Foundations In Biology Flashcards
Outline how a student could prepare a temporary mount of tissue for a light microscope
Obtain thin section of tissue
Place plant tissue in drop of water
Stain tissue on a slide
As coverslip using mounted needle
Describe how light microscopes work
Lenses focus rays of light and magnify
Different structures absorb different amounts of light
Reflected light is transmitted to the observer via objective lens and eyepiece
Describe how a transmission electron microscope works
Beam of electrons through specimen
More dense structures appear darker
Focus image onto flourescent screen or photographic plate using magnetic lenses
Describe how a scanning electron microscope works
Focus beam of electrons onto surface using electromagnetic lenses
Reflected electrons hit a collecting device and are amplified to produce an image on a photographic plate
How a laser scanning confocal microscope works
Focus laser beam using objective lenses
Pluorophores in the sample emit photons
Photomuliplier tube amplifies the signal onto a detector an image is produced pixel by pixel
Calculate actual size
Actual size=image size/ magnification
Define magnification and resolution
Magnification=factor by which the image is larger than the actual specimen
Resolution=smallest separation distance at which 2 separate structures can be distinguished from each other
Why do samples need to be stained
Facilitates absorption of wavelengths of light to produce image and to differentiate structures
Mag. And res of a light microscope
Mag=×2000
Res=200nm
Mag and res TEM
Mag=×500000
Res=0.5nm
Mag and res SEM
Mag=×500000
Res=3-10nm
How to use an eyepiece graticule and stage micrometer
Place micrometer on stage to calibrate eye piece graticule
Count how many graticule divisions are in 100micrometers on the micrometer
Length of 1 eyepiece division=100 micrometers/ number of divisions
Use calibrated values to calculate actual length of structures
7 biologically important properties of water
Maximum density at 4°c
High surface tension
Incompressible
Solvent
High specific heat capacity
High latent heat of vaporisation
Cohesion
Why is it good for water to be incompressible
Provides turgidity to plant cells
Provides hydrostatic skeleton for some small animals like earthworms
Explain why ice floats on water
I’ve is less dense because of hydrogen bonds
Insulates water so aquatic organisms can survive
Why is it good for water to have high surface tension
Slows water loss due to transpiration
Some insects can skim across the surface of water
Water as a solvent
Dissolves and transports charged particles involved in intra&extracellular reactions
High specific heat capacity and high latent of vaporisation of water
Acts as a temperature buffer
Cooling effect when water evaporates from skin
Define monomer and polymer
Monomer:smaller units that join together to form larger molecules.
Polymer:formed when monomers join together
What happens in condensation and hydrolysis reactions
Condensation: Bond forms and water is produced
Hydrolysis: water is used to break a bond
Properties of alpha glucose
Small and water soluble- easily transported in blood stream
What type of bonds between monosaccharides
1,4 or 1,6 glycosidic bonds
3 disaccharides
Maltose: glucose and glucose
Sucrose:glucose and fructose
Lactose:glucose and galactose
Structure and function of starch
Storage polymer of alpha glucose
Insoluble, large
Made from amylose:1,4 glycosidic bonds helix shape and compact
Made from amylopectin: 1,4&1,6 glycosidic bonds branched
Structure and function of glycogen
Storage polymer of alpha glucose in animals
1,4 and 1,6 g bonds
Branched
Insoluble
Compact
Structure and function of cellulose
Polymer of beta glucose gives rigidity to plant cell walls
1,4 g bonds
Straight chain-unbranched
Alternate glucose molecules rotated 180°
H-bond crosslinks between parallel strands form microfibrils- high tensile strength
How do triglycerides form
Condensation reaction between 1 glycerol and 3 fatty acids forming ester bonds
Structure and function of triglycerides
High energy: mass ratio= high calorific value (energy storage)
Insoluble hydrocarbon chain= used for waterproofing
Slow conductor of heat= thermal insulation
Less dense than water= buoyancy
Structure and function of phospholipids
Glycerol backbone 2 hydrophobic fatty acid tails and 1 hydrophilic polar phosphate head
Forms phospholipid bilayer
General structure of an amino acid
COOH group
R variable group
NH2 amine group
How polypeptide form
Condensation reaction forms peptide bonds
Primary and secondary protein structure
Primary-sequence number and type of amino acids
Secondary- h-bonds form alpha helix and beta pleated sheets
Tertiary protein structure
Disulfide bridges
Ionic bonds
Hydrogen bonds
Hydrophobic/phillic interactions
Quaternary protein structure
More that one poly peptide chain
Structure and function globular proteins
Spherical and compact
Usually water soluble
Involved in metabolic processes e.g amylase, insulin and haemoglobin
Structure and function of fibrous proteins
Can form long chains or fibres
Insoluble in water
Structural function
Functions of collagen elastin and keratin
Collagen: component of bones cartilage tendons etc
Elastin: elasticity to arteries,skin,lungs,cartilage,ligaments
Keratin: component of hair,nails,hooves,claws,epithelial cells of outer skin layer
Test for proteins
Buiret test
Equal volumes of sodium hydroxide to sample
Drops of copper(II) sulfate solution
Mix
Positive result= blue->purple
Test for lipids
Dissolve in ethanol
Add equal volume of water and shake
Positive result= milky white emulsion
Test for reducing sugars
Add benedicts reagent
Heat in water bath 100°c for 5 mins
Positive result= blue-> orange&brick red precipitate forms
Test for non reducing sugars
Hydrolyse non reducing sugars by adding 1cm^3 of HCl heat for 5 mins
Neutralise solution with sodium carbonate solution
Proceed with usual benedicts test
Test for starch
Add iodine
Positive = orange->blue black
Measure the concentration of a solution quantitavely
Use colorimetry to measure absorbance
Use biosensors
Rf values
Ratios that allow comparison of how far molecules have moved in chromatograms
Rf value=distance between origin and centre of pigment spot/ distance between origin and solvent front
Pentose sugars in DNA &RNA
DNA= deoxyribose
RNA=ribose
How polynucleotide strands are formed and broken down
Condensation between nucleotides dorm phosphodiester bonds hydrolysis reactions break these bonds
Enzymes catalyse these reactions
Structure of DNA
Double helix of 2 polynucleotide strands H-bonds between complementary base pairs (AT and CG) in strands that run antiparallel
Purine bases
Adenine and guanine
Two ring molecules
Primitive bases
Thymine cytosine uracil
One ring molecules
Complementary base pairs
DNA 2 h bonds AT
RNA-2 h bonds AU
both- 3 h bonds GC
What is semiconservative replication
Strands from original DNA act as templates
Role of DNA helicase
Breaks h bonds between base pairs to form 2 single strands
How is a new strand formed in semiconservative replication
Free nucleotides attach to exposed bases
DNA polymerase joins adjacent nucleotides in a 5’->3’ direction to form phosphodiester bonds
H bonds reform
Features of the genetic code
Non-overlapping
Degenerate
Universal
How does a gene determine the sequence of amino acids
Consists of base triplets that code for specific amino acids
Transcription
Produces mRNA
Occurs in nucleus
Process of transcription
RNA polymerase binds to promoter region on gene
DNA uncoils so exposed bases
Free nucleotides attach to complementary bases
RNA polymerase joins adjacent nucleotides
After transcription
RNA polymerase detaches
H bonds reform and DNA rewinds
Splicing removes introns from pre-mRNA in eukaryotic cells
mRNA moves out of nucleus via nuclear pore &attaches to ribosome
Translation
Produces proteins
Occurs on ribosomes
Process of translation
Ribosome moves along RNA until start codon
tRNA anticodon attaches to complementary bases on mRNA
Condensation reactions between between AA on tRNA form peptide bonds requires energy
Process continues to form polypeptide chain until stop codon
Structure of ATP&ADP
Nucleotide derivative of adenine
ATP has 3 inorganic phosphate groups
ADP has 2
What is a mutation
An alteration to the DNA base sequence
What are enzymes
Biological catalysts
Example of an enzyme that catalyses an intracellular reaction
Catalase -decomposition of hydrogen peroxide into water and oxygen
Examples of enzymes that catalyse extracellular reactions
Amylase and trypsin
Induced fit model
Conformational change enables ES complexes to form, puts strain on substrate bonds , lowering activation energy
