Res 2 flashcards
What is osmosis
the net movement of water from an area of high water potential to lower water potential through a semi-permeable membrane, until equilibrium
what is water potential
the concentration of water
what is the highest water potential
0
what happens when there is more solute in water
water potential decreases
describe the characteristics of osmosis
passive process- no ATP required
continues until equilibrium
follows movement of solute as water potential decreases
therefore random movement of particles
what happens when animal cell has low water potential and outside has high water potential
water enters the cell plasma membrane can’t stretch so cell bursts/cytolyses
what happens when plant cell has lower water potential and outside has higher water potential
water enters the cell plasma membrane is surrounded by cell wall therefore the cell becomes turgid
what happens when there is a higher water potential inside animal cell
water leaves the cell so cell shrives
what happens when theres a higher water potential in plant cell
water leaves and cell becomes plasmolysed
what is plasmolysis
when plasma membrane comes away from cell wall
when is something flaccid
when all cells in a tissue are plasmolysed
What is the semi-conservative model for DNA replication
New DNA molecules made up of 1 new and 1 original strand
How is DNA replicated
DNA helicase unzips the DNA by breaking the hydrogen bonds
this seperates the DNA molecule into 2 template strands
Activated nucleotides join by complementary base pairing to the 2 template strands
Hydrogen bonds form between free nucleotides and each template strands
DNA polymerase joins sugar phosphate backbone by forming phosphodiesther bonds between nucleotides
Semi conservative model: new DNA molecules made up of 1 new and 1 original strand
Each molecule forms a double helix
How’s does DNA’s structure allow replication
Double stranded- each strand acts as a template
H-bonds- easily broken
Base pairing- complementary bases hold strands together
How was the Messelson-Stahl experiment carried out
They grew E-coli on nitrogen15- all of ther DNA was nitrogen15
They then transferred bacteria to nitrogen14 substrate
This means that DNA replications from now on can only use Nitrogen14
Using centrifugation, the DNA from each subsequent replication can be seperated
The band pattern reveals the mechanism
What is the conservative model for DNA replication
One of daughter molecules ends up with new DNA and other molecule ends up with old
What is the Dispersive model of DNA replication
Daughter DNA molecules made up of part new molecule and part original strand (hybrid)
When does DNA replication occur?
synthesis phase of cell cycle
what happens after DNA replication
mitosis
what are the monomers of DNA
nucleotides
How do nucleotides join
By a bond between Phosphate group of one molcule and pentose sugar of other molecule
What is the name of the bond that joins nucleotides
phosphodiesther bond
What are the bases of DNA
Adenine
Thyamine
Guanine
Cytosine
What are the bases of RNA
Adenine
Uracil
Cytosine
Guanine
What are the bases of RNA
Adenine
Uracil
Cytosine
Guanine
What is the structure of RNA
smaller than DNA less stable than DNA single stranded ribose sugar AUCG
What is the structure of DNA
Double stranded
Complementary base pairs
Hydrogen bonds between bases
Forms ‘double helix’
How does the structure of DNA relate to its function
very long molecule means holds alot of information
double stranded means both strands used as templates in replication
helix means compact
sugar phosphate backbone provides chemical and physical protection of bases
weak hydrogen bonds means molecule easily broken for replication
strong hydrogen bonds means stable molecule
base sequence codes for primary structure of proteins
What does ATP stand for
adenosine triphosphate
How is ATP synthesised
ADP and inorganic phosphate react to make ATP. It’s a condensation reaction and the enzyme involved is ATP synthase.
How is ATP broken down
ATP reacts to form ADP and inorganic phosphate. This is a hydrolysis reaction which means energy is released and the enzyme involved is ATP hydrolase.
Why is ATP so useful as a molecule
single bond broken
therefore immediate energy release
small/manageable amount of energy release
Rapid synthesis as only a single bond is formed
soluble so diffuses around cell easily
What is an antigen
A foreign protein which stimulates an immune response
what is an antibody
A protein specific to an antigen and secreted by plasma cells
What is the humoral response
B cells and antibody secretion
What is the structure of antibodies
quartenary structure with two heavy polypeptide chains bonded by disulfide bonds to two light polypeptide chains
what does each polypeptide chain consist of
constant region and variable region
What does the constant region determine
the mechanism used to destroy pathogens
What is the variable region
amino acid sequence (at tip of Y) and where the antibody attaches to the antigen to form an antigen-antibody complex
what is the difference between active immunity and passive immunity
Active is when antigen required, B memory cells produced, long term immunity and takes a long time whereas Passive immunity doesnt require antigen, no B memory cells produced, short term immunity and Immediate immunity
how do you increase rate of diffusion
increase surface area
increase concentration gradient
decrease diffusion pathway
how is gas exchange maximised in fish
many lamellae= high sa
each lamellae v thin= short diffusion pathway
countercurrent flow= maintains steep conc gradient across whole length of lamellae
blood oxygen conc always greater than water oxygen conc
ventilation replaces o2 depleted water
blood circulation replaces o2 rich blood
what is the counter current flow and how does it maximise gas exchange
water flows in one direction over gills and blood flows in opposite direction over lamellae
this results in highest o2 conc at one end and lowest o2 conc at other end
because of counter current flow o2 conc in water always higher than o2 conc in blood
therefore diffusion occurs across whole length of lamellae
therefore gas exchange maximised
how does fish ventilate
mouth opens
bucal cavity volume increases therefore pressure decreases
mouth closes
buccal cavity volume decreases therefore pressure increases
causing operculum to open and water to flow through gills
how is gas exchanged in insects
o2 diffuses down conc gradient from outside to cells
co2 diffuses out down its own conc gradient- independent of each other
how does the exoskeleton minimise water loss
hydrophobic hard waxy coating on outside of body
what happens during increased respiration rate in insects
Lactate produced in cells. Therefore creates difference in water potential. water absorbed by osmosis therefore increased surface area for gas exchange
how do spiracles prevent water loss
they close
