to four different atoms.

Covalent Bonds with Carbon

• Covalent Bond– Sharing of electrons

• Carbon can bind with four different elements• Organic molecules can make long chains of

carbons with hydrogens


• Living things are made of organic molecules. Glucose, fats, etc.

• Organic molecules have carbon-based backbones and at least one C-H bond.


• Inorganic molecules lack carbon-based backbones and C-H bonds.

• 0-C-0. Doesn’t have a C-C or C-H backbone• H2O

NASA

• Astrobiologists talk about carbon-based life forms they are talking about organic molecules (C-C or C-H bonds)

Molecules of life• Four types of complex organic molecules or

polymers that make up living things on earth:– Carbohydrates

• Polymers made up of linked monomers called monosaccharides

– Proteins• Proteins are made up of amino acids

– Lipids (not a true polymer)• Lipids are made of fatty acids and glycerol

– Nucleic acids• Polymers composed of nucleotides

Molecules of life

• Carbohydrates, proteins, lipids, and nucleic acids are macromolecules

• Large organic molecules that make up living organisms

• NASA’s Viking probe did not find any of these life-defining organic molecules in the Martian soil

• No living organisms

NASA

• Final conclusion• Meteorite definitely came from Mars• Organic molecules not present in Martian soil but

present in the meteorite• Meteorite likely came from beneath the surface of

Mars• Is there life beneath the surface????• Besides organic molecules, what else was found in

the meteorite?

Molecules of life

• Macromolecules share a similar organization – they are composed of monomers (one chemical subunit) linked together to form a polymer (a molecule made up of monomers linked together in a chain).

Molecules of life: Carbohydrates• Carbohydrates are organic molecules made up of one or

more sugars.• Carbohydrates are polymers made up of monosaccharide

monomers.

CARBOHYDRATES

– Sugar monomers or one sugar carbohydrates are called monosaccharides, such as glucose and fructose

– Primary function in energy storing. Main fuel for cellular work

– Also used as raw materials to manufacture other organic molecules

– Quick energy for 24 hours


Complex carbohydrates

• Two monosaccharides (monomers) can bond to form a disaccharide– Linked by covalent bond– An example is a glucose monomer bonding to a fructose monomer to form

sucrose, a common disaccharide– Table sugar is sucrose (glucose and fructose)– Malt sugar for beer is maltose

– Combination of glucose and glucose– Lactose, milk sugar (galactose and glucose)


Complex Carbohydrates

• Polysaccharides are polymers of monosaccharides– They can function in the cell as a storage molecule or

as a structural compound– Linked together by covalent bonds


3.7 Polysaccharides are long chains of sugar units

• Starch is a storage polysaccharide composed of glucose monomers and found in plants– Potatoes, rice, pasta

• Glycogen is a storage polysaccharide composed of glucose, which is hydrolyzed by animals when glucose is needed– Liver for sugar storage for one day only


• Cellulose in human food passes through the digestive tract as insoluble fiber

• Humans cannot digest cellulose– Some microbes use enzymes to digest cellulose– Many herbivores, from cows to termites, have

symbiotic relationships with these microbes

Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

• Chitin, another structural polysaccharide, is found in the exoskeleton of arthropods


What is high-fructose corn syrup and is it to blame for obesity?

• When you drink a soda, you are probably consuming a sweetener called high-fructose corn syrup (HFCS)

• Because fructose is sweeter than glucose – This is used to sweeten sodas– So, if you overconsume sweeteners as well as fat

and do not exercise, you may experience weight gain


Molecules of life: Proteins• Proteins are organic molecules made up of

amino acid subunits.– 20 different amino acids– Core structure, have an amino group and a

carboxyl group– Linked together into a three-dimensional

structure

Proteins are essential to the structures and functions of life

• Structural proteins are found in hair and fibers that make up muscles and tendons

