B2 Flashcards
nucleotide structure
pentose sugar
phosphate group
nitrogenous organic bases
how are nucleotides joined
condensation reaction
phosphodiester bond (covalent)
mononucleotide–>dinucleotide–>polynucleotide
RNA structure
ribose pentose sugar
A, U, G, C
RNA uses
- mrna: synthesised in transcription- transfers genetic info from nucleus - cytoplasm + ribosomes
- trna: bring amino acids to ribosome complementary to mrna codon to form polypeptide in protein synthesis
- ribosomes = made of protein + rna
DNA structure
pentose sugar = deoxyribose
A, T, G, C
two strands = antiparallel
double helix
hydrogen bonds between complementary base pairs
phosphodiester bonds joining nucleotides together
stability of DNA
- phosphodiester backbone protects the more chemicallly reactive organic bases inside double helix
- hydrogen bonds link organic bases
3 hydrogen bonds between cytosine and guanine- more of these…more stable
function of DNA
hereditary molecule responsible for passing genetic information from cell to cell and generation to generation
how is DNA adapted to carry out its functions
very stable structure- passes between generations without significant changes
2 separate strands = joined with weak hydrogen bonds, allows them to separate during DNA replication and protein synthesis
extremely large molecule- carries immense amount of info
base pairing- DNA is able to replicate easily and transfer info as mRNA
4 different nitrogenous bases- ability to code information
each strand acts as a template at the same time
2 main stages of cell division
nuclear division
- can be mitosis or meiosis
cytokinesis
- followed by nuclear division- whole cell divides
why must DNA be replicated before a cell divides
to ensure all daughter cells have the genetic information to produce the enzymes and other proteins they need
requirements for semi-conservative replication
- 4 types of nucleotide
- both DNA strands to act as template
- DNA polymerase
- source of chemical energy
- hydrogen bonds
how the structure of DNA enables semi conservative replication
- double stranded
- weak hydrogen bonds
- complementary bases
DNA replication
- DNA helicase unwinds the double helix
- hydrogen bonds between complementary bases = broken
- each strand acts as a template
- new/free nucleotides form complementary base pairs
- A+T, G+C
- DNA polymerase forms covalent bonds between pentose and phosphate
forms phosphodiester bonds between nucleotides - process continues along entire molecule
conservative model of DNA replication
- the original DNA molecule remains intact
- a separate daughter DNA copy is built from new molecules of deoxyribose, phosphate and organic bases
- of the 2 molecules produced, 1= entirely new and 1= entirely original
semi-conservative model of DNA replication
- original DNA molecule = split into two separate strands
- each strand replicates w complementary base pairing
- each of the 2 new molecules has 1 original and 1 new strand
why is the direction of DNA polymerase in opposite directions?
- DNA has antiparallel strands
- the shape of adjacent nucleotides are different
- enzymes have an active site with a specific shape
- only substrates with a complementary shape will bind to the active site of DNA polymerase
structure of ATP
a phosphorylated macromolecule
- adenine: nitrogenous organic base
- ribose: pentose sugar that acts as a backbone
- phosphates: chain of 3 phosphate groups
how ATP stores energy
- bonds between phosphate groups = unstable w/ low activation energy so easily broken
when they do break, they release lots of energy
ATP + H2O –> ADP +Pi + (energy released for use by cells)
- catalysed by ATP hydrolase (ATPase) in hydrolysis
- exothermic
synthesis of ADP
energy = used to add an inorganic phosphate to ADP to re-form ATP
ADP + Pi + (energy supplied from respiration) –> ATP + H2O
- catalysed by ATP synthase
- condensation
- endothermic
the 3 ways in which synthesis of ATP occurs
- photophosphorylation
in chlorophyll-containing plant cells during photosynthesis
energy = from sunlight - oxidative phosphorylation
in plant and animal cells during respiration
energy = from electrons from oxidising of glucose - substrate-level phosphorylation
in plant and animal cells when phosphate groups are transferred from donor molecules to ADP
by enzymes
roles of ATP
good energy donor- not a good long term energy store
–> due to instability of its phosphate bonds
- immediate energy source of cell
so cells don’t store large quantities of ATP , just a few seconds supply
but it can be rapidly made again
why is ATP a better immediate energy source than glucose
energy = released in smaller, manageable amounts
hydrolysis = single reaction that releases immediate energy
phosphorylates other molecules, lowering their activation energy
ATP is useful in many biological processes. explain why
- releases energy in small/manageable amounts
- broken down in one step
- immediate energy source so energy = readily available
- phosphorylates other compounds
- lowering their activation energy, making them more reactive
- can be reformed/ made again
why do we need to make ATP continuously
ATP cannot be stored
it can move around a cell freely (it is soluble)
cannot cross the cell membrane- polar + no protein carriers
has to be continuously made within the mitochondria of cells that need it
why can ATP not cross the cell membrane
it is polar
it has no protein carriers
uses of ATP
a METABOLITE
provides the energy in metabolic processes needed to build up macro-molecules from their basic units
MOVEMENT
provides the energy for muscle contraction
for muscle filaments to slide past each other and so shorten the overall length of the muscle fibre
ACTIVE TRANSPORT
provides the energy needed to change the shape of carrier proteins in plasma membranes so molecules/ ions can move against a concentration gradient
SECRETION
needed to form the lysosomes necessary for secretion of cell products
ACTIVATION OF MOLECULES
the inorganic phosphate released during hydrolysis of ATP can be used to phosphorylate other compounds to make them more reactive, lowering their activation energy in enzyme-catalysed reactions
describe how an ATP molecule is formed from its component molecules
adenine, ribose sugar, 3 phosphates
joined by condensation reaction
by ATP synthase
during respiration / photosynthesis
give two ways in which the hydrolysis of ATP is used in cells
phosphorylates other molecules to make them more reactive
releases energy during respiration
the dipolar water molecule
O has 8-
H has 8+
dipolar
forms hydrogen bonds
causes water molecules to stick together
high specific heat capacity of water
because water molecules stick together, it takes more energy to separate them
so bp is higher than expected
it takes more energy to heat a given mass of water
water therefore acts as a buffer against sudden temperature changes,
making the aquatic environment a temperature-stable one
high latent heat of variation
hydrogen bonding between water molecules means it requires lots of energy to evaporate 1g of water
evaporation of water such as sweat in mammals is therefore a very effective means of cooling because body heat is used to evaporate the water.
cohesion and surface tension in water
cohesion: the tendency of water molecules to stick together
- with its hydrogen bonding, water has large cohesive forces that allow it to be pulled up through a tube e.g. xylem in transpiration stream
- in the same way, where water molecules meet air they tend to be pulled back into the body of water rather than escaping from it
at an air-water surface, the cohesion between water molecules produces surface tension, creating a solid-like surface
water in metabolism
- water is used to break down many complex molecules by hydrolysis e.g. proteins to amino acids
- water is also produced in condensation reactions
- chemical reactions take place in an aqueous medium
- water is a major raw material in photosynthesis
water as a solvent
water readily dissolves other substances:
- gases e.g. O2 CO2
- waste e.g. ammonia and urea
- inorganic ions and small hydrophillic molecules e.g. amino acids, monosaccharides, ATP
- enzymes, whose reactions take place in solution
other important features of water
its evaporation cools organisms and allows them to control their temperature
it is not easily compressed, so provides support e.g. hydrostatic skeleton of earthwork and turgor pressure in plants
it is transparent and therefore aquatic plants can photosynthesise
light rays can penetrate the jelly-like fluid that fills the eye and so reach the retina
where are inorganic ions found
in solution in the cytoplasm of cells
in bodily fluids
part of larger molecules
role of iron ions
found in haemoglobin, play a role in transport of O2
role of phosphate ions
form a structural role in DNA
store energy in ATP
structural in phospholipid bilayer
role of H+
determine the pH of solutions
and therefore the functioning of enzymes
role of Na+
important in transport of glucose and amino acids across plasma membranes
Na K pump
roles of NH3
amino acids
nitrogenous bases
role of Ca+
muscle contraction
explain the properties of water that make it important for organisms
METABOLITE
in condensation/hydrolysis/photosynthesis/respiration
SOLVENT
a universal solvent- only for polar substances
so metabolic reactions can occur
HIGH SPECIFIC HEAT CAPACITY
so temperature buffer
LARGE LATENT HEAT OF VAPORISATION
providing cooling effect through evaporation
COHESION BETWEEN WATER MOLECULES
so provides support to columns of water in plants
COHESION between water molecules
produces surface tension, supporting small organisms
properties of water that are important in the cytoplasm of cells
polar molecule
acts as a universal solvent
metabolic reactions occur faster in solution
very reactive
metabolic reactions occur efficiently
temperature buffer- high specific heat capacity
maintains optimum temp for enzymes
describe the structure of DNA (5)
- a polynucleotide
- each nucleotide formed from deoxyribose, phosphate group, and nitrogenous base
- phosphodiester bond between nucleotides
- double helix structure
- hydrogen bonding between adenine + thymine and guanine + cytosine
describe how a phosphodiester bond is formed between two nucleotides (3)
- condensation reaction
- between phosphate and deoxyribose
- catalysed by DNA polymerase
describe the role of DNA polymerase in the semi-conservative replication of DNA (3)
- joins adjacent DNA nucleotides
- catalyses condensation reactions
- catalyses the formation of phosphodiester bonds between adjacent nucleotides.
describe the role of two named enzymes in the process of semi-conservative DNA replication
DNA helicase
causes breaking of hydrogen bonds between bases on DNA strands
DNA polymerase
joins DNA nucleotides forming phosphodiester bonds
describe the role of iron, sodium and phosphate ions in cells
iron
haemoglobin binds with O2 in RBC
sodium
co-transport of glucose/amino acids
because sodium moves out by active transport by Na-K pump
creates a concentration gradient
phosphate
used to produce ATP
phosphorylates other compounds, making them more reactive
part of phospholipid bilayer
