Biology Exam 1

Characteristics of a good hypothesis

• Testable

• Falsifiable

• Neither prove hypothesis is correct

Theory

• broader than hypothesis

• broad enough for new hypothesis

• Supported by large body of evidence

Science

• approach to understanding natural world

Inquiry

• search for info and exploration of natural phenomena

Controlled Experiment

• Compares experimental group w/ controlled group

• Variable → factor that is manipulated or measured

Independent var

• factor being manipulated

Dependent var

• factor being measured and affected by independet var.

Structure of an atom

• Proton (+1)

• Electron (-1)

• Neutron (0)

Element

• substance that can’t be broken down to other substance by chemical reaction

• made of one type of atom

Compound

• substance consiting of 2 or more diff elements in fixed ration

Atomic No

• shows # of protons elements contain

• Uncharged = sampe protons + electrons

Atomic Mass

avrg of all isotopes

PE of electrons

• more PE = further from nucleus

• Electrons only have avrg distances from nucleus

• Bc of only avrg distance → only certain potential energies

Electron Shells

• Electrons found in electron Shell

• lowest energy on first shell and highest on third

Electron orbital

• Each shell has one or more orbital

• Space where electron spends 90% of time

• Each orbital can have 2 max electrons

Paired electron

orbital has 2 electrons

Unpaired electron

orbital has 1 electron

Valance shells and valance elctrons

• Outer shell = valence shells

• Electons in valence shell = valence electrons

Completing Valence Shell

• complete by forming chemical bonds

• type of chem bond is diff for atom off diff elements

Covalent bond

• atoms complete valence shell by forming cov bonds

• The shairing of pair of valence electrons to form a molecule

Polar Covalent bonds

• When electrons are shared between atoms of different electonegativities more time is spent on more electronegative atom.

• More electro neg atom = partial neg charge

• Less electroneg atom = partial pos charge

Non polar covalent bonds

• Cov bones formed between atoms w/ approx equal electronegativities

• electros shared equally

Electronegativities of Elements

1. Oxygen

2. Nitrogen

3. Carbon ~ Hydrogen

Ionic bonds

• Atom transfers an electron to another atom

• gain atom = anion

• lose atom = cation

• Does not result in molecules as molecules are covalently bonded

Hydrogen can form ionic or covalent bonds?

True. They do this by giving or receiving electron

Hydrogen bonds

• form when hydrogen atom covalently bonds to electronegative atom is attracted to another electroneg atom

• much weaker than cov bond and ionic bond

• Can only form between molecules

Van der waals interactions

• electrons not evenly distributed causing regionds of partial neg and pos charges allowing atoms + molecules to come tg

• weakest chemical bond

Biology bond rankings

1. covalent bonds

2. Ionic bonds

3. Hydrogen bonds

4. Van der wall interactions

Chemical reactions

• are the making and breaking of chemical bonds

• Chemical reactions are reversible

Forwarde and reverse reactions

• occur at same rate and concentrations of products + reactants stop chaning

• does not mean equal concentrations

Structure of water

• Oxygen is electronegative cause electron to spend more time w/ oxygen

• As a result

  • Cov bonds in water are polar

  • Water is a polar molecule

  • Oxygen = partial neg | Hydrogen = parial pos

Solvent

• substances that are dissolving agents

Solutes

• substances that are getting dissolved

Why is water a great ion dissolver

• partial neg interactats with Na+ and partial pos interacts with Cl-

Avogadoro’s number

6.02 × 10²³

pH

• negative log of hydrogen ion (pH = -log[H+])

Dissociation of water molecules

• water molecules break part so the exist in equilibrium with hydronium ions [H3O+] and hydroxide ions (OH)

• 2 H2O =[H+] + [OH-]

Why does pure wate have a pH of 7

• [H+] and [OH-] are both equal at 10^-7

Acids

• Acids that increase H3O+ concentration

• Do this because H3O+ comine with OH- ions

• This forms new water molecules decreasing [OH-]

Bases

• substances that decrease H3O+ concentration

• Do this by realeasing OH- in water

• Or Accept H+ (NH₃ + H₂O ⇌ NH₄⁺ + OH⁻)

Calculating PH

[H+] x [OH-] = 10-14M at 25C

Carbon’s 4 covalent bonds

1. Carbon has 4 valence electrons but needs 8 to be stable, so it forms 4 bonds.

2. To make 4 bonds, one of carbon's 2s electrons jumps up to the empty 2p orbital, leaving 4 unpaired electrons.

3. Those 4 orbitals blend together into 4 identical sp³ orbitals, each ready to form a bond. Making the bonds releases more energy than the jump cost. (tetrahedral shape)

Examples of carbon-based molecules

• Methane (CH4)

• Ethane (C2H6)

• Ethene (C2H4)

Isomers

• molecules with have same molecular formula but different 3D structures

3 types of Isomers

1. Structural Isomers

2. Cis-Trans Isomers

3. Enantiomers

Structural isomers

molecules with same molecular formula but a different arrangement of atoms (different connectivity)

Cis-Trans Isomers (non-structural)

• molecules that vary in arrangement of atoms around double bond

• Ex:

  • cis-2-butene: both CH₃ groups on the same side

  • trans-2-butene: CH₃ groups on opposite sides

Enatiomers

molecules that are mirror image of each other

Asymetric carbon

• central caron of enantiomer

Hydrocarbons

• consist of carbon and hydrogen

• are hyrophobic and contain lots of energy

Hydrocarbonds are hydrophobic because:

C-H bonds are nonpolar so they cant form hydrogen bonds

Functional group

• chemical groups that affect shape and function of molecule by direct involment in chemical reactions

• molecules are categorized by functional groups

Hydroxyl group

• consist of oxygen covalently bonded to hydrogen

• polar and help form H-bonds to dissolve compounds

• can be organic alcholos like ethanol

Carbonyl group

• oxygen atom that shares double cov-bond with carbon atom

• polar because oxygen is more elctroneg than carbon

Aldehydes

Carbonyl groups that occur at end of chain

Ketones

Carbonyl groups that occur at middle of chain

Carboxyl group

• consist of carbon atom that share double cov bond with oxygen and single cov bond with OH bond

Amino Acid

• consist of nitrogen atom cov-bonded to hydrogen atoms

• Often bind H+ so can act as bases

Amines

molecules containing amine group

Sulfhydrl group

• contain sulfur atom cov-bonded to hydrogen atom

• 2 sulfhydrl groups can form cov binds heping stabilize protein structures

Phosphate group

• phosphorus atom cov bonded to four oxygen atoms

• Carry negative charge

• Carry lots of energy so p-groups raise energy levels of molecules containing them

Thiols

molecules containing sulfhydrl groups

Organic Phosphates

• molecules containing phosphate groups

Methyl Group

• Carbon cov-bonded to 3 hydrogen atoms

• Adding methyl groups affects activity levels of nearby genes

Methylated

• molecules containing methyl group

Carbohydrates

• include sugars and polymers of sugar

• are organic molecules made of carbon, hydrogen, and oxygen

Sugars

• are polyhydroxy, aldehydes, or ketones

• Sugars have carbonyl group (aldehyde or ketone)

• Usually end in “Ose”

Hydroxyl and carbonyl

• are polar so sugars dissolve in water

Monosaccharides

• simplest sugar

• Usualy have formula (CH2O)n n=3 to 7

Aldoses

• monosaccharides that have aldehyde group

Ketoses

• monosaccharides that have ketose group

Function of monosaccharides

• Energy source

• used as building blocks to make larger molecules

Dissacharides

• 2 monosaccharides joined by cov bond

• Joined together by dehydration reaction

Dehydration Reaction

• type of condesation reaction that releases water molecule

glycosidic linkages

• bonds between monosaccharides

Polymers

• Large molecule made of repeating monomers

Monomers

• repeating units that form polymers

Polysaccharide function

• are either storage polysaccharides (carbs) or structural polysaccharides

Storage polysaccahrides

• function as surce of energy (ex: starch and glycogen)

Startch

• polymer of glucose.

• Made by plants store in chloroplasts

Glycogen

• polymer of glucose

• Stored in liver and muscle cells

Glycogen and starch

• broken down by enzymes into glucose

• done through hydrolysis reaction

• The glucose can befurther metabolized to produce energy or building blocks

Structural polysaccharides

• help form cellur and extracellular structures (ex: celluose)

Cellulose

• form much of cell wall surrounding plant cel

• make plant tissue rigid

• major component of wood

alpha glucose monomers

starch and glycogen

beta glucose monomers

Cellulose

Cellulose cant be digested because

because of its chemical structure and the enzymes we lack.

Lipids

• molecules that dissolve partly in water

• NOT POLYMERS

Fats

• synthesized by dehydration reaction that joins fatty acids to glycerol by ester linkage

Triglycerides

• 3 fatty acids + 1 glycerol molecule

• Fatty acids vary in chain length and number of double bonds

• split by hydrolisys

Saturated fatty caid

• a fatty acid whose hydrocarbon chain has no C=C double bonds

Unsaturated fats

• have C=C double bonds

• less likely to solidify as double bonds lower melting temperature

Phospholipids

• have only 2 fatty acid chains attached to glycerol

• 3 pos is occupied to phosphate, which is negatively charged

• other groups can attach to phosphate

• Phosphate region is polar glycerol region is nonpolar

Function of phospholipids

• the main structural molecules of cell membranes, and their function comes from being amphipathic: part of the molecule loves water and part avoids it.

Membranes with unsaturated hydrocarbons are more

• fluid

• tails are kinked not allowing tight packing

Sterols

• have carbon skeleton with 4 fused rings

• Considered lipds bc theyre hydrophobic

• can function as steroid hormones

• or example cholestrol → important to cell memberanes

Proteins

• are polymers of amino acids, linked in a chain by peptide bonds.

Amino Acids structure

• 20 different amino acids

• R group usually below carbon varies

Polypeptides

• chain of many amino acids

• joined together by dehydration reaction

• results in peptide bond that forms protein

4 levels of protein structure

1. Primary structure

2. Secondary structure

3. Tertiary Structure

4. Quaternary Structure