138 Molecular And Cell Biology Flashcards
Give features that are present only in an animal cell
Centriole - organises spindle fibres for mitosis
Microvilli
Glycosome - stores glucose
Lysosome
Give features of plant cells that arent present in animal cells
Plasmodesmata
Large vacuole
Chloroplast
Cell wall
What is a peroxisome?
Organelle involved in catabolism of long chain fatty acids, amino acids and polyamines.
It can also reduce reactive oxygen species e.g. Hydrogen peroxide
Contains catalyses and oxidases.
Most significant differences between eukaryotes and prokaryotes
Membrane bound organelles
Nucleus
How much of a cells volume is protein? What effect does this have on the inside of the cell?
20-30%
Very insoluble so a thick gel structure forms
Describe the effect of the mycorrhizal arbuscules in plants
Small fungi that penetrate root cells, they supply the plant with nitrogen, phosphorus, and sulphur. In return the fungus receives metabolites e.g. Glucose. A symbiotic relationship
What is meant by a coenocytic structure?
Very large cells that have more than one nucleus as well as an excess of other organelles.
Give a use of compartmentation in the mitochondria during oxidative phosphorylation
Inner membrane is pH7 the matrix is pH 7.5 this enables a proton gradient to be maintained - protons will move through ATP synthase
Give three general reasons for cell compartmentation
Enables sequestration of toxic compounds
Keeps enzymes and substrates separate
Keeps cell conditions optimum for the different activities within the cell
Describe microtubules
Cylindrical tubes made from tubulin
20-25 nanometers wide
Give three things that microtubules do
Determine cell shape
Form a trackway for organelles and vesicles to move along
Form spindle fibres for mitosis
Describe microfilaments
Actin fibre - 3-6 nanometers involved in muscles contraction
Describe intermediate filaments
8-12 nanometer and anchor the nucleus and give some flexibility
What is the cytoskeleton
A mixture of protein filaments (microtubules, microfilaments) and motor proteins that form a 3-D mesh that works to hold the rigidity of the cell
Which motor protein moves towards the positive side of the cell?
Kinesin
The positive side is away from the nucleus
Dynein moves towards which side of the cell?
The negative end of the cell, i.e towards the nucleus
What are melanosomes?
Vesicles containing melanocytes that can be moved through an organism. Enables it to change colour (melanocytes contain pigments)
What is the use of cortical microtubules?
They reinforce the cell cortex, their direction determines the direction in which the cell elongates.
What proportion of genes code for proteins that pass through the Golgi apparatus
1/3
What is protein translocation?
Occurs in the endoplasmic reticulum
- where a protein enters
- protein has an N - terminal amino acid sequence
- this is removed when the protein enters the ER
Give two modifications that may occur in the endoplasmic reticulum
Glycosylation
Disulphides bond formation
What is the role of the Golgi apparatus?
Distribution, shipping and manufacturing of a cells chemical products
Insulin is what type of hormone? Where is it released from?
Peptide hormones released from the pancreatic B cells (islets of langerhans)
What type of protein is mucus?
Glycoprotein
Casein is found in what? From where is it released?
Milk
Mammary gland
Describe the process of milk production
Smooth ER forms a lipid vesicle which it secretes into the cytoplasm
Rough ER synthesises casein
Casein packaged into vesicles and delivered via the Golgi
Lactose is synthesised from glucose within the golgi
What is the role of a protein body? Name one in plants
Store proteins to help aid rapid growth
Vacuole
How do protein bodies prevent the castor bean plant poisoning itself?
Castor Beans contain Ricin (lethal does in humans is 22micrograms per kilogram) Its an anti herbivory meaning it inhibits protein synthesis by binding irreversibly to eukaryotic ribosomes.
Made of two pro ricin chains (A and B) these are modified in the ER and have their N terminal sequence removed, they are now active. The Golgi apparatus glycosaltes them and moves them to a protein body. Hence the active form is never present in the cytoplasm
Describe cystic fibrosis and how the endoplasmic reticulum causes cystic fibrosis
Cystic fibrosis is caused by a mutation in the chloride ABC (ATP binding cassette protein). This protein moves mucus from the lungs. Without it mucus accumulates = coughing and prevents enzymes from getting into the intestines.
Mutant chloride ABC usually has a mutation on the phenylalanine 508 protein, this doesn’t effect function but the endoplasmic reticulum sees the mistake and degrades the protein.
How does the ER degrade mistaken proteins
Lysosomes and proteasome move in with degrading enzymes
What is the role of chaperones in the ER?
They try to prevent mutation of proteins, work to assist the intracellular folding of proteins
Give some roles of lysosomes
Recycle misfolded proteins
Storage of carbohydrates organic acids
Store toxic substances
Describe how cyanide doesnt kill the plants in which its made
You need a cyanogenjd glucoside (dhurrin) this is sequestered in a vacuole.
You also need glucosidases (enzymes that activate it)
The two need to mix, this only occurs where a vacuole is ruptured i.e. When bitten into.
Give evidence from: DNA, replication, ribosome size, size, porins and initiating amino acid for the endosymbiotic theory
Prokaryotes, mitochondria and chloroplast all have 1 single cicrular chromome eukaryotes hafe linear chromomes
” replicate by binary fission, eukaryotes by mitosis
“ have 70s ribosomes, eukaryotes have 80s
“ are 1-10ym whilst eukaryotes are 50-500ym
“ have porins eukaryotes don’t
“ initiating amino acid is N-formymethionine, eukaryotes this is methionine
How has peptidoglycan helped provide evidence for endosymbiotic theory?
Make cell walls in cyanobacteria, genes for this still present in arabidopsis
How has cardiolipin provided evidence for endosymbiosis?
Constitutes 20% of mitochondrial inner membrane, but is only present elsewhere in bacteria
Describe a piece of living evidence for endosymbiosis involving sea slugs
Sea slugs eat seaweed and injest the chloroplasts which they can store on their backs. They can live without food for sometime after this, the chloroplasts are providing energy.
How many genes in arabidopsis have been transferred from cyanobacteria?
4500
mtDNA codes for what?
rRNA, tRNA and components for oxidative phosphorylation
Why is mtDNA inheritance very maternal?
1) egg cell far bigger: can contain up to 1 million mtDNA molecules, smaller sperm cell has at most 1000
2) then when fertilisation occurs the mitochondria within soerm are degraded anyway
3) some male mtDNA wont even reach the egg anyway
Describe the construction of rubisco
Has 8 large subunits made in the chloroplast on 70s ribosomes
And 8 small subunits made in the cytoplasm on 80s chromomes
The small unit has a signal sequence to enter the chloroplast which is removed on entry
Chaperones aid the assembly of the subunits pieces
Describe plastid diversity (i.e. Its “phylogeny”)
Protoplastid - early in development
This develops into either a chloroplast or leucoplast (in dark conditions an etioplast)
Green cholorplast can change into a red chromoplast (green vs red peppers)
Leucoplast contain no pigment and store biological molecules wothin them: amyloplast store sugars; elaioplast store oils ; proteinoplast stores protein
Give an example of a plant without any plastid genes, why dpesnt it need them?
Rafflesia lagascae (the biggest plant - red) Because it is parasitic it doesnt need photosynthesis
What are apicomplexia? Give an example and the disease it causes
Parasitic single celled eukartotic organisms that are derived from red algae. Their apicoplast ( a plastid) enables their parasitic nature.
E.g. Plasmodium that causes malaria
Why are the genomes of of individual organelles advantageous?
Having a genome is inexpensive (2% of cells energy budget)
Making proteins is very expensive (75% of cell budget)
Mitochondrial genes enable oxidative phosphorylation which increases the budget, hence creates a 200,000 fold rise in genome size in eukaryotes as opposed to prokaryotes
Give a brief timeline of DNA discovery
1874 - Friedrich misescher finds the chemical compositions of DNA through nuclein tissue extracts
1881 - Albert Kossel isolated the nucleotide bases
1953 - molecular structure of DNA resolved by x ray crystallography by Rosalind franklin
Watson and crick deduce helical structure and the spacing of the nucleotide bases
Which bases are the purines ?
Adenine and guanine
Thymine, cytosine and uracil make up what group of DNA bases?
Pyrimidines
How many hydrogen bonds form between A and T
2
Which base pairs form 3 hydrogen bonds between them?
G and C
Nucleotides are added to which end of DNA backbone? Why?
3’ end
Reaction occurs between one of three phosphates on nucleoside (nucloside has 3 phosphates which are removed to become a nucleotide) i.e. The nucleotide binds to the sugar
Is replication faster in prokaryotes or eukaryotes
Prokaryotes
Where does replication start? How many of these are there in a prokaryote?
At the origin of replication - determined by a sequence of bases
There is one in prokaryotes
Describe the replication of prokaryotic DNA (leave lagging strand synthesis)
1) unwinds - DNA helicase bind at start of the replication fork and untwist the helix. Isotopomerase deals with overwinding, breaks DNA and swivels it around and rejoins.
2) single stranded binding proteins bind to the DNA to stabilise it.
3) primase synthesises short RNA primers using parental DNA as a template (5-10 base pairs long)
4) new bases are added at the 3’ end. DNA polymerase binds to the end of the primer with a sliding clamp protein attached anchoring the polymerase to the leading strand. Chain moves through the clamp polymerase complex whilst it itself is still adding bases on
Describe the process of synthesising the lagging strand of DNA
Periodic addition of DNA primers, to which polymerases attach
Polymerases synthesises between the primers
Polymerase 1 removes the primers and any gaps are filled in
Gaps formed are called Okazaki fragments, these are filled in by DNA ligase
The replication machinery REMAINS STATIONARY
Why do chromosomes get shorter through replication cycles? What can be done to reverse this
Nothing can be attached to the location of the first DNA primer, polymerase falls off at the other end before synthesising it all.
Telomeres counter this by being large sections of junk DNA, it has no effect if these are removed
Telomerase catalyses the replication of telomeres in germ cells
Describe how DNA is packed in prokaryotes
Supercoiled associated with small amounts of protein. Found in the nucleoid
Describe the packing of DNA in eukaryotes
Linear DNA associated with histones to make chromatin
Nucleosomes = first layer of packing
Nucleosomes interact with histone tails to form chromatin figres (30nm thick)
Fibre forms loop domains called domains attached to chromosomes to form a scaffold, fibre increased to 300 nm. Looped domains coil further until width is 700nm
Describe why transcription and translation are faster in prokaryotes
No nucleus therefore transcription and translation occur in the same place
Translation can therefore occur before transcription has finished
What is the main difference between prokaryotic and eukaryotic transcription?
In eukaryotes premRNA is formed which is spliced into mRNA (no premRNA in prokaryotes)
Describe the initiation step of transcription
RNA Polymerase binds to a promoter region (can be either side of the DNA)
Cannot do this directly - TATA boxes recognised by transcription factors, the factors bind
Facilitates binding of RNA polymerase