Life at the Cellular Level Flashcards
1
Q
Prokaryotic cells
A
Bacteria
Lack Nuclear membrane
No Mitochondria
No membrane bound structures
2
Q
Eukaryotic cell
A
Human cells
Multicellular animals and plants
Nucleus with membrane
Membrane bound structures
3
Q
Stem Cells
A
Cells that can differentiate into many cell types – multipotent
Or all cell types of the body – pluripotent
4
Q
Cell Differentiation
A
Changes in gene expression is reflected in the alteration of cell structure and behaviour
Cell fusion – Small number of cell types undergo a process of cell fusion as a part of their normal differentiation
5
Q
Cancer cells
A
- Divide with out any control
- Fail to coordinate with normal cells
- Fail to differentiate into specialised cells
- Displace and replace the normal cells – If not stopped
In normal cell division, damaged cells undergo apoptosis
6
Q
Tissue Remodelling – Apoptosis
A
- Is a process of programmed cell death
- Is a central mechanism controlling multicellular development
- Apoptosis and cell proliferation (increase of the number of cells) are intimately coupled
7
Q
Tissues
A
Functional arrangements of cells Types of tissues: 1) Epithelial 2) Connective 3) Nervous 4) Muscular
8
Q
Organs
A
Mixture of different tissues
9
Q
Systems
A
Cells or organs with similar functional roles
10
Q
Cell membrane
A
- Selective barrier
- Detects chemical messengers and signalling molecules from surrounding cells or other organs
- Membrane lipids are amphipathic (hydrophilic head and hydrophobic tail)
- Membrane proteins (some span the membrane, others are embedded in the membrane)
11
Q
Passive diffusion
A
- Concentration gradient needed
- Lipid-soluble molecules pass freely (non-polar) through lipid bilayer
12
Q
Facilitated diffusion
A
- Concentration gradient needed
- Requires carrier molecules which can be specific (eg- glucose) or non-specific
13
Q
Tight Junction (Occluding Junction)
A
- Seals gap between epithelial cells
- Create a physical barrier to diffusion across layers of cells
- Dependent on calcium
Examples:
Intestine
Kidney
Blood brain barrier
14
Q
Adhesive Junctions
A
Adherens junctions:
- Link actin filaments in two different cells
Desmosomes:
- Link Keratin filaments in two different cells
15
Q
Gap Junctions
A
- Channels linking two cell cytoplasm together that allows passage of small water-soluble molecules.
Examples:
Heart muscle
Liver
Pancreas
Connexins:
6 subunit membrane spanning proteins
16
Q
actin-linked cell-matrix adhesion
A
anchors actin filaments in cell to extracellular matrix
17
Q
Hemidesmosome
A
anchors intermediate filaments in a cell to extracellular matrix
18
Q
Cell signalling can be:
A
- Contact dependant (membrane-bound signal molecule)
- Paracrine (local mediator)
- Synaptic (neurotransmitter)
- Endocrine (hormone)
19
Q
Mitochondria
A
- Outer membrane contains pores (porin protein)
- Inner membrane has cristae
- Matrix contains binding sites for calcium and also most of the enzymes for oxidation of food molecules (e.g. Krebs cycle)
20
Q
Mitochondria also have:
A
- Their own circular DNA
- Ribosomes – similar to bacterial ribosomes
- Synthesise most of their own proteins
- Self-replicate
21
Q
Nucleus
A
- Contains DNA, nucleoprotein and some RNA
- Nucleoli are sites of ribosomal RNA synthesis and ribosomal assembly
DNA tends to be one of two forms:
- Heterochromatin
- Euchromatin
22
Q
Nuclear Membrane (Envelope)
A
- Phospholipid bilayer
- Encloses the nucleus
- Contains pores
- Closely associated with the endoplasmic reticulum
23
Q
Endoplasmic Reticulum and Golgi Apparatus
A
- Membrane bound
- Rough ER has ribosomes attached
- Protein modifications and transport coordinated by the RER and Golgi
- Smooth ER used mainly to breakdown compounds (e.g. drugs and glycogen) or synthesise some compounds (e.g. lipids)
24
Q
Lysosomes
A
- Used to separate enzymes from the rest of the cell
- Used in autophagy (digestion of cells own materials) or digestion of engulfed particles (e.g. bacteria)
25
Cytoskeleton
- Supports and maintains cell shape
- Holds organelles in position
- Moves organelles
- Involved in cytoplasmic streaming
- Interacts with extracellular structures to hold cell in place
26
Cell Surface Projections
Cilia and eukaryotic flagella are made of microtubules
Cilia—short, usually many present, move with stiff power stroke and flexible recovery stroke
Flagella—longer, usually one or two present, movement is snakelike
27
Microfilaments
Made up of strands of the protein actin; often interact with strands of other proteins
28
Intermediate Filaments
Made up of fibrous proteins organised into tough, ropelike assemblages that stabilise a cell's structure and help maintain its shape
29
Microtubules
Long, hollow cylanders made up of many molecules of the protein tubulin.
Tubulin consists of two subunits:
- alpha tubulin
- beta tubulin
30
10 natural elements that are structural parts of organisms.
we need grams of these in our diets daily.
| H, C, N, O, Na, P, S, Cl, K, Ca
31
most versatile
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Carbon
It can form stable:
- Single bonds (with H)
- Single and double bonds (with O and N)
- Single, double and sometimes triple bonds with other C atoms
```
32
99% of you is
H, O, N and C as light atoms form the strongest bonds
| These four are the lightest atoms that can make 1, 2, 3 and 4 bonds respectively
33
Polarity of C bonds is critical to functionality.
| C-C and C-H are...
relatively stable as they share e-’s equally.
34
Polarity of C bonds is critical to functionality.
| C-O and C-N, or C-functional group bonds are...
highly polar, which alters the C bond reactivity
35
Configuration
The fixed arrangement of atoms in a molecule
36
Lots of biomolecules contain C=C, which is...
a rigid conformation
Can therefore only have two distinct configurations:
- Trans (C is on opposite sides)
- Cis (C is on same side)
Can only interconvert between the two by breaking and re-forming bonds
37
Chiral centre =
chiral C = asymmetric C
38
Two forms of chiral C
- L- and D-
- Laevo (left handed)
- Dextro (right handed)
39
Only way can rotate is to
break and re-form bonds.
As with retinal this configuration difference is important biologically.
All proteins are made from L-amino acids only
40
Conformation
The precise arrangement of atoms in a molecule.
41
Bonds that can rotate
allow many different conformations, which are inter-convertable without breaking and re-forming covalent bonds.
Lots of biomolecules contain C-C, which can rotate freely
42
In conformation, interactions of groups around the C-C bond
will dictate how freely the bond can rotate, which will favour certain conformations in the molecule
43
Chemical reactions of life
- Redox reactions
- Making and breaking C-C bonds
- Internal rearrangements
- Group transfers
- Condensation and hydrolysis reactions
44
reducing agent gets
oxidised as it loses electrons
45
oxidising agent is
reduced as it gains electrons
46
In many biological redox reactions
two e-’s (and two protons) are gained or lost
Often 2 hydrogen atoms are transferred from one molecule to another in dehydrogenation reactions.
eg- when glucose is turned into 2 pyruvate it needs 2NAD+ to be reduced into 2NADH. This gets oxidised back into 2NAD+ when 2 pyruvate is formed into 2 lactate.
47
Internal rearrangements example
In glycolysis, a rearrangement occurs before the sugar is split where Glucose 6-phosphate turns into Fructose 6-phosphate.
48
Group transfers example
In glycolysis, phosphate group is transferred where ATP provides energy
49
Condensations and hydrolyses
The sub-units of proteins, polysaccharides and nucleic acids are all joined by condensation and broken by hydrolysis reactions
50
Proteins
They are polymers of amino acid monomers linked by peptide bonds.
51
Cytoplasm
| three types of filaments that make up the cytoskeleton:
- microtubule (the largest),
- intermediate filament (the knobbly one)
- two actin filaments (the smallest ones)
ribosomes and proteosomes can be seen near these as well
52
Nucleic acids
polymers of nucleotide monomers linked by 3’,5’-phosphodiester bonds
53
Base in nucleic acids
- Pyrimidines (flat, single rings) – cytosine (C), thymine (T) and uracil (U)
- Purines (flat, double rings) – adenine (A) and guanine (G)
Flat planar structure of bases allows DNA to form the double helix
54
Polysaccharides
polymers of sugar monomers linked by glycosidic bonds
| e.g. Starch and glycogen
55
D-glucose is termed a reducing sugar as
The linear form (but not cyclic form) has an aldehyde group, which can be oxidised
If this is oxidised then the other reactant would be reduced, so glucose is termed a ‘reducing sugar’
56
aldehyde group
H
|
C = O
57
Glucose polymers
```
Formed by condensation reaction between two glucose monomers.
In glycogen (and starch), one glucose monomer is linked to another which locks the additional glucose in the cyclic form.
```
58
When lots of monomers link together, all monomers of the chain are
locked in the cyclic form except the end monomer, which can remain linear
This end monomer therefore forms a ‘reducing end’
59
Lipids
Usually contain one or more long-chain fatty acid that is saturated or unsaturated.
60
Several classes of lipid include
- Triacylglycerides
| - Phospholipids
61
Triacylglycerides
- Also called triglycerides
- Storage lipids
- Non-polar
- 3 fatty acid chains linked to glycerol
62
Phospholipids
- Similar to triglycerides,
- But they have a ‘head’ group attached to the glycerol
- This makes them polar
63
main types of energy
- heat
- light
- mechanical
- electrical
64
Laws that Govern Energy Changes
Energy can be converted from one form to another but the total energy of the universe remains constant
All energy transformations ultimately lead to more disorder in the universe, i.e. increase the entropy.
65
entropy increases when
usable energy decreases and unusable energy increases.
Entropy is also a gauge of randomness or chaos within a closed system. As usable energy is irretrievably lost, disorganisation, randomness and chaos increase.
66
entropy and cells
Cells use energy to grow and form complex molecules and systems
However, cells do not live in isolation – they are open systems, taking energy from the sun or food molecules to generate the order required for life.
The chemical reactions that generate the cell’s order produce heat, which is discharged into the surrounding environment and disorders it, so the total entropy increases (as the 2nd Law states).
67
“useful”, or Free energy in a closed system can be defined by 3 quantities:
- Enthalpy, H – heat released to surroundings (reflects number/kind of bonds formed/broken)
- Entropy, S –randomness/disorder
- Absolute temperature, T
68
Free energy change can be used to define the spontaneity of a reaction.
Spontaneous reactions can occur if a system:
- Gives up energy (water runs downhill spontaneously, giving up potential energy as it goes)
And/or
- Becomes more random and increases in entropy (complex structures decay spontaneously giving up potential energy)
69
A spontaneous process must
```
decrease enthalpy (H) and/or increase entropy (S)
Therefore spontaneous energy changes will have a negative value for their change in free energy (ΔG) as it releases energy.
```
70
Reaction Coupling
Cells use a process called “energy coupling” to carry out thermodynamically unfavourable reactions
71
ΔG = 0 is incompatible with life
Therefore reactions usually do not reach equilibrium as energy passes from the environment to the organism and back to the environment
72
metabolism
chemical process in living organism by which food is used for tissue growth.
73
Metabolic pathways
- Each step is catalysed by an enzyme
- Spontaneous reactions move toward equilibrium, but do not reach equilibrium
- Spontaneous does not mean instantaneous
- Enzymes function to selectively alter the rate of particular parts of metabolic pathways
74
Intermediary Metabolites
- Tend to be components of several pathways
| - Not very many of them compared to the number of reactions that exist in the cells of our bodies
75
Glucose degradation occurs in cells but in a series of small chemical reactions facilitated by enzymes as
Small reactions allow the potential energy to be used or stored at particular points along the pathway
76
ATP → ADP releases Free Energy which is
harnessed from this catabolic process to drive thermodynamically unfavourable reactions (+ΔG)
77
By forming ATP
An exergonic, catabolic pathway “saves” Free Energy within a system
78
Conversion of ATP to ADP is
Endergonic where anabolic pathway is “supplied” with Free Energy.
79
PEP → Pyruvate
Glucose releases its potential energy when degraded
An intermediate step in this process produces phosphoenolypyruvate (PEP)
PEP acts as an intermediate for a reaction that goes on to produce ATP during PEP to pyruvate conversion
80
Potential energy released from PEP to pyruvate conversion
is “stored” in the form of ATP
81
Potential energy in food molecules arises because they contain large numbers of H atoms:
- Carbohydrates, glucose
- Fatty acids, palmitate
Palmitate has lots of H atoms making it similar to petroleum – another molecule that is rich in energy
82
Oxidation of glucose will
release electrons that spontaneously flow through a series of intermediate steps to another chemical species, such as O2.
This can be described as an electron motive force (emf).
Emf is essentially describing electrons can accomplish work as they pass through chemical intermediates
83
activated carriers act as
coenzymes in biochemical pathways to facilitate fuel oxidation and biosynthesis reactions
84
Water importance
- It bathes our cells
- Dissolves and transports compounds
- Allows compounds to move within and between cells
- Participates in chemical reactions
- Dissipates heat
85
Water in ECF vs ICF
About 60% of your body water is within your cells (intracellular fluid [ICF])
About 30% is outside of the cells (extracellular fluid [ECF])
86
water as solovent
- Water is a polar molecule
- O is more electronegative than H, so it attracts the electrons of the covalent bonds towards it
- This gives O and H partial charges, which make it polar
87
In ice, water molecules are held in a rigid state by
hydrogen bonds
88
H-bonds are strongest when
the 3 atoms involved lie in a straight line. (bent O-H bond is weak)
This is very important biologically as it determines the very precise 3-D structures of lots of molecules such as proteins and DNA
89
A water soluble (hydrophilic) molecule can form
```
hydrogen bonds (i.e. it is polar).
eg- Sugars, Alcohols, Aldehydes, Ketones, Compounds with N-H groups
```
When these things dissolve the water-water H-bonding and solute-solute H-bonding is replaced with more energetically favourable solute-water H-bonding
90
O=O and O=C=O both have
no polarity.
The atoms lie in a straight line so the ends of the molecule are the same so a partial charge does not happen.
This makes O2 and CO2 relatively poorly water solub
91
Charged molecules are
```
water soluble (hydrophilic)
The water forms ‘screens’ around each ion keeping the NaCl in solution once dissolved
```
92
Hydrophobic effect
Non-polar (uncharged) molecules are hydrophobic.
They arrange themselves in water so as to minimise disruption of hydrogen bonding among surrounding water molecules.
This is the most energetically favourable arrangement of the molecules.
93
In clusters of lipid molecules
only the lipid portions at the edge of the cluster force the ordering of water.
This means that fewer H2O molecules are ordered and so entropy is increased
94
Amphipathic molecules contain
both hydrophobic and hydrophilic parts.
Phospholipids are amphipathic.
In water phospholipids minimise disruption of water-water H-bonds by forming micelles or bilayers
95
If you put lots of phospholipids with water then
liposomes form.
96
Hydrophobic regions of the protein chain on the
inside and hydrophilic regions on the outside
| This allows them to be water soluble
97
Hydrophobic lipids are transported in the blood in a
chylomicron.
phospholipid heads and outer edges of the proteins are all hydrophilic (i.e. polar)
They need to be or the lipids could not be transported throughout the body
cholesterol can also be found in the phospholipid bilayer.
98
Kw is the ion product of water
| Kw =
1 × 10-14 (mol/L)2
99
Water has a neutral pH because
[H+] and [OH-] are equal
100
Acidic solutions have a greater
[H+] and lower [OH-]
101
Basic solutions have a lower
[H+] and higher [OH-]
102
Hydrochloric acid (HCl; produced in the stomach)
fully dissociates into H+ and Cl- (chloride ion)
103
strong acid and alkaline substances
fully dissociate
| stronger the acid the greater its tendency to lose its proton and vice versa
104
Weak acids and bases are far more important in biological systems as they
are only partially dissociated, which gives them some unique properties
105
Optimal pH is maintained by
using buffer systems within cells and organisms
106
Acids are defined as
proton donors
| bases are proton acceptors
107
A proton donor and the corresponding proton acceptor
make up a conjugate acid-base pair
108
At midpoint of titration
pH = pKa
109
buffers in body are important for various metabolic conditions such as
- Respiratory acidosis and alkalosis
| - Metabolic acidosis and alkalosis
110
If blood did not have the bicarbonate buffer system then
the pH would fluctuate wildly as cellular products of acids (e.g. lactic acid, ketone bodies) would cause marked drops in blood pH.
It is important to maintain a blood pH of around 7.4, so patients with high acid levels will often have blood pH, [HCO3-] and [CO2] monitored
