Molecules, Cells and Variation - 1.1 +1.2 Flashcards
Maltose
Disaccharide made from glucose and glucose
Sucrose
Disaccharide made from glucose and fructose
Lactose
Disaccharide made from glucose and galactose
Hydrolysis of disaccharide
Boiling with acid
Benedict’s test for reducing sugars
- Small amount of sample is placed in test tube with 2cm3 of Benedict’s solution.
- This is heated in water bath for 5 mins.
- Brick red/orange colour (produced by copper (I) oxide) is a +ve result.
- If solution remains blue – no reducing sugar present.
Test for non-reducing sugars
- Carry out Benedict’s test on sample to confirm -ve
- Hydrolyse another sample by heating with dilute acid e.g. HCl or by using the enzyme sucrase at its optimum temperature.
- When cooled, add dilute NaOH solution to neutralise the acid.
- Add Benedict’s solution, heat in water bath for 5 mins.
- +ve brick red colour indicates non-reducing sugar (sucrose) was originally present.
Polysaccharides
- Polysaccharides differ in number and arrangement of glucose molecules they contain.
- Function as storage or structural molecules, as they’re large and relatively insoluble in water.
- They are non-reducing.
- They are unsweet to taste.
Cellulose
Long-straight chains, which collectively form microfibrils, which together form macrofibrils.
In one layer, macrofibrils go the same direction, across layers they go different directions. Layers are interwoven causing rigidity. Fully permeable.
Starch
Storage molecule in plants. Stored in amyloplasts in the cytoplasm. Comprised of amylose and amylopectin.
Hydrolysis of starch
Hydrolysed by amylase to produce maltose
Why is starch suitable as a storage molecule?
- Insoluble and osmotically inactive.
- Molecule has helical shape forming compact store.
- Contains large number of glucose molecules providing abundant supply of respiratory substrate.
- Too large to cross cell membrane, remains in cell.
Glycogen
Storage molecule found in animals and fungi. Similar to starch but with is more branched so can be hydrolyzed more rapidly to release glucose for respiration.
Amyloplasts
Starch grains found in cytoplasm of plant cells. Contain the polysaccharide starch.
What properties of glycogen make it ideal for storage?
Insoluble and osmotically inactive
Stored in liver and muscle tissues
Difference in elements between lipids and carbohydrates.
Lipids possess more hydrogen and less oxygen.
Triglycerides
Type of lipid formed by joining 3 fatty acids to one glycerol molecule during a condensation reaction with the loss of three water molecules.
Hydrolysis of lipids
- Heating with acid or alkali.
- Using the enzyme lipase at its optimum temperature and pH.
Bond between two monosaccharides
Glycosidic bond
Amylose
Long, unbranched chain of a-glucose. Angles of glycosidic bonds give a coiled sructure, like a cylinder. Makes it compact, so is good for storage.
Amylopectin
Long, branched chain of a-glucose. Side branches allow easy break down by enzymes as bonds are easily accessed. Allows fast release of glucose.
In cellulose, why is every other B-glucose molecule inverted?
β1-4 glycosidic bond joining the β glucose molecules together. Creates long, straight chain.
Why do microfibrils occur with cellulose?
Hydroxyl (OH) groups project from either side of glucose chains form hydrogen bonds with the hydroxyl (OH) groups of adjacent chains
How are macrofibrils positioned and what does this allow?
Macrofibrils in one layer are orientated in the same direction. In successive layers, they’re orientated in a different direction. They are interwoven and embedded in a matrix providing rigidity. Cellulose cell wall is usually fully permeable due to minute channels between the different layers of macrofibrils.
What allows amylopectin to branch?
a1-6 bonds glycosidic bonds
endopeptidases
Hydrolyse internal peptide bonds in proteins to produce smaller polypeptides.
exopeptidases
Remove single amino acids from the ends of the polypeptide chains, eventually producing dipeptides and amino acids
Secondary structure
Hydrogen bonds form between AA in chain. Cause alpha helix or beta pleated sheet
Tertiary structure
Further coiling/folding. Hydrogen, ionic and disulphide bonds form. Also hydrophobic interactions.
Disulphide bonds
Tertiary structure of proteins, occur between cysteine amino acids.
Quaternary structure
Relates to highly complex proteins consisting of more than one polypeptide chain and possibly the association of non-protein/prosthetic groups. Same bonds as 3rd.
Hydrogen bonding in proteins
Between C=O and N-H groups of backbone. Responsible for secondary structures. Can also occur in R groups.
Fibrous proteins
Have structural functions e.g. keratin-nails&collagen-bone. Insoluble, w/ simple tertiary and quaternary structure consisting of long parallel polypeptide chains. Often form fibres or sheets providing strength and flexibility.
Globular proteins
Consist of highly folded and coiled polypeptide chain. Produces compact, complex specific tertiary structure, which is soluble in water. Includes enzymes, antibodies, receptors and hormones.
Causes of denaturation
High temperatures above the optimum, breaking hydrogen bonds.
Changes in pH away from the optimum break hydrogen and ionic bonds.
Reducing agents can break disulfide bridges.
Heavy metal ions can bind to sites on the protein and bring about changes in shape.
Biuret test
Test for proteins
Add sample to test tube containing 2cm3 of biuret reagent.
A purple/lilac colour indicates protein is present.
If the solution remains blue, no protein is present.
Enzyme
Globular proteins, usually with a high molecular weight. Biological catalysts which regulate biological processes in living organisms. Tertiary structure of enzyme determines its specific function.
Amylase
Breaks down starch
Lipase
Hydrolyses ester bonds
Enzyme specificity
Feature of the unique tertiary structure of an enzyme.
Structure is held together by hydrogen bonds, ionic bonds and sometimes disulphide bridges.
This determines the shape and electrostatic charges of the active site
Induced fit hypothesis
Substrate interacts with active site and causes enzyme to change shape. This may put a strain on bonds of substrate making a reaction more likely e.g. hydrolysis.
Active site may also allow two molecules to come very close together, in a certain orientation, making a reaction more likely (e.g. a condensation reaction)
High temperatures and enzymes
There is a very high level of kinetic energy and the reaction proceeds at a very fast rate due to many collisions between enzyme and substrate. However, due to the very high kinetic energy, hydrogen bonds begin to break and the enzyme begins to denature. Therefore less or no substrate can bind at the altered active site. The reaction stops but there is still substrate left at the end.
How can the impact of a competitive inhibitor be reduced?
Addition of more substrate
End-product inhibition
When the end product of a metabolic pathway begins to accumulate, it may act as an inhibitor. Product starts to switch off its own production as it builds up. Process is self-regulatory. As the product is used up, its production is switched back on again. Called end-product inhibition, example of negative feedback.
Immobilised enzymes
Binding to, or trapping in, a solid support which can be recovered easily from the reaction mixture. Enzyme can be re-used, reducing cost of process.
Advantages of immobilising enzymes
Cost
Restricts enzymes ability to change shape&denature
Allows continuous production
Physical bonding methods of immobilising an enzyme
- Adsorb onto insoluble matrix, such as collagen
- Hold inside gel, such as silica gel (gel entrapment)
- Hold within semi-permeable membrane e.g. polymer microspheres
- Trap in a micro-capsule (microencapsulation) e.g. in alginate beads
Chemical bonding example of immobilising enzyme
To the support medium e.g. using glutaraldehyde to bind the enzyme to cellulose fibres. Enzymes are covalently bonded, enzyme activity is high. Although preparation is difficult.
How does an electron microscope work?
It uses a beam of electrons focused by electromagnets.
How does a light microscope work?
Focuses light rays by lenses in light microscopy.
Wavelength of electron microscope?
0.005nm
Wavelength of light microscope?
500-700nm
Maximum resolution of electron microscope?
0.05nm
Maximum resolution of light microscope?