• Defensive proteins include antibodies of the immune system

• Transport proteins carry oxygen


A protein’s specific shape determines its function

• A polypeptide chain contains hundreds or thousands of amino acids linked by peptide bonds– The amino acid sequence causes the polypeptide to assume a

particular shape– The shape of a protein determines its specific function– Proteins do not function properly until they fold up into their unique

three-dimensional shape


Molecules of life: Lipids• Lipids are organic molecules that generally are hydrophobic – they don’t mix with

water. There are different types of lipids, each with a distinct structure and function.• Not a true polymer• Function

– Energy storage. 2x as much as carbohydrate. Long-term storage of energy

Lipids• Different types of lipids with distinct structure

and function• Not made of repeating subunits or building

blocks (not a true polymer)• Hydrophobic molecules

– Do not mix with water

• Function– Energy storage. 2x as much as carbohydrate.

Long-term storage of energy

Three main groups of Lipids

• Fatty acids– Unsaturated- with double bonds– Saturated – without double bonds

• Triglycerides (fats)• Sterols (steroids)• Phospholipids

3.8 Fats are lipids that are mostly energy-storage molecules

• Triglycerides or fats are lipids made from glycerol and fatty acids

• Three fatty acids chains attached to one glycerol• Padding, cushioning organs, thermal insulation


3.8 Fats are lipids that are mostly energy-storage molecules

• Some fatty acids contain double bonds– This causes kinks or bends in the carbon chain– These compounds are called unsaturated fats

– Fats with the maximum number of hydrogens or no double bonds are called saturated fats


Fig. 5-12b

(b) Unsaturated fat

Structural formulaof an unsaturatedfat molecule

Oleic acid, anunsaturatedfatty acid

cis doublebond causesbending

Fig. 5-12a

(a) Saturated fat

Structuralformula of asaturated fatmolecule

Stearic acid, asaturated fattyacid

• Fats made from saturated fatty acids are called saturated fats, and are solid at room temperature

• Most animal fats are saturated (lard, butter, etc.)– Fats made from unsaturated fatty acids are called

unsaturated fats or oils, and are liquid at room temperature

– Plant fats and fish fats are usually unsaturated– Liquid vegetable oils


What are trans fats?

• Bonus question on test 1

3.9 Phospholipids and steroids are important lipids with a variety of functions

• Phospholipids are structurally similar to fats and are an important component of all cells– For example, they are a major part of cell membranes,

in which they cluster into a two layers of phospholipids– The hydrophilic heads (water loving) are in contact with

the water of the environment and the internal part of the cell

– The hydrophobic tails band in the center of the bilayer


Water

Hydrophobictails

Hydrophilicheads

Water

3.9 Phospholipids and steroids are important lipids with a variety of functions

• Sterols or Steroids are lipids composed of four fused ring structures– Cholesterol is an example of a steroid that plays a

significant role in the structure of the cell membrane– In addition, cholesterol is the compound from which

we synthesize sex hormones


3.10 CONNECTION: Anabolic steroids pose health risks

• Anabolic steroids are synthetic variants of testosterone that can cause a buildup of muscle and bone mass– They can be sold as prescription drugs and used to

treat certain diseases (damage to organs)– They may also be abused with serious consequences,

such as liver damage that can lead to cancer


Phospholipids define cell boundaries• Cells are the basic structural units of

living organisms.• Cells are bounded by a cell membrane –

a double layer (bilayer) of phospholipids that forms the boundary of a cell, separating the contents of a cell from its environment.

Phospholipids define cell boundaries

• Phospholipids assemble into bilayers in water. • Water-hating tails congregate between water-loving heads. • This phospholipid bilayer forms a semi-permeable barrier

to substances on either side of it.

NUCLEIC ACIDS

Storage, transmission, and execution of genetic instructions.

3.16 Nucleic acids are information-rich polymers of nucleotides

• Nucleic Acids – DNA (deoxyribonucleic acid) and RNA (ribonucleic

acid) are composed of monomers called nucleotides– Five different nucleotides (A, T, C, G, U)– Nucleotides have three parts

– A sugar– A phosphate group– A base


Properties of water

• All of life’s chemical reactions take place in water, and many living things can survive only a few days without it.

Properties of water

• Water is a universal solvent (a substance in which other substances can dissolve).

• Water transports all of life’s dissolved molecules, or solutes, from place to place, making life essentially a water-based solution.

Overview: The Molecule That Supports All of Life

• Water is the biological medium on Earth. ¾ or Earth’s surface is submerged in water– All living organisms require water more than any

other substance– Most cells are surrounded by water, and cells

themselves are about 70–95% water– The abundance of water is the main reason the Earth is

habitable


The polarity of water molecules results in hydrogen bonding

• Water is the only common substance that exist in the natural environment in all three physical states of matter: solid, liquid, and gas.


Properties of water• Water is such a good solvent because it is a polar

molecule • A molecule in which electrons are not shared

equally between atoms • What type of bonds shared electrons equally???• Partial negative charge at one end and a partial

positive charge at the other. • Water is classic example• H-O-H

Properties of water• Each water molecule has a partial

charge on each end, so it can form electrostatic attractions, known as hydrogen bonds, with one another and with other molecules.

Four emergent properties of water contribute to Earth’s fitness for life

• Four of water’s properties that facilitate an environment for life are:

– Cohesive behavior (clinging to itself)– Ability to moderate temperature– Expansion upon freezing– Versatility as a solvent


• Surface tension, a measure of the force necessary to stretch or break the surface of a liquid, is related to cohesion.– Measure of how hard it is to break the surface of a

liquid– Jumping in the pool (belly up)

• Surface tension is related to cohesion– Water has greater surface tension than most liquids– Invisible film– Some animals can walk or stand on water

Properties of water• Water is an excellent solvent for other polar

molecules and substances that contain ionic bonds

• Na+ CL-• Ionic bonds are strong bonds formed between

oppositely charged ions, salt (an atom that has an electrical charge resulting from the loss or gain of electrons).

Properties of water

• Water molecules can absorb a lot of energy before they get hot and vaporize (turn into a gas) because of their hydrogen bonds.

• Lakes, swimming pools are cool in summer• Ice floats because water is less dense as a

solid than as a liquid. – Ice cubes float– Expands when freezes (coke can)

Moderation of Temperature

• Water absorbs heat from warmer air and releases stored heat to cooler air

• Water can absorb or release a large amount of heat with only a slight change in its own temperature- effective heat bank


Properties of water• The different chemical properties of water-

based solutions reflect their pH –• The concentration of hydrogen ions (H+) in

a solution.• pH ranges from 0 to 14.

Properties of water• Water molecules (H2O) can split briefly into

separate hydrogen (H+) and hydroxide (OH-) ions. • In pure water, the number of separated H+ ions is

exactly equal to the number of separated OH- ions, and the pH is therefore 7, or neutral.

Properties of water• Acids have a higher

concentration of hydrogen ions (H+) and a pH closer to 0. When acids are added to water, they increase the concentration of hydrogen ions and make the solution more acidic.

• Acids are less than 7• Examples• Battery acid, orange juice,

coffee

Properties of water• Bases have a lower

concentration of hydrogen ions (H+) and a pH closer to 14.

• Bases remove H+ ions from a solution, thereby increasing the proportion of OH- ions.

• Bases are more than 7• Baking soda, ammonia

Properties of water

• Strong acids and strong bases are highly reactive with other substances, which makes them destructive to the molecules in a cell. – Many biochemical reactions take place only at a

certain pH. Human pH 7.35-7.4, can die at 7 or 8

• Living things are extremely sensitive to changes in pH, and most function best when their pH stays within a specific range.

Weird Life

• NASA– Carbon based molecules and cells

• Some things that bind rules of life• Viruses

– Reproduce and pass their genetic information to new viruses

– Not made of cells at all– Protein shell with DNA or RNA inside– Infect a host cell (human cell) use cellular machinery to

make copies of itself

Prions

• Noncellular and Self-replicating entity• Infectious proteins that cause mad cow

disease– Deterioration of the brain and spinal cord

• Are viruses and prions alive?• NASA should not just focus on water and

organic molecules for signs of life

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Chapter 2 What is life? Picture removed. First meteorite, ALH84001 Discovered by Roberta Score in...

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