Key Points Document Flashcards
Cell wall function
Provides rigid shape
Stops osmotic lysis
Outline the roles of organelles in the production, transport and release of proteins from eukaryotic cells
DNA in nucleus codes for the protein
Ribosomes on the RER produce the protein
Mitochondria produce ATP needed for protein synthesis
Golgi apparatus modifies and packages protein into
vesicles
Vesicles transport the protein to the cell surface membrane where they fuse with it and undergo exocytosis to desired location
Compare and contrast DNA in prokaryotes and eukaryotes
Nucleotide structure identical
Nucleotides joined by phosphodiester bonds
Deoxyribose sugar
DNA in chloroplast and mitochondria similar to prokaryote
Eukaryotic longer
Eukaryotic contains introns
Eukaryotic is linear, Prokaryotic circular
Eukaryotic membrane bound, Prokaryotic free floating
Eukaryotic associated with histone
Differences between plant and prokaryotic DNA
Plant associated with histones, Prokaryotic not Plant linear, Prokaryotic circular Plants have no plasmids, Prokaryotes do Plants have introns, Prokaryotes do not Plants longer
How is cholera different to epithelial cells
Cholera is prokaryotic, epithelial Eukaryotic
Cholera has no nuclear membrane and DNA free floating and circular
Cholera has no membrane bound organelles
Or SER/RER
Cholera only has small ribosomes
Cholera has a flagella, capsule, plasmid or cell wall
Advantage of TEM over SEM
Higher resolution
Higher magnification so more detail/internal details to be seen
Cross sections can be taken
Advantage of SEM over TEM
Can be 3D
Thin sections do not need to be prepared
Shows surface of specimen
Advantages vs disadvantages of TEM
Small objects can be seen
High resolution
Electrons wavelength is shorter than light
Cant look at living cells, must be dead
Must be a thin specimen
Must be in a vacuum
Risk of creating artefacts in preparation
Why isotonic
Prevents osmosis so organelle doesn’t burst of shrivel
Why ice cold
Reduce enzyme activity so organelles are not digested
Why add a buffer
Maintain a constant pH so proteins do not denature
How can cell fractionation and centrifugation be used to isolate mitochondria from a suspension of animal cells
Cell homogenisation to break open cells and release organelles
Filter to remove large debris like cell walls
Use isotonic solution to prevent osmotic damage to mitochondria
Keep ice cold to prevent damage to organelles by enzymes
Use a buffer to maintain pH so proteins don’t denature
Use differential centrifugation to separate nucleus in first pellet since densest
Re spin supernatant at a higher speed and the next pellet is mitochondria
Observe with microscope to check it is mitochondria
Why fluid mosaic
Fluid because molecules can move around within the membrane
Mosaic because made up of a variety of different molecules unevenly distributed
How is movement across cell membrane affected by membrane structure
Phospholipid bilayer allows lipid soluble substances to enter by simple diffusion
Stops polar, charged and water soluble molecules entering
Carrier proteins allow active transport
Channel and carrier proteins allow facilitated diffusion
Cholesterol affects permeability
Surface area determines how much diffusion
Number and type of channel proteins and carrier proteins determines how much is transported and what is transported
Non-specific defence mechanisms against pathogen
Phagocytosis Pathogen engulfed by phagocyte Entering its cytoplasm in a vesicle Lysosomes fuse Releasing hydrolytic digestive enzymes Lysozymes break down the pathogen Waste ejected from cell via exocytosis Becomes and APC
Cells that can stimulate an immune response
Abnormal body cells
Pathogens
Cells from other organisms like transplant
Cells infected by virus
How do vaccines cause production of antibodies
Vaccine contains antigens from pathogen
Macrophage presents the antigens on its cell
T helper cell with complementary receptor protein binds to antigen
Stimulating specific B cell with complementary antibody on its surface
B cell divides by mitosis in clonal selection
Producing more of the antibody
And memory B cells
B cells secrete large amounts of antibody
How does the humoral response lead to immunity
B cells specific to antigen undergo clonal selection by mitosis
B cells produce plasma cells and memory cells
Second infection produces antibodies quickly in large volumes
Role of antibodies in stimulating phagocytosis
Bind to antigen and act as markers for opsonisation
Clump pathogens together so easier to destroy
Active vs passive immunity
Active involves memory cells
Active involves production of antibody by plasma cells
Passive involves antibody introduced from external source
Active is long term because antibody produced in response to antigen
Passive is short term since antibody is broken down
Active can take longer to develop and passive is faster acting
Monoclonal antibody
Antibodies produced from a single clone of B cells
Why are monoclonal antibodies specific
Specific primary structure
Specific tertiary structure
So can only bind to one type of antigen
Structure of HIV
Human Immunodeficiency Virus
RNA is the genetic material
Reverse transcriptase contains genetic blueprint to rewrite human gene to manufacture viral particles
Protein capsid
Phospholipid envelope made from cell membrane of cell budded off
Attachment proteins allow it to bind to host cell
How does a person with HIV develop AIDS and die of secondary infections
High viral load leads to increased destruction of T helper cells
Less activation of B cells
Less production of antibodies
Less able to destroy other microorganisms or abnormal body cells
How do antibodies contribute to a positive ELISA
First antibody binds to complementary antigen
Second antibody with enzyme attached is added
Second antibody attaches to antigen
Substrate added causing a colour change
Prophase
Nuclear membrane begins to break down
Centrioles move to opposite poles of cell
Chromatin supercoils and condenses into chromosomes
Metaphase
Spindle fibres form
Spindle fibres attach to centromere of chromosomes
Chromosomes align along the equator
Anaphase
Spindle fibres contract and shorten
Centromere splits
Sister chromatids are separated
Chromatids pulled to opposite poles of cell
Telophase
Nuclear membrane begins to reform
Chromosomes unwind
Homologous pair
Two chromosomes carrying the same genes in the same loci
How to make a mitotic index accurate
Repeat count to ensure figures are correct
Large number of fields of view so representative
Only count cells half or more in view to standardise counting
How does meiosis result in haploid chromosome number and show genetic variation
Homologous chromosomes pair up
Maternal and paternal chromosomes are arranged in any order
Independant segregation
Crossing over
Equal lengths of non sister chromatids exchanged between chromosomes
Producing recombinant alleles/new combinations
Chromatids separated at meiosis ll
What is crossing over and how does it increases genetic diversity
Homologous pairs of chromosomes associate and for a bivalent
Chiasmata forms
Equal lengths of non sister chromatids exchanged
Producing new combinations of alleles
Mitosis vs Meiosis
Mitosis is one division, meiosis is two
Mitosis produces genetically identical daughter cells whereas meiosis is genetically different
Two produced in mitosis whereas four in meiosis
Diploid to diploid in mitosis, diploid to haploid in meiosis
Crossing over only in meiosis
Independant segregation only in meiosis
Exon
Base/nucleotide/triplet sequence coding for a polypeptide of amino acids
Transcription in eukaryotes
Hydrogen bonds between DNA bases are broken by DNA helicase
Only one strand acts as a template
Free RNA nucleotides attracted to complementary base pair
Uracil with Adenine and Cytosine with Guanine
RNA polymerase joins adjacent RNA nucleotides
By phosphodiester bonds
Pre-mRNA is spliced to form mRNA and introns removed
Describe translation
mRNA attaches to ribosome
Moves along to find the start codon
tRNA anticodons bind to complementary mRNA codons
tRNA brings the specific amino acid
Which are joined by peptide bonds with energy from ATP
tRNA released after amino acid added to polypeptide
Ribosome moves along the mRNA and forms the polypeptide until reaches the stop codon
Ribosome can read two codons at once
Differences between mRNA and tRNA
mRNA has no hydrogen bonds but tRNA does mRNA linear tRNA clover leaf mRNA has no amino acid binding site tRNA does mRNA has more nucleotides tRNA are all similar length, mRNA varies mRNA has codons, tRNA has anticodons
Degenerate code meaning
More than one codon codes for an amino
Non overlapping meaning
A base from one triplet cannot be used in an adjacent triplet
How can a mutation in DNA base sequence lead to a non functional enzyme
Change in DNA base sequence
Change in primary structure/amino acid sequence
Change in hydrogen, ionic and disulphide bonding
Change in tertiary structure
Change in active site
No longer complementary to substrate so cant form an ESC
Two reasons why not all mutations cause a change
Triplets code for the same amino acid
Occurs in non coding sequence/intron
Phylogenetic group
Grouped according to evolutionary links/history
Hierarchy
Groups within groups
No overlap between groups
Genetic diversity
Differences in DNA base sequence/alleles of a population
Why is index of biodiversity better
Some species may be present in high or low numbers
Also measures the number of individuals in each species
How can comparisons of biological molecules be used to find out if closely related
Genetic variation; compare DNA base sequence/compare mRNA base sequence/compare sequence of amino acids
DNA hybridisation by separating strands of DNA; mix DNA strands of different species/heat required to separate strands indicates relationship
Immunological evidence; Inject x1 protein into x2/obtain antibodies/add protein from x2/amount of precipitate indicates relationship
Why is it better to classify from base sequence of gene than amino acid sequence of a gene
There are more bases than amino acids and base sequence is longer
Introns present in DNA but aren’t expressed in amino acids
Same amino acid can be coded for by different triplet due to degenerate DNA code
Describe the process that leads to a reduction in genetic diversity
Reduced number of different alleles/reduced gene pool
Founder affect
A few individuals from a population become isolated
Genetic bottle necks
Significant fall in size of population
Selective breeding and artificial selection
Using organisms with particular alleles/phenotypes
How can protein structure be used to investigate evolutionary relationship between species
Amino acid sequence
Is coded for by DNA base sequence
Closer amino acid sequence means closer relationship
Why does species diversity decrease when forests are cleared to make land available for agriculture
Decreased variety of plants and fewer species
Fewer niches/habitats
Decrease in variety of food/fewer food sources
Machinery and pesticides cause harm to organisms that were present
Pesticides kill species
Genetic bottle neck
Sudden decrease in population/many killed by an event like earthquake
Reducing genetic variation
Ethical arguments for maintaining biodiversity
Prevents extinction
Save organisms for future generations
Economic arguments for maintaining biodiversity
Medical/pharmaceutical uses Commercial products like wool Tourism Agriculture Saving local forest communities
How can clearing forests lead to reduced diversity of insects
Lower diversity of plants so fewer plant species
Fewer sources of food
Fewer habitats/niches
Pesticides and insecticides kill insects
How does courtship increase probability of successfully mating
Attracts mate of same species Attracts mate of opposite sex Indication of fertility/sexual maturity Stimulates release of gametes Form pair bond
Considerations for mark release recapture
No change in population size (no births, deaths, migration or emigration)
Markings should not make animals more susceptible to predators
Markings should not rub off or be lost
Sufficient time for fully dispersing through rest of population
Measure wind speed, soil pH, temperature and light intensity
Anemometer
pH probe
Digital thermometer
Lux meter
