Transcript 추가3

Chapter 3
Water: The Matrix of Life
Overview





Section 3.1: Molecular Structure of Water
Section 3.2: Noncovalent Bonding
Section 3.3: Thermal Properties of Water
Section 3.4: Solvent Properties of Water
Section 3.5: Ionization of Water
3.1 물의 분자구조
-산소원자가 sp3혼성으로 사면체 기하학구조(그림3.1)
-산소의 전기음성도가 더 커 전자를 자기;쪽으로, 부분적인 음전하 (그림3.2)
극성(전자의 분포가 비대칭)
-물분자는 구부러져 104.50 (그림3.3)
-전하가 분리된 쌍극자여서 전기장에서 반대방향(그림3.4)
-수소결합: 극성 분자사이의 정전기적 상호작용(그림3.5)
Section 3.1: Molecular Structure of Water
Water is essential for life
Water’s important properties include:
Chemical stability
Remarkable solvent properties
Role as a biochemical reactant
Hydration
Section 3.1: Molecular Structure of Water
Water has a tetrahedral
geometry
Oxygen is more electronegative
than hydrogen
Figure 3.1 Tetrahedral
Structure of Water
Section 3.1: Molecular Structure of Water
Larger oxygen atom has partial negative charge
(d-) and hydrogen atoms have partial positive
charges (d+)
Figure 3.2 Charges on a Water Molecule
Figure 3.3 Water Molecule
Section 3.1: Molecular Structure of Water
Bond between oxygen and hydrogen is polar
Water is a dipole because the positive and
negative charges are separate
Figure 3.4 Molecular
Dipoles in an Electric
Field
Section 3.1: Molecular Structure of Water
An electron-deficient hydrogen
of one water is attracted to the
unshared electrons of water
forming a hydrogen bond
Can occur with oxygen,
nitrogen, and fluorine
Has electrostatic (i.e., opposite
charges) and covalent (i.e.,
electron sharing) characteristics
Figure 3.5 Hydrogen Bond
3.2 비공유결합
-약한 결합(표3.1)
-생체분자의구조와 기능에 영향줌
(1)이온화 상호작용
-상반된 전하를 띤 원자나 화합그룹사이
-NaCl,
-양전하, 음전하 아미노산곁사슬의 인력을 염다리 혹은 반발력: 단백질접힘,
효소작용, 분자인식 등
(2)수소결합
-수소와 산소, 질소 또는 유황사이의 공유결합은 매우 극성이어, 수소원자가
인접된 O, N, S에 약하게 끌림(그림3.6)
-물은 3차원적으로 집합체를 이룸; 높은 끓는점, 녹는점, 기화열
Section 3.2: Noncovalent Bonding
Noncovalent interactions are electrostatic
Weak individually, but play vital role in biomolecules
because of cumulative effects
Section 3.2: Noncovalent Bonding
Three most important noncolvalent bonds:
Ionic interactions
Van der Waals forces
Hydrogen bonds
Section 3.2: Noncovalent Bonding
Ionic Interactions
Oppositely charged ions attract one another
Ionized amino acid side chains can form salt bridges
with one another
Biochemistry primarily investigates the interaction
of charged groups on molecules, which differs from
ionic interactions like those of ionic compounds (e.g.,
NaCl)
Section 3.2: Noncovalent Bonding
Hydrogen Bonds
Electron-deficient hydrogen is
weakly attracted to unshared
electrons of another oxygen or
nitrogen
Large numbers of hydrogen
bonds lead to extended network
Figure 3.6 Tetrahedral
Aggregate of Water
Molecules
(3)반데르발스힘
-일시적인 정전기적 상호작용,
-영구적이거나 일시적으로 유도된 쌍극자사이에 일어남
-거리에 따라 인력 혹은 반발력, 반데르발스 반경에서 가장 큼
-3가지 형태
1. 쌍극자-쌍극자 상호작용: 수소결합이 이의 한 형태(그림3.7a)
2. 쌍극자-유도된 쌍극자 상호작용
-영구적인 쌍극자는 인접한 분자의 전자분포를 뒤틀리게하여 일시적인
쌍극자형성을 유도한다(그림3.7b)
3. 유도된 쌍극자-유도된 쌍극자(그림3.7c)
-인접된 무극성분자 내 전자이동은 인접분자 내에 일시적인 분자불균형을
초래한다.
