Year 12 Flashcards
Structure of DNA related to its function
Sugar-phosphate backbone so provides strength
Double helix so backbone protects bases
Helix so compact
Base sequence allows information to be stored
Double stranded so semi conservative replication occurs
Complementary bases so replication accurate
Hydrogen bonds easily broken for replication
Many hydrogen bonds so stable
DNA replication
Two strands so semi conservative replication possible
DNA helicase breaks hydrogen bonds between bases
Strands separate and both act as template
Free DNA nucleotides diffuse into position according to complementary base pairings
Hydrogen bonds hold nucleotides in place
DNA polymerase joins nucleotides together
To form phosphodiester bonds
DNA one parent and one new strand
Transcription
DNA helicase breaks hydrogen bonds between bases
Strands separate
One DNA strand acts as a template
Free RNA nucleotides diffuse into position according to complementary base parings
RNA polymerase joins RNA nucleotides together to for phosphodiester bonds
Pre-mRNA spliced to remove introns
Mature mRNA contains exons
Translation
mRNA leaves nucleus through nuclear pore to ribosome
tRNA molecules bring amino acids to ribosome
Specific tRNA molecule for specific amino acids
Anticodon of tRNA is complementary to codon on mRNA
Two amino acids held close together on ribosome
Peptide bond forms between amino acids
tRNA detaches and collects another amino acid from cytoplasm
Ribosome moves along mRNA
Mitosis
DNA replicated
Chromosomes condense or DNA wrapped around histones
Each chromosome has 2 identical chromatides due to replication
Chromosomes move to equator of cell
Centromere attach to individual spindle fibres
Spindle fibres contract
Chromotides separate and move to opposite poles
Nuclear envelop forms around each group of chromosomes
Cytokinesis
Meiosis
DNA replicates
Chromosomes condense
Chromosomes associate in homologous pairs or bivalents
Crossing over takes place
Centromeresjoin to spindle at equator of cell
Homologous chromosomes move to opposite poles
Cytokinesis
Chromosomes move to equator
Centromere attach to spindles
Chromotides move to opposite poles
Cytokinesis
Sources of variation
Mutation
Caused by mutagenic agent
Change in base sequence
Deletion/substitution
New protein coded for
Crossing over
Different combination of alleles
Independent assortment of homologous chromosomes in meiosis I and II
Random fusion of gametes at fertilisation
New combination of alleles
Isolation of cell organelles
Cell homogenisation to break open cells
Filter to remove whole cells
Use isotonic solution to prevent osmotic damage to organelles
Cold to prevent damage by enzymes
Buffer prevent protein and enzyme denaturing
Centrifuge at lower speed to separate nuclei
Re-spin supernant at higher speed
Mitochondria in pellet
Re-spin supernant at higher speed
Ribosome pellet
Diffusion
Movement down concentration gradient
Small, non polar molecules pass through phospholipids
Large, polar molecules go through channel/carrier proteins- facilitated diffusion
Osmosis
Water moves by osmosis from high water potential to low water potential through channel proteins. Partially permeable membrane
Active transport
Movement against the concentration gradient
Uses specific carrier proteins
Requires ATP
Co-Transport of glucose
Glucose moves into epithelium cell with sodium ion
Using carrier protein
Sodium ions move down concentration gradient
Sodium ions actively transported out epithelium cell into blood
Potassium ions move in opposite direction
Maintaining low concentration of sodium ions in epithelium cell
Glucose diffuses into blood using protein
Structure of proteins
Polymer of amino acids
Joined by peptide bonds
Formed by condensation reaction
Primary structure is order of amino acids in the chain
Secondary structure is specific folding of polypeptide chain held by hydrogen bonds
Tertiary structure is 3-D folding of polypeptide chain held by hydrogen bonds, ionic and disulphide bonds
Quaternary structure is made of two or more polypeptide chains
ATP
Consists of Adenine, ribose and 3 phosphate groups
Releases energy in small manageable amounts
Hydrolysed in one step
Energy available rapidly
Used to phosphorylate molecules
Used to lower activation energy
Reformed by adding phosphate to ADP
Breathing out
Contraction of internal intercostal muscles Relaxation of external intercostal muscles Ribs to move down and in
Relaxation of diaphragm muscles Diaphragm to become domed
Decrease in volume of thorax Increase in pressure in thorax Air forced out of lungs
Breathing in
Relaxation of internal intercostal muscles Contraction of external intercostal muscles Ribs to move out and up
Contraction of diaphragm muscles Diaphragm to become flat
Increase in volume of thorax Decrease in pressure in thorax Air forced into lungs
Heart beat
Blood enters atrium
Atrium wall contracts
Increases pressure in atrium
Causes atrioventricular valves to open
Blood passes into ventricle
Ventricle contracts increasing pressure
Atrioventricular valve closes when pressure greater than atrium
When ventricle has higher pressure than aorta semilunar valve open
After contraction higher pressure in aorta than ventricle cause semilunar valve to close
Tissue fluid
Hydrostatic pressure of blood high at arterial end of capillary bed Due to contraction of left ventricle
Fluid (containing solutes) forced out of capillary wall
Proteins and large molecules remain in blood
Water potential of blood becomes more negative
Water moves back into venous end of capillary by osmosis Lymph system collects excess tissue fluid and returns to vein
Formation of oxyhemoglobin
Haemoglobin – a protein with a quaternary structure. Binds with oxygen to form oxyhaemoglobin
At lungs oxygen binds to haemoglobin
Difficult for first oxygen to bind.
Binding causes a change in the tertiary/quaternary structure of protein Exposes another oxygen binding site
Further oxygen molecules bind to haemoglobin more easily.
Bohr effect
Increased rate of respiration
Increase of carbon dioxide in blood.
Increase carbonic acid/decrease in pH.
Changes quaternary/tertiary structure of haemoglobin Oxygen dissociates more rapidly
Delivers more oxygen to respiring tissues.
Transpiration
Water evaporates from mesophyll cells in the leaf Water vapour diffuses out of leaf through stomata Water potential in leaf cells decreases
Water moves out of xylem into leaf cells
Creates a tension on the column of water in xylem
Water molecules joined by hydrogen bonds
Water molecules does not break because of adhesion with xylem walls Water enters root hair cells by osmosis
because active uptake of mineral ions has created a water potential gradient water moves through the root by osmosis to xylem
Translocation
At source sucrose is actively transported into the phloem. By companion cells
Lowers water potential in phloem
Water enters by osmosis
Produces high hydrostatic pressure
Mass transport towards sink
At sink sugars are removed
Sugar used in respiration or storage as starch
Phagocytosis
Phagocyte attