Model Answers Flashcards
Binary fission
• Bacteria an prokaryotes reproduce by binary fission
• First the DNA (and plasmids) are replicated
• Then the cytoplasm and cell membrane divides in two
• Each daughter receives on copy of the circular DNA (and variable number of plasmids if present)
Lipid absorption
• Micelles contain bile salts and fatty acids/monoglycerides, making them soluble in water.
• Fatty acids/monoglycerides are released to cell/lining of the ileum.
• This maintains a higher concentration of fatty acids/monoglycerides outside the cell, so they are absorbed by simple diffusion.
• Triglycerides are reformed in cells and form chylomicrons.
• The chylomicron vesicles fuse with the cell membrane and are released by exocytosis
Cardiac cycle lhs
• Blood arrives at the left atrium from the pulmonary vein filling the atrium increasing the pressure.
• The atrial muscle contracts increasing the pressure in the atrium until it is greater than the ventricle – this forces the blood through the atrioventricular valve into the left ventricle.
• The increase in pressure of the ventricle closes the atrioventricular valve, preventing back flow of blood.
• Then the left ventricle muscle contracts increasing the pressure until it is greater than in the aorta, this forces the blood through the semilunar valve.
• The pressure in the aorta increases causing the semilunar valve to close preventing back flow
Starch digestion
• Amylase in saliva hydrolyses starch (by breaking the glycosidic bond) to maltose (alpha glucose disaccharide)
• Amylase is denatured in the stomach – no carb digestion there
• Pancreatic amylase is released and further hydrolyses any leftover
starch
• Maltose is hydrolysed to α-glucose by breaking the glycosidic bond in the ileum by the enzyme maltase which is a membrane-bound enzyme
• Glucose is absorbed in co-transport
Protein digestion
• Hydrolysis of peptide bonds.
• Endopeptidase act in the middle of protein/polypeptide in the stomach and produces shorter polypeptides, increasing the number of ends
• Exopeptidases act at end of protein/polypeptide and in the stomach and produce dipeptides.
• Dipeptidases are membrane bound enzymes in the ileum which act on dipeptides and produce single amino acids
Lipid digestion
• Bile salts emulsify lipids into micelles to increase surface area and solubility in water
• Lipids/triglycerides are hydrolysed by lipases to form fatty acids and monoglycerides
• Micelles contain fatty acids, monoglycerides and bile salts
• They move through the ileum to the epithelium cells
Cardiac cycle rhs
• Blood arrives at the right atrium from the vena cava filling the atrium increasing the pressure.
• The atrial muscle contracts increasing the pressure in the atrium until it is greater than the ventricle – this forces the blood through the atrioventricular valve into the right ventricle.
• The increase in pressure of the ventricle closes the atrioventricular valve, preventing back flow of blood.
• Then the right ventricle muscle contracts increasing the pressure until it is greater than in the pulmonary artery, this forces the blood through the semilunar valve.
• The pressure in the right pulmonary artery increases causing the semilunar valve to close preventing back flow.
Mitosis
• DNA is replicated in S-phase of interphase
• Prophase – Chromosomes condense and become visible, nuclear
membrane dissolves
• Metaphase – Chromosomes line up at the middle of the cell
• Anaphase – Sister chromatids are pulled to the opposite poles of the cell
• Telophase – Chromosomes decondense and the nuclear envelope starts to reform around the two nuclei
• Cytokinesis – The cytoplasm and surface membrane splits forming two new cells that are genetically identical
Meiosis
• DNA is replicated in interphase before meiosis begins
• In the first division there is a separation of homologous
chromosomes, halving the chromosome number
• In the second division there is separation of the sister chromatids • This produced four genetically different daughter cells
Genetic variation
• Mutations can occur changing the base sequence leading to the formation of new alleles
• In the first division of meiosis there is crossing over where homologous chromosomes swap DNA producing new combinations of alleles
• In meiosis homologous chromosomes may be independently segregated, separating into different daughter cells producing new combinations of alleles
• During fertilisation there is random fusion of gametes this produces new combinations of alleles
Transpiration
• Waterevaporatesfromtheleaves/transpiration
• Duetoheat/kineticenergyfromsunlight
• Waterdiffusesoutofthestomatafromahighwaterpotentialtolow
• The diffusion of water causes a negative hydrostatic pressure in the xylem
• Thisisduetowaterpotentialgradient
• Cohesiontensionformsacontinuouscolumnofwaterthatispulled
through the xylem in a transpiration stream
•Water’sadhesivepropertiesaidthemovementthroughthexylem
• Transpirationstreamlowerswaterpotentialintherootcells
• Waterisabsorbedthroughtheroothaircellsbyosmosisfromahigher water potential to low.