-런던 분산력:DNA분자 내 위아래 염기고리의 상호작용
Section 3.2: Noncovalent Bonding
Van der Waals Forces
Occur between neutral,
permanent, and/or induced
dipoles
Three types:
Dipole-dipole interactions
Dipole-induced dipole
interactions
Induced dipole-induced
dipole interactions
Figure 3.7 Dipolar Interactions
3.3 물의 성질
-녹는점 끓는점이 높다(표3.2); 수소결합
-물 한 분자는 4개의 수소결합(그림3.8)
-물 온도를 증가시키는데 에너지가 높다(표3.3)
-물은 높은 기화열과 열용량
3.4 물의 용매성질
-이온, 당, 많은 아미노산 등을 녹인다
1)친수성
-용매화 구형(그림3.9)
구조화된 물 (그림3.10)
졸-겔(그림3.11): 아메바의 위족, G-actin F-actin의 가역적중합반응
2)소수성분자
-물의 용매화망상에서 배제되어 작은 방울로 뭉친다
-물이 무극성분자 주위에 새장모양(그림3.12)
-무극성물질사이의 인력: 소수성 상호작용
3) 양극성
-극성그룹과 무극성그룹을 포함
-예: 이온화 지방산(카르복실기와 탄화수소, 미셀형성 그림3.11)
Section 3.3: Thermal Properties of Water
Water’s melting and boiling points are
exceptionally high due to hydrogen bonding
Each water molecule can form four hydrogen bonds
with other water molecules
Extended network of hydrogen bonds
Section 3.3: Thermal Properties of Water
Figure 3.8 Hydrogen Bonding
Between Water Molecules in Ice
Maximum number of hydrogen bonds form when
water has frozen into ice
Open, less-dense structure
Section 3.3: Thermal Properties of Water
Water has an exceptionally high heat of fusion and
heat of vaporization
Helps to maintain an organism’s internal
temperature
Section 3.4: Solvent Properties of Water
Figure 3.9 Solvation
Spheres
Water is the ideal biological solvent
Hydrophilic Molecules, Cell Water Structuring, and
Sol-Gel Transitions
Water can dissolve ionic and polar substances
Shells of water molecules form around ions forming
solvation spheres
Section 3.4: Solvent Properties of Water
Figure 3.10 Diagrammatic
View of Structured Water
Structured Water
Water is rarely free
flowing
Water is associated
with macromolecules
and other cellular
components
Forms complex threedimensional bridges
between cellular
components
Section 3.4: Solvent Properties of Water
Figure 3.11 Amoeboid
Movement
Sol-Gel Transitions
Cytoplasm has properties of a gel (colloidal
mixture)
Transition from gel to sol important in cell
movement
Amoeboid motion provides an example of
regulated, cellular, sol-gel transitions
Section 3.4: Solvent Properties of Water
Figure 3.12 The
Hydrophobic Effect
Hydrophobic Molecules and the Hydrophobic Effect
Small amounts of nonpolar substances are excluded
from the solvation network forming droplets
This hydrophobic effect results from the solvent
properties of the water and is stabilized by van der
Waals interactions
Section 3.4: Solvent Properties of Water
Amphipathic Molecules
Contain both polar and
nonpolar groups
Amphipathic molecules
form micelles when mixed
with water
Important feature for
the formation of
cellular compartments
Figure 3.13 Formation of Micelles
(4)삼투압