Lock and key model
Complementary to 1 substrate formation of ES complex lowers the activation energy
5 factors that affect the rate of enzyme controlled reactions
Enzyme concentration
Substrate concentration
Inhibitor concentration
pH
Temperature
Substrate concentration
Rate increases proportionally to substrate concentration until no more enzymes left
Enzyme concentration
Rate increases proportionally to enzyme concentration until no more substrate
Temperature on rate of enzyme action
Increases ans kinetic energy increases until bonds start to break and it is denatured
Temperature coefficient
Q10 measures change in rate of reaction per 10°c temperature increase
Q10= rate2/ rate 1
pH rate of enzyme action
Outside range protons/ OH- ions interfere with bonds
Competitive inhibitors
Bind to active site (similar to substrate) temporarily prevent ES complexes forming , increasing substrate concentration decreases their affect
Non-competitive inhibitors
Bind elsewhere on enzyme trigger change in active site shape
Substrate concentration has no impact
End product inhibition
One of the products in a reaction acts as an inhibitor for an enzyme in the pathway preventing further formation of products
Metabolic poison
Damages cells by interfering with metabolic reactions , usually an inhibitor
Examples of metabolic poisons
Cyanide
Malonate
Arsenic
Inactive precursors in metabolic pathways
To prevent damage to cells
One part of the precursor acts as an inhibitor
Cofactors
Non-protein compounds required for enzyme activity
coenzymes
Do not bind permanently, often transport molecules or electrons between enzymes
Inorganic cofactors
Facilitate temporary binding between substrate and enzyme oftem metal ions
Eg. Cl- is the cofactor for amylase
Prosthetic groups
Tightly bound cofactor act as a permanent part of enzymes binding site e.g. zn2+ for carbonic anhydrase
Fluid mosaic model
Phospholipid bilayer in which individual phospholipids can move membrane has flexible shape extrinsic and intrinsic proteins are embedded
Fluid mosaic model
Phospholipid bilayer in which individual phospholipids can move membrane has flexible shape extrinsic and intrinsic proteins are embedded
Role of cholesterol &glycolipids in membranes
Cholesterol: steroid molecule in some plasma membranes connect phospholipids and reduces fluidity to make bilayer more stable
Glycolipids: cell signalling and recognition
Function of extrinsic proteins in membranes
Binding sites /receptors
Antigens
Bind cells together
Involved in cell signalling
Function of intrinsic transmembrane proteins in membranes
Electron carriers, Channel proteins ,carrier proteins
Function of membranes inside cells
Internal transport system, selectively permeable to regulate movement into/out of organelles
Provide a reaction surface
Isolate organelles from cytoplasm for specific metabolic reactions
Function of the cell surface membrane
Isolates cytoplasm from extracellular environment
Selectively permeable regulate transport of substances
Involved in cell signalling / recognition
3 factors that effect membrane permeability
Temperature
pH
Solvent
How colorimetry can investigate membrane permeability
Plant tissue with soluble pigment in vacuole. Tonoplast and cell surface membrane disrupted = more permeability = pigment dissolves into solution
Select colorimeter filter with complementary colour
Use water to set colorimeter to 0
Measure absorbance/ transmission
High absorbance= more pigment
Osmosis
Water diffuses across semi permeable membranes from an area of high water potential to an area of low water potential
What is water potential
Pressure created by water molecules measured in kPa
Pure water =0
More solute = more negative
Osmosis affect plant and animal cells
Into:
Plant- turgid animal-lysis
Out:
Plant-flaccid, animal- crenation
Simple diffusion
Passive process- no energy
Net movement of small lipid soluble molecules from area of high conc to low conc
Facilitated diffusion
Passive process
Specific channel or carrier proteins with complementary binding sites transport large/ polar molecules/ ions down a concentration gradient
Explain how channel and carrier proteins work
Channel: hydrophilic channels bind to specific ions one side closes and the other opens
Carrier: binds to complementary molecule = conformational change releases molecules on other side
Active transport
Active process ATP hydrolysis releases phosphate group that binds to a carrier protein causing it to change shape
Specific carrier proteins transports molecules/ions from an area of low conc to an area of high conc
Exocytosis and endocytosis
Active process
Bulk transport and transporting large particles
Vesicles fuse with cell surface phospholipid membrane
5 factors affecting rate of diffusion
Temperature
Diffusion distance
Surface area
Size of molecule
Difference in concentration
The cell cycle
Regulated cycle of division with intermediate growth periods
Interphase
Mitosis/meiosis
Cytokinesis
Interphase
G1: cell synthesises proteins for replication & cell size doubles
S: DNA replicates
G2: organelles divide
Purpose of mitosis
Produces 2 genetically identical daughter cells for
Growth
Cell replacement/ tissue paper
Asexual reproduction
Stages of mitosis
Propose
Metaphase
Anaphase
Telophase
Prophase
Chromosomes condense
Centrioles move to opposite poles and spindle forms
Nuclear envelope and nucleuolus breakdown
Metaphase
Sister chromatids line up at the cell equator attached to the spindle by their centromeres
Anaphase
Requires energy
Chromatids separate and are pulled to opposite poles of cell
Telophase
Chromosomes decondence
New nuclear envelope reforms
Cytokinesis
Cell membrane cleavage furrow forms
Contractile division of cytoplasm
Cell cycle regulated
Checkpoints regulated by by cell-signalling proteins ensure damaged cells do not progress to next stage of cycle
Cyclin-dependent kinase enzymes phosphorylate proteins that initiate next phase of reactions
What happens at each checkpoint
Between G1 and S cell checks for DNA damage
Between G2 and M cell checks chromosome replication
At metaphase checkpoint cell checks that sister chromatids have attached to spindle correctly
Meiosis
A form of cell division that produces four genetically different haploid cells with half the number of chromosomes found in the parent cell known as gametes
What happens during meiosis I
Homologous chromosomes pair to form bivalents
Crossing over Occurs at chiasmata
Cell divides into two homologous chromosomes separate randomly each cell contains either maternal or paternal copy
Homologous chromosomes
Pair of chromosomes with genes at the same locus 1 maternal and 1 paternal some alleles may be same while others are different
Meiosis II
Independent segregation of sister chromatids
Each cell divides again producing 4 haploid cells
Meiosis II
Independent segregation of sister chromatids
Each cell divides again producing 4 haploid cells
How does meiosis produce genetic variation
Crossing over during meiosis I
Independent assortment of homologous chromosomes &sister chromatids
Result in a new combination of alleles
How do cells become specialised
Some genes are expressed while others are silenced . Cells produce proteins that determine their structure and function
What is a transcription factor
A protein that controls the transcription of genes so only certain parts of the DNA are expressed
How do transcription factors work
Move from the cytoplasm into nucleus
Bind to promoter region upstream of target gene
Makes it easier or more difficult for RNA polymerase to bind to gene this increases or decreases rate of transcription
Stem cells
Undifferentiated cells that can divide indefinitely and turn into other specific cell types
4 types of stem cell
Totipotent-can develop into any cell type including the placenta and embryo
Pluripotent- any cell except placenta and embryo
Multipotent- only develop into a few different types of cell
Unipotent- only develop into one type of cell
Uses of stem cells
Repair damaged tissue
Drug testing
Treating neurological diseases
Researching developmental biology
2 types of specialised cells
Erythrocytes- biconcave,no nucleus, haemoglobin
Leucocytes-lymphocytes,eosinophil,neutrophils,monocytes
Structure of squamous and ciliated epithelia
Squamous: smooth layer fixed in place by basement membrane
Ciliated: made or ciliated epithelial cells
Meristems
Totipotent undifferentiated plant cells that can develop into various types of plant cell including xylem vessels and phloem sieve tubes
Structure of phloem tissue
Sieve tube elements - form a tube
Companion cells - involved in atp production
Plasmodesmata- gaps where cytoplasm links
