Chap 3 - Biological Molecules Flashcards
Describe the structure of a water molecule
- two hydrogen atoms bonded covalently to an oxygen atom
- the covalent bond is polar - oxygen is slightly -tive and the hydrogen atoms are slightly +tive
What is the bond that links two water molecules together?
hydrogen bond
Explain what a hydrogen bond is and what molecules it can join
electromagnetic attraction between partially positively charged hydrogen atoms attached to a highly electronegative atom (oxygen, nitrogen)
Explain how a H bond links water molecules together
slight positive charge of a hydrogen atom of one molecule is attracted to the slight negative charge of an adjacent oxygen atom from another molecule
What are hydrogen bonds responsible for
holding together DNA, proteins, and other macromolecules.
Explain why water is polar
- oxygen and hydrogen atoms are bonded covalently - they share electrons
- oxygen has a larger positive nucleus, the electrons are shared unequally and they spend more time closer to it than the small nucleus of hydrogen which means the bond is polar
- causes the oxygen to become slightly negative because has greater share of negative electrons, meaning hydrogen is slightly positive (positive nucleus which has a smaller share of electrons)
Define electronegativity
the tendency of an atom or molecule to draw electrons towards itself.
Define dipole
a bond or molecule whose ends have opposite charges.
List the 5 roles that water plays in life
- solvent - most biological reactions happen in aqueous solution (cell cytoplasm is mainly water)
- reactant - hydrolysis, condensation
- transport medium - in blood, lymphatic system, excretory system, digestive system, vascular tissues, etc
- coolant - helps buffer temperature changes during chemical reactions in cells
- insulating layer - ice freezes and floats which insulates the water so seas do not freeze solid, providing aquatic organisms with a constant environment
Explain why the polar nature of water allows it to be a useful solvent
- excellent solvent for ions & polar molecules
- water mols are attracted to them, collect around them and separate them
- chemicals are then free to react with other chemicals in the solution
Explain why water cannot dissolve lipids & why that is useful
- because water molecules are attracted to each other, so push the non-polar molecules together.
- important to maintain stability of membrane structures which are mainly made of lipid molecules - water does not dissolve them
Explain why the polar nature of water allows it to be a useful transport medium.
- hydrogen bonds allow for thermal stability - remains a liquid over a big range of temperatures
- cohesion between water molecules means that when water is transported through the body, molecules stick together (hydrogen bonds between water molecules)
- cohesion and adhesion allow for capillary action
Explain why the polar nature of water allows it to be a useful coolant.
- because of its high thermal stability (high specific heat capacity) meaning it requires a lot of heat gain or loss to change its temperature
- tt also has a high latent heat of vaporisation (large amount of energy is needed to convert liquid water into gas)
- hydrogen bonding holds water molecules together, it takes a lot of energy to overcome them in order to release the particles and cause water to melt/evaporate
Explain why the polar nature of water allows it to be a useful reactant.
- in hydrolysis it is able to split up polymers or join them together by being removed from them
- this is due to the partial positive charge on the hydrogens, one of them splits away from the OH and binds to one part of the polymer while the OH binds to the other part
Why is water a good habitat?
- high thermal stability due to the hydrogen bonds helps keep the temperature stable - good environment for life
- because ice is less dense than liquid water, it floats forming an insulating layer - prevents seas from freezing
Why does ice float on water?
- as water cools down, the kinetic energy the molecules have gets reduced - they move less and therefore take up less space
- above 4*C, interactions between molecules are short, hydrogen bonds keep forming and breaking quickly
- below 4*C, the energy of water molecules falls below the energy of hydrogen bonds - they form much more frequently than they break
- this causes a lattice to be formed where the molecules are more spread out than in liquid water - less dense than disordered liquid water therefore it floats
Define hydrophillic
substance attracted to water
- water can dissolve them, tend to be polar molecules/ions
Define hydrophobic
substance that repels water
- water cannot dissolve them, tend to be non-polar molecules
Define cohesion
the ability of a substance to stick to a like substance
Define adhesion
the ability of a substance to stick to an unlike substance
List 3 examples of how water is used by prokaryotes and eukaryotes
- cytoplasm is made up primarily from water - where most metabolic reactions happen
- water being a solvent allows for molecules/ions to flow freely in the cytoplasm allowing for movement of substances in/out of cells
- supports plant cells thanks to turgor - water pressure inside of plant cells
List 6 examples of how water is used in plants, animals and fungi
- in animals with sweat glands - secrete sweat (made up of water
- hydrostatic skeleton - octopuses, snails which is made up of water-filled tubes which can expand and contract but pushing water in/out
- synovial fluid - in joints mostly made up of water, acts as lubricant in the joint
- circulatory system - blood is mostly water which allows animals to transport substances inside the organism
- xylem and phloem - thanks to capillary action, nutrients can be transported against the force of Gravity up to the top of the plant
- seminal fluid in animals - acts as a medium for the sperm cells to swim to the egg
Explain how water is used in unicellular and multicellular organisms
water is used by all organisms for hydrolysis and condensation of polymers
Explain why water can dome above the level of the glass container it is in? Explain the shape it makes.
- glass is made up of polar molecules to which water molecules are attracted to (hydrophilic) - adhesion
- while the water is in the container, some molecules touch glass which is above the level of water and they stick to it - adhesion
- other molecules stick to that molecule due to cohesion and stay like that while the original molecule is stuck to the glass, resulting in a concave meniscus shape