-반투막에의 물의 통과현상 (그림3.14)
-삼투압은 용질농도에 의존(그림3.15)
-삼투압=iMRT (i=용질의 이온화정도, M=몰랄농도)
-예: 0.1M NaCl의 I 값? (82페이지)
-저장,등장, 고장액(그림3.16)
-막전위; 세포막표면상의 이온의 불균형으로 전기전도, 능동수송, 수동수송
-삼투압의 조절, 식물은 팽압
-리포트?(문제3.2 - 3.4)
Section 3.4: Solvent Properties of Water
Figure 3.14 Osmotic
Pressure
Osmotic Pressure
Osmosis is the spontaneous passage of solvent
molecules through a semipermeable membrane
Osmotic pressure is the pressure required to stop
the net flow of water across the membrane
Osmotic pressure depends on solute concentration
Section 3.4: Solvent Properties of Water
Can be measured with an osmometer
or calculated ( =iMRT)
Cells may gain or lose water because
of the environmental solute
concentration
Solute concentration differences
between the cell and the environment
can have important consequences
Isotonic solution
Hypotonic solution
Hypertonic solution
Figure 3.16 Effect of Solute Concentration on Animal Cells
Section 3.4: Solvent Properties of Water
Proteins with ionizable amino acid side chains affect
cellular osmolarity by attracting ions of opposite
charge
There is asymmetry of charge across the membrane
due to ions forming an electrical gradient (membrane
potential)
Unlike animal cells, plant cells use osmotic pressure
to drive growth via turgor pressure
3.5 물의 이온화
-물의 이온화
Keq, 평형상수
Keq x 55.5 은 이온적 Kw
pH=-log[H+]
(1)산, 염기 그리고 pH
-강산 강염기
-약산 약염기
약산과 이의 짝염기
Ka, 산의 해리상수(클수록 강산)
pKa= -logKa (pKa가 낮을수록 강산)(표 3.4)
- pH척도(그림3.17), 수소이온 농도의 음성로그: pH= -log[H+]
Section 3.5: Ionization of Water
Water can occasionally ionize, forming a hydrogen
ion (H+) and a hydroxide ion (OH-)
In an aqueous solution, a proton combines with a
water molecule to form H3O+ (hydronium ion)
H2O  H+ + OH- (reversible)
Section 3.5: Ionization of Water
The ion product of water is referred to as Keq[H2O]
or Kw = [H+][OH-]
Kw at 25°C and 1 atm pressure is 1.0  10-14
Kw is temperature-dependent; therefore, pH is
temperature-dependent as well
Section 3.5: Ionization of Water
Acids, Bases, and pH
An acid is a proton donor
A base is a proton acceptor
Most organic molecules that donate or accept
protons are weak acids or weak bases
A deprotonated product of a dissociation reaction
is a conjugate base
Section 3.5: Ionization of Water
The pH scale can be used to
measure hydrogen ion
concentration
pH=-log[H+]
Figure 3.17 The pH Scale and the pH Values of
Common Fluids
Section 3.5: Ionization of Water
pKa is used to express the
strength of a weak acid
Lower pKa equals a stronger
acid
pKa=-logKa
Ka is the acid dissociation
constant
Figure 3.17 The pH Scale and the pH Values of
Common Fluids
Section 3.5: Ionization of Water
(2) 완충액
-산독증, 알칼리혈증
-완충액
-르샤트리에르의 원리: 평형상태에서 한 반응에 어떤 변화를 주면 그 변화를
제거하는 방향으로 평형이 일어난다.