200nm
Advantages of electron microscope
- High maximum useful magnification (over a million)
- Electrons have shorter wavelength than light and thus greater resolution
Resolution
The ability to distinguish between two close objects
Disadvantages of electron microscope
- Vacuum is required, so no living specimens.
- Complicated preparation and staining techniques which can produce artefacts
- Expensive, and expert training is required to use.
Transmission electron microscope process
- Beam of electrons transmitted through specimen.
- Specimen must be thin
- Stained using electron dense substances such as heavy metal salts
- These deflect electrons in beam, the pattern the remaining electrons produce whilst passing through is converted to an image.
Limitations of TEM
- Very thin sections of the specimen must be used
- Doesn’t show 3D arrangement of cellular components.
- Specimen gradually deteriorates in electron beam.
Advantages of TEM
- Higher resolution than SEM
- Can see internal structures even of molecular size e.g. proteins and nucleic acids
Scanning electron microscope process
- Specimen is coated with thin film of heavy metal (e.g.gold)
- Electron beam scanned to and fro across specimen
- Reflected electrons from surface are collected and produce an image on screen.
Advantages of SEM
- Surfaces of structures are shown
- Gives a three-dimensional effect
- Much thicker sections can be examined than TEM
Limitations of SEM
- Lower resolution than TEM
- Only the surface of an object can be viewed.
Consistent structures present in prokaryotes
- Cell wall (murien/peptidoglycan)
- Cell membrane
- Circular genomic DNA (attached to mesosome)
- Ribosomes
- Food reserve granule (lipid or glycogen)
- Cytoplasm
Differential Centrifugation
- Centrifugation separates structures of different densities.
- Differential centrifugation involves centrifuging at different speeds (forces) and can be used to separate and isolate the different organelles in a cell.
Hypotonic
Extracellular fluid has lower osmolarity than fluid inside cell, so net flow of water goes into cell.
Hypertonic
Extracellular fluid has a higher osmolarity than the cell’s cytoplasm, so water moves out of cell to region of higher solute concentration.
Plasmolysis
Contraction of protoplast of plant cell due to water loss
Centrioles
- Produce spindle fibres that seperate chromosomes during mitosis/meiosis.
- Small hollow cylinders containing microtubules.
Importance of cristae
- Provide large surface area for stalked particles they possess
- These contain enzymes used for ATP production by the electron carrier system (oxidative phosphorylation)
Importance of matrix
- Contains enzymes of Kreb’s cycle (aerobic respiration)
- Contains mitochondrial DNA and ribosomes.
- DNA contains information for organelle replication
- Ribosomes required for protein synthesis
What do ribosomes consist of?
Two subunits, one small, one large.
Made of protein and ribosomal RNA.
What does the rough endoplasmic reticulum consist of?
- Has ribosomes on surface that produce secretory proteins that are transported through the cisternae.
- Proteins are sent to the Golgi body for packaging.
Smooth endoplasmic reticulum
Involved in production and transport of lipids.
Location of ribosomes
Present in the cytoplasm singly, in a chain (polysomes) or attached to the RER
Golgi body
Acts as an internal processing and transport system.
- Produces glycoproteins
- Packages and secretes proteins
- Forms lysosomes and cell walls.
- Lipid biosynthesis.
Lysosomes
Spherical w/ single membrane. Contains hydrolytic enzymes
Enzymes found in lysosomes
Proteases, nucleases and lipases.
Have to be kept apart from the rest of the cell.
Enzymes contained were synthesised on RER and transported to Golgi apparatus.
Functions of lysosomes
Digestion of material taken in by endocytosis
Autophagy
Release of enzymes outside the cell
Autophagy
Process by which unwanted structures within cell are engulfed and digested within lysosomes.
First enclosed by single membrane, from SER. This structure fuses w/ lysosome to form ‘autophagic vacuole’ wherethe unwanted material is digested. Part of normal turnover of cytoplasmic organelles, old ones replaced by new ones.
Stroma
Fluid in chloroplasts.
Site of light-independent reaction
Contains enzymes, sugars and amyloplasts.
Chloroplasts
Site of photosynthesis.
Flattened biconvex discs, surrounded by envelope made of two membranes.
Envelope encloses membrane system of thylakoids, which form stacks of grana.
These provide large surface area for chlorophyll for the light-dependent reactions of photosynthesis.
Membrane system is surrounded by the stroma
Tissue
Aggregations of similar cells that perform a specific physiological function
Organ
Structure consisting of different tissues, which has a specific physiological function
System
Several organs combined
How are palisade mesophyll cells adapted for photosynthesis?
Possess numerous chloroplasts.
Have relatively thin cell walls.
Are cylindrical.
There are with few air spaces in between.
What is an advantage of having thin cell walls in plant cells?
Allow carbon dioxide to diffuse in at a faster rate.
What is an advantage of palisade mesophyll cells being cylindrical?
Have a relatively large surface area increasing the rate of gaseous diffusion.
What is an advantage of palisade mesophyll cells having few air spaces between one another?
Allows maximum light absorption.
Epithelial tissues
Line inside/outside or organs and have a range of functions.
Can be categorized into 3 types: squamous, cuboidal and columnar.
Columnar tissues
Found in small intestine and proximal convoluted tubule of the kidney. Cylindrical in shape and specifically adapted for absorption of small molecules, mainly by active processes. Have microvilli+mitochondria.
Process of cloning plants in vitro
A few cells are taken from the plant and are placed in a suitable nutrient medium. Growth factors e.g. IAA are applied to stimulate the totipotent cells to differentiate into shoots and roots.
Other than rapid production of a multiple clones of a particular plant, what else is cloning plants in vitro used for?
- Produce clones of plants w/ desirable traits .
- To quickly produce mature plants.
- Regeneration of plants from GM cells
Difference between totipotent and pluripotent stem cells?
Totipotent stem cells can produce extra embryonic tissue
Three primary germ layers pluripotent cells can differentiate into
ectoderm - outside layer
endoderm - innermost layer
mesoderm - middle layer
Uses of stem cells
- research into chemical signals that cause cells to differentiate to specific cells
- carry out drug tests on differentiated cells formed from stem cells, reducing the amount of drug testing on animals.
Features increasing membrane permeability of plasma membranes
Unsaturated fatty acids
Abundance of channel/carrier proteins
Large areas of phospholipid
Features decreasing membrane permeability of plasma membrane
Saturated fatty acids
Cholesterol
Lack of bilayer
Lack of proteins
Role of receptor proteins on surface
Bind to hormones due to specific tertiary structure and trigger a cellular response
Diffusion
The net movement of molecules down a concentration gradient from an area of high concentration to an area of low concentration until the molecules are equally distributed.
Rate of diffusion
SAxCG/DD
Facilitated diffusion
The transport of polar molecules (e.g.glucose, amino acids) and charged species(e.g.ions) across membranes.
Carrier proteins
Span bilayer and change shape in presence of specific complementary molecule.
Can be specific to single molecules or groups of similar molecules.
Channel proteins
Retain shape and transport ions.
Charge of channel causes specificity.
Pore size also determines passage of ions.
Active transport
Movement of molecules/ions through a partially permeable membrane by carrier proteins against a concentration gradient.
Factors affecting respiration rate and thus active transport
Temperature.
Volume of oxygen.
Metabolic and respiratory inhibitor
Osmosis
Net movement of water molecules from a dilute solution to a more concentrated solution across a selectively permeable membrane.
Pinocytosis
Material taken up is in liquid form. Vesicles formed are v small, in which case the process is known as micropinocytosis and the vesicles as micropinocytotic vesicles.
Endocytosis and exocytosis
Active processes involving the bulk transport of materials through membranes, either into cells (endocytosis) or out of cells (exocytosis)
Cisternae
Flattened membrane sacs which make up the golgi body and the ER, where they form an internal cell transport system.
