life at the cellular level

Question 1

Describe the features of prokaryotic cells vs eukaryotic cells.

Answer 1

Prokaryotic cells: no nuclear membrane, no mitochondria and no membrane bound organelles. Eukaryotic cells: multicellular animals and plants, membrane bound organelles and nucleus.

Question 2

What does facilitated diffusion require?

Answer 2

Carrier molecules.

Question 3

What are the 4 types of junctions in cells?

Answer 3

1) Tight/occulding junctions - prevent extracellular constituents getting inside the cell. 2) Adhesive - link actin filaments of 2 different cells. 3) Desmosomes: link keratin filaments in 2 different cells. 4) Gap: channels linking 2 cell cytoplasms together for communication eg. heart muscle.

Question 4

What is the difference between pancrine and endocrine?

Answer 4

Pancrine: target cell is close to signalling cell. Endocrine: effects can be further away

Question 5

What type of DNA do mitochondria have?

Answer 5

Their own circular DNA. They self-replicate, have their own ribosomes and make most of their own proteins.

Question 6

What is the difference between heterochromatin and euchromatin?

Answer 6

Heterochromatin stains darker as it is tightly packaged and is in cells that are less active. Euchromatin is in cells that are active in transcription and stains lighter.

Question 7

What is the function of the smooth ER?

Answer 7

To break down compounds like drugs and glycogen or to synthesise compounds like lipids.

Question 8

What are the 3 molecules that make up the cytoskeleton?

Answer 8

Microfilaments (smallest, make up strands of actin), intermediate filaments (fibrous) and microtubules (long strands of alpha and beta tubulin).

Question 9

What is 99% of us made of and why?

Answer 9

H, N, O and C as they form the strongest bonds. C is the most versatile and forms the basis of all biomolecules.

Question 10

Define conformation and configuration.

Answer 10

Conformation: the arrangement of atoms in a molecule that can move without breaking H bonds. Configuration: fixed arrangement of atoms in a molecule.

Question 11

Give an example of alterations to cis and trans conformation.

Answer 11

Rhodopsin in the retina is made from retinal and opsin. Retinal is in cis conformation and light converts it to trans.

Question 12

Are biological molecules in L or D conformation?

Answer 12

All are in L.

Question 13

What are the 5 chemical reactions of life?

Answer 13

1) Redox: H transfered in glycolysis and NAD+ becomes NADH. 2) Making/breaking C-C bonds: cleavage of glucose in glycolysis to release some of its potential energy. 3) Internal rearrangements: G6P –> F6P. 4) Group transfers: F6P to F6bP. 5) Condensation and hydrolysis: molecules are joined by condensation and broken by hydrolysis. Condensation reactions make water and hydrolysis reactions use water to split compounds.

Question 14

How many bonds are in A-T vs C-G?

Answer 14

A-T has 2 bonds and C-G has 3 bonds.

Question 15

Describe the structure of glucose polymers.

Answer 15

Formed by condensation reactions between glucose monomers. Lots of monomers liked together? Locked in cyclic form except the end monomer which remains linear and forms a reducing end.

Question 16

What is the first law of thermodynamics?

Answer 16

Energy can be converted from 1 form to another, but the total energy in the universe remains constant.

Question 17

What is the second law of thermodynamics?

Answer 17

All energy changes ultimately lead to more disorder in the universe –> increase entropy.

Question 18

What does Gibbs free energy tell us?

Answer 18

How spontaneous a reaction is in a closed system. G = H- TS.

Question 19

When would a spontaneous reaction occur?

Answer 19

If delta G is negative.

Question 20

Why are some reactions coupled?

Answer 20

So that thermodynamically unfavourable reactions can occur. For example, glycolysis is overall delta G negative.

Question 21

Intermediates in reaction pathways are often said to be in?

Answer 21

Dynamic steady state. The intermediate molecule does not change in concentration even through it is being made and degraded.

Question 22

Define metabolism.

Answer 22

The chemical process in a living organism whereby food is used for tissue growth or reproduction.

Question 23

What does free energy flow in pathways depend on?

Answer 23

ATP hydrolysis and ADP condensation, ATP allows anabolic, thermodynamically unfavourable reactions to proceed through coupling of catabolic, thermodynamincally favourable reactions.

Question 24

What is the difference between a nucleotide and a nucleoside?

Answer 24

Nucleoside = Sugar + Base. Nucleotide = Sugar + Base + Phosphate.

Question 25

Describe the bonding in water.

Answer 25

Water is polar as O is more electronegative that H.

Question 26

What is a hydrogen bond?

Answer 26

A bond between any electronegative atom (O or N usually) and a H atom that is electropositive. These molecules are polar and soluble in water.

Question 27

What is the difference in water solubility between charged and uncharged molecules?

Answer 27

Charged molecules are water soluble. Un-charged molecules are hydrophobic.

Question 28

What is a liposome?

Answer 28

Water on the inside and outside.

Question 29

How are hydrophobic lipids transported through the blood?

Answer 29

In a chylomicron.

Question 30

pH + pOH = ?

Answer 30

14. 1 pH unit is a 10-fold increase/decrease in concentration of H ions.

Question 31

What is the difference between a stong and weak acid?

Answer 31

Strong acids fully dissociate in water. Weak acids only partially dissociate.

Question 32

What is a conjugate acid-base pair?

Answer 32

Acids are proton donors and bases are proton acceptors. A proton donor and a proton acceptor make up a conjugate acid-base pair.

Question 33

What is the dissociation constant?

Answer 33

The tendency for an acid to lose its proton and form its conjugate base.

Question 34

What happens when you make a solution of weak acid in pure water then add NaOH to change the pH?

Answer 34

Acetic acid ionises slightly. NaOH dissociates completely. The OH binds to the H of acetic acid to form water. As more NaOH is added, more HAc ionises to Ac. At the midpoint, 50% of NaOH is added. 50% of HAc is dissociated to give HAc and Ac. Here, pH = pKa. Beyond the midpoint, HAc continues to be used up until all of the original acid is ionised to Ac.

Question 35

What is pKa?

Answer 35

The pH value at which there are equal concentrations of the acid and conjugate base.

Question 36

When does full titration occur?

Answer 36

When all of the original HAc is ionised to Ac.

Question 37

What is a buffer?

Answer 37

A buffer solution is one which resists changes in pH when small quantities of an acid or an alkali are added to it. Buffering range is when lots of OH is added without a big change in pH.

Question 38

What is the Henderson-Hasselbalch equation used for?

Answer 38

Relates acid dissociation to buffering ability of weak acid/conjugate base. Use when you are trying to work out the amount of weak acid or conjugate base you have in a given biological system.

Question 39

What do buffers do in the body?

Answer 39

Mop up protons or dissociate if a solution is too alkaline. They maintain balance.

Question 40

Which 2 buffer systems are important in the body?

Answer 40

In cells - phosphate buffer system. In plasma - bicarbonate buffer system.