Factors affecting transpiration
• Humidity – increases or decreases the water potential gradient
• Light intensity/stomata opening/no of stomata – more light more
photosynthesise, stomata open in the day close at night
• Temperature – increases kinetic energy, more diffusion
• Wind movement - increases or decreases the water potential gradient
Translocation/mass flow
• Sucrose (and other solutes) are actively transported into phloem (or co-transported with H+) by companion cells
• This lowers the water potential in the phloem and water moves in by osmosis
• This creates high hydrostatic pressure leading to mass flow to respiring cells/storage organs
• Solutes/sucrose is unloaded from the phloem by active transport
Protein structure
• Proteins have a primary structure that is formed by a sequence of many amino acids that are joined by peptide bonds in a condensation reaction
• The primary structure folds into a secondary structure of either alpha helix or beta pleated sheets and these are held together by hydrogen bonds
• The secondary structure further folds into a tertiary 3D structure that is held together by hydrogen bonds, ionic bonds and disulphide bonds
• Some proteins e.g. antibodies may form a quaternary structure of more than one polypeptide chain(some of these may have prosthetic groups e.g. haem)
DNA structure
• DNA is made of a polymer of nucleotides/polynucleotide
• It is two molecules that are antiparallel to each other coiled into a double
helix.
• Each nucleotide is made of deoxyribose, a phosphate group and a nitrogenous base that can either be adenine, cytosine, thymine or guanine
• The adjacent nucleotides are joined to each other between the sugar and phosphate groups in a condensation reaction forming a phosphodiester bond
• Complementary base pairing holds the two strands together due to hydrogen bonds forming between A - T and C - G.
Chromosome structure
• Chromosomes are wrapped around histone proteins forming a nucleosome
• Replicated chromosomes are formed of two sister chromatids attached at the centre by a centromere
Comparison of prokaryote and Eukaryote DNA
• Prokaryote DNA is short Eukaryote DNA is long
• Prokaryote DNS is circular Eukaryote DNA is linear
• Prokaryote DNA has no introns Eukaryote DNA has introns
• Prokaryote DNA is free floating Eukaryote DNA is in in the nucleus (and mitochondria and chloroplasts)
Splicing
• Eukaryotic DNA forms pre-mRNA when transcribed
• Pre-mRNA contains introns (non-coding DNA) this must be spliced out • Pre-mRNA is spliced and introns are removed
• Mature mRNA is transcribed
Splicing
• Eukaryotic DNA forms pre-mRNA when transcribed
• Pre-mRNA contains introns (non-coding DNA) this must be spliced out • Pre-mRNA is spliced and introns are removed
• Mature mRNA is transcribed
ATP structure
• ATP has a nucleotide structure
• It is a ribose sugar with adenine base and three phosphates groups
attached to it
• These phosphate groups can be hydrolysed to remove one phosphate
• This hydrolysis can be used to release energy for chemical reactions, but can also be used in phosphorylation which can make substrates more reactive
DNA replication
DNA helicase breaks the hydrogen bonds causing the strands to separate
Both strands act as a template
Free nucleotides complementary base pair to the template A-T and G-C
DNA polymerase joins adjacent nucleotides together forming a phosphodiester bond
Hydrogen bonds form between the old strand and the newly synthesised strand
DNA replication is semi-conservative replication
Transcription
• DNA strands are separated by breaking hydrogen bonds
• Transcription is the synthesis of an mRNA copy of a gene;
• The copy is complementary to the DNA template/antisense strand;
• RNA polymerase attaches to DNA
• RNA nucleotides matched to exposed complementary bases;
• Adjacent nucleotides are joined by a phosphodiester bond together to make a strand of mRNA;
• mRNA molecule separates from DNA
• In eukaryotes only: mRNA is spliced to remove introns
• Mature mRNA leaves the nucleus through nuclear pores
Translation
• mRNA attaches to the ribosome at a start codon
• tRNA with a complementary anticodon attaches to the mRNA codon
• This tRNA is attached to a specific amino acid
• Amino Acids are joined by a peptide bond
• Using energy from ATP
• tRNA is released from the ribosome and a new on enters
• Ribosome moves along the mRNA to synthesise a complete polypeptide
How DNA codes for proteins
• DNA has a specific sequence of bases where a triplet of three bases codes for a specific amino acid.
• The order of the triplets codes for a specific sequence of animo acids of a polypeptide/primary structure