Unit 2: Molecules And Membranes Flashcards
(38 cards)
1
Q
What are the 3 fundamental elements?
A
- Water
- Inorganic ions
- Organic molecules
2
Q
Water
A
- represents 70% (or more) of cell mass
- Polar molecule => allows it to form hydrogen bonds with each other and other polar molecules, or interact with charged ions; so is easily soluble in water (hydrophilic) and not in aqueous mediums (hydrophobic) as it is not non polar
3
Q
Inorganic Ions
A
- Represent 1% (or less) of total cell mass
- Involved in cellular metabolism and play important role in some cellular functions
4
Q
Name the inorganic ions.
A
- Sodium (Na +)
- Potassium (K +)
- Magnesium (Mg 2+)
- Calcium (Ca 2+)
- Monohydrogen Phosphate (HPO 2-)
- Chlorine (Cl -)
- Bicarbonate (HCO3 -)
5
Q
Organic Molecules
A
- 4 types: carbohydrates, lipids, proteins and nucleic acids
- Make up more than 90% of the dry weight of most cells
- All are macromolecules formed by polymerisation of low molecular weight precursors (monomers)
6
Q
What is the function of carbohydrates? (Both monosaccharides and polysaccharides)
A
- Monosaccharides: Are the main nutrient of cells and starting material for synthesis of other cellular compounds
- Polysaccharides: Are energy storing sugars and are the structural components of the cell. Also act as markers for a variety of cell recognition processes including inter-cell adhesion and transport of proteins to intracellular destinations
7
Q
Monosaccharide features
A
- Basic formula: (CH2O)n
- Can be linked to each other by dehydration and forms a glycosidic bond between the 2
_ If only a few are attached the polymer is called and oligosaccharide - Polymers of hundreds or thousands of sugars are called polysaccharides
8
Q
Other functions of carbohydrates?
A
- Cell signalling: bind to proteins acting as markers to direct proteins to cell surface or to join organelles
- Markers on cell surface: important for cell recognition and interactions between cells in multicellular tissues
9
Q
What is starch made up of?
A
2 polysaccharides; amylose and amylopectin (1:3 ratio). Amylopectin has branches α(1=>6)
10
Q
Similarities between glycogen and starch
A
- Composed of α-glucose molecules
- Glycosidic bond between C1 and C4 of another; occasionally contain α(1=>6) bonds so 2 independent chains α(1=>4) join (branches)
- Function: to store glucose
11
Q
Cellulose
A
- Main structural component of plant cell walls
- Not a branched polysaccharide
- Form fibres of great mechanical strength by joining glucose residues β(1=>4) bonds
12
Q
What are the functions of lipids?
A
- Energy source
- MAin component of cell membrane
- Cell signalling:
- Steroid hormones (estrogens, testosterone)
- Molecular messengers - carry signals from receptors to molecular targets within cells
13
Q
Characteristics of lipids
A
- simplest are fatty acids: contain long hydrocarbon chain (16-18C) with a *COO- carboxyl group at end
- Hydrophobic nature
- Stored in form of triglycerides: 3 fatty acids + 1 glycerol
- When necessary triglycerides are degraded to use as energy
- More efficient than carbohydrates (produce 2X energy per weight of degraded material)
14
Q
Characteristics of phospholipids
A
- Made up of 2 fatty acids + polar head group: Phosphate group + other polar molecule/s
- Therefore *amphipathic molecules; partly soluble and insoluble in water (have hydrophilic head group and hydrophobic tails)
- *Membrane phospholipids are typically phosphoglycerides: 2 fatty acids attached to glycerol. 3rd carbon of glycerol is attached to phosphate group, so phosphate group can bind to another small polar molecule
- Sphingomyelin = only non-glycerin phospholipid in cell membranes
15
Q
Glycolipids and Cholesterol
A
- Glycolipids made of HC chains linked to polar head groups (contain carbohydrates), therefore amphipathic
- Cholesterol made of 4 strongly hydrophobic HC rings + hydroxyl group attached to end is weakly hydrophilic, therefore also considered amphipathic
- Testosterone and Estradiol = derived from cholesterol, important in intercellular signalling
16
Q
**Nucleic acids
A
- Main information molecules of cells
- Deoxyribonucleic acid (DNA) = unique role as genetic material
- 3 types of ribonucleic acid (RNA):
- Messenger RNA (mRNA) = carries info from DNA to ribosome, template for protein synthesis
- Ribosomal RNA (rRNA) and Transfer RNA (tRNA) = involved in protein synthesis
- Others are involved in processing and transport of RNA and proteins, catalyse reactions or regulate gene expressions
17
Q
Nucleotides
A
- DNA and RNA are polymers of nucleotides
- Nucleotide: nitrogenous base (purines or pyrimidines), linked to sugars (2’-deoxyribose in DNA; ribose in RNA) phosphorylase’s at C5 of sugar
- Purines: adenine, guanine
- Pyrimidines: cytosine, thymine, uracil (RNA)
18
Q
What is the difference between a nucleotide and a nucleotide?
A
A nucleocide does not contain a phosphate group
19
Q
How to distinguish between a DNA or RNA sugar base
A
RNA contains a hydroxyl group on C2 while DNA does not
20
Q
What is formed when nucleotides are polymerised?
A
- Form nucleic acids
- Forms a phosphodiester bond between the 5’-phosphate of one nucleotide and the 3’-OH of the next (from sugar)
21
Q
What is the difference between oligonucleotides and polynucleotides?
A
- Oligonucleotides are small polymers that contain a few nucleotides
- Polynucleotides make up cellular RNA or DNA and contain thousands or millions of nucleotides respectively
22
Q
Where is information found in RNA or DNA?
A
- In the nitrogenous bases, it is transmitted by the order of the bases in the polynucleotide chains
- The bases are on the inside of the molecule, the two chains are linked by hydrogen bonds between complementary base pairs
23
Q
What other roles do nucleotides play in biological processes?
A
- ATP ( adenosine 5’ triphosphate) is the main form of chemical energy within cells
- cAMP (cyclic Adenosine Monophosphate) is used in cellular signalling pathways
24
Q
Proteins
A
- In charge of “executing” tasks defined in nucleic acids
- Most varied macromolecules and perform a range of functions:
- Structural components of cells and tissues
- Transport and storage of small molecules e.g. haemoglobin carries O2
- Information transmitters between cells (protein hormones)
- Provide defence against infection (antibodies)
- Reaction catalysts (enzymes)
25
Characteristics of proteins
- Polymers made of amino acids (a). There are 20 different aa
- Every a is made of a carbon, linked to a carboxyl group (COO-), and amino group (NH3+), a hydrogen and a side chain (R)
- The chemical properties of the a are defined by the *nature of R
26
*What are the chemical properties of each aa defined by the nature of R?
- Non polar: Do not interact with water. Chains of these aa found inside proteins
- Polar aa: Have a hydroxyl or amide group (O=C-NH2)(O=C-NH2). Hydrophilic and tend to be on outside of proteins
- Basic + Acidic aa: Very hydrophilic and often found on surface of proteins
27
Polypeptides
- Amino acids linked by peptide bonds between α-amino group of one aa and the α-carboxyl group of another
- Each chain has 2 distinct ends, one ends in an amino group (amino or *N-terminal end) and the other a carboxyl group (carboxy- or *C-terminal end)
- The aa sequence of a polypeptide is written in the same order as synthesised; from the N-terminus to the C-terminus
28
Structure of proteins
- Take on 3 dimensional configurations crucial to their function:
1. Primary structure: sequence of aa in a polypeptide chain.
2. Secondary structure: regular arrangement of aa within localised regions of polypeptide. Most common shapes: α helix and β sheet. Structures are maintained by H bonds between CO and NH groups of polypeptide bonds.
3. Tertiary structure: Folding of chain as a result of interactions between side chains of aa found in different regions of primary sequence.
4. Quaternary structure: Interactions between different polypeptide chains in proteins composed of more than 1 polypeptide.
29
*Cell membranes
Separate interior of cells from its environment
- All share same structural organisation: phospholipid biliary and associated proteins
- Proteins have specialised functions: small molecule transporters, membrane receptors, interaction between cells in multicellular organisms, electron transport and oxidative phosphorylation
30
Membrane lipids
- Phospholipids: fundamental molecules in all cell membranes
- Fatty acid tails insoluble in water so form phospholipid bilayers in aqueous media. Bilayers form stable barriers between 2 aqueous media.
- Lipids make up 50% of mass of cell membranes but depends on type of membrane
- Proportion of plasma membranes is approximately 50% lipids and 50% proteins. Membranes of mitochondria can have up to 75% mass in proteins.
31
Lipid Bilayers
- behave like 2 dimensional fluids: individual lipids and proteins can rotate and move in lateral directions (even 1 monomer to the other)
- Fluidity is crucial and depends on temperature and lipid composition: short chain fatty acid interactions are weaker than longer ones => less rigid so maintain fluidity at lower temps better
32
What is the role of cholesterol in lipid bilayers?
They insert into bilayers with its polar hydroxyl groups close to hydrophilic head groups of phospholipids. The HC rings interact with the hydrophobic chains of fatty acids => reduces mobility + *increases rigidity while maintaining fluidity at low temps.
33
What are the 2 types of membrane proteins?
1. Integral membrane proteins: embedded in the bilayers. Some are transmembrane proteins (go through membrane completely). Parts that pass through membrane are 20-25 non-polar aa α helical regions. Another that passes is the β-barrel, this is mainly found in bacteria, chloroplasts + mitochondria.
2. Peripheral membrane proteins: not inserted in membrane but are indirectly associated, mainly through interaction with other proteins.
34
Characteristics of membrane proteins
- Amphipathic molecules
- Some pass through membrane multiple times
- in eukaryotes most are modified by carbohydrates (glycoproteins) exposed on the cell surface playing a role in intercellular signalling and recognition
- Proteins can be anchored to membrane by lipids covalently linked to the polypeptide chain
35
Transport across membranes
- Selectively permeable to small molecules, allows cell to control and maintain composition
- Only small, uncharged molecules can pass freely through bilayer
36
What are the 2 groups of membrane transporters?
1. Protein channels: form pores in membrane. Ion channels allow inorganic ions like Na+, K+, Ca2+ and Cl- to pass. Pores can be selectively opened or closed in response to extra cellular signals.
2. Carrier proteins: Selectively bind and transport specific molecules e.g. glucose. Undergo conformational changes to aid passage pf molecules through membrane
37
What are membrane transporters?
Transmembrane proteins that allow substances to pass through the lipid bilayer if they cannot do so freely.
38
What is the difference between active and passive transport?
Active transport moves molecules in an energetically unfavourable direction and therefore requires energy in the form of ATP. Can only transport using carrier proteins.
Passive transport uses both membrane transporters and is determines by conc. and electrochemical gradients, therefore does not require energy.