-예: 아세트산과 아세트산염나트륨으로 구성된 아세트산염완충액(그림3.18)
•완충용량(buffer capacity)
-완충액성분의 농도에 비례
•Henderson-Hasselbalch방정식
-HA= H+ + A-pH=pKa + log[A-]/[HA]
-[A-]=[HA]이면, pH=pKa (그림3.18)
-가장 효과적인 완충액은 pKa값 위아래 1pH범위
-리포트?, 문제3.5-3.11
Section 3.5: Ionization of Water
Buffers
Regulation of pH is universal and essential for all
living things
Certain diseases can cause changes in pH that can
be disastrous
Acidosis and Alkalosis
Buffers help maintain a relatively constant
hydrogen ion concentration
Commonly composed of a weak acid and its
conjugate base
Section 3.5: Ionization of Water
Buffers Continued
Establishes an
equilibrium between
buffer’s components
Follows Le Chatelier’s
principle
Equilibrium shifts in
the direction that
relieves the stress
Figure 3.18 Titration of Acetic Acid
with NaOH
Section 3.5: Ionization of Water
Henderson-Hasselbalch Equation
Establishes the relationship between pH and pKa for
selecting a buffer
Buffers are most effective when they are composed of
equal parts weak acid and conjugate base
Best buffering occurs 1 pH unit above and below the
pKa
Henderson-Hasselbalch Equation
pH = pKa + log
[A-]
[HA]
Section 3.5: Ionization of Water
Worked Problem 3.5 (Page 91)
Calculate the pH of a mixture of 0.25 M acetic acid
(CH3COOH) and 0.1 M sodium acetate (NaC2H3O2)
The pKa of acetic acid is 4.76
Solution:
pH = pKa + log
pH = 4.76 + log
[acetate]
[acetic acid]
[0.1]
[0.25]
= 4.76 + 0.398 = 4.36
*한 개 이상의 이온화그룹을 갖는 약산
-인산(phosphoric acid, H3PO4), 약한 다양성자 산
-NaOH로 적정(그림3.19), 단계적 이온화
-가장 산성 그룹의 pKa를 pK1으로 표기
-낮은 pH에서 대부분 분자들이 양성자화된다
-pH와 pK1이 동일할 때 H3PO4와 H2PO4-의 양이 동일함
-아미노산의 이온화: 두 기능기, 적정시 –COOH가 먼저 양성자를 잃고 다음으로 –
NH3가 다음으로
Section 3.5: Ionization of Water
Figure 3.19 Titration of
Phosphoric Acid with
NaOH
Weak Acids with Multiple Ionizable Groups
Each ionizable group can have its own pKa
Protons are released in a stepwise fashion
(3)생리적인 완충액
•중탄산염완충액
CO2 + H2O ↔ H2CO3, Carbonic acid
H2CO3 ↔ H+ + HCO3-, Bicarbonate
CO2 + H2O ↔ H++ HCO3-, 실제 혈액내
•인산완충액
-H2PO4-(인산이수소)= H+ + HPO42+ (인산수소)
*단백질완충액
-곁사슬의 이온화기
-농도가 많음, 헤모글로빈 알부민 등
*세포의 부피조절과 물질대사 (그림3A)
삼투몰 농도의 작은 변화를 보정하는 기작: 막을 통한 무기이온의 교환
-단백질합성 시: 아미노산 감소로 물 유출, 무기이온의 이입
-단백질분해 시; 반대
-삼투질이라는 다량의 삼투활성물질의 합성: 스트레스를 받으면 다량의
알코올(소비톨 등), 아미노산, 타우린(아미노산유도체)를 만듦
Section 3.5: Ionization of Water
Physiological Buffers
Buffers adapted to solve specific physiological
problems within the body
Bicarbonate Buffer
One of the most important buffers in the blood
CO2 + H2O  H+ + HCO3- (HCO3- is bicarbonate):
This is a reversible reaction
Carbonic anhydrase is the enzyme responsible
Section 3.5: Ionization of Water
Phosphate Buffer
Consists of H2PO4-/HPO42(weak acid/conjugate base)
H2PO4-  H+ + HPO42Important buffer for
intracellular fluids
Protein Buffer
Proteins are a significant
source of buffering capacity
(e.g., hemoglobin)
Figure 3.20 Titration of
H2PO4- by Strong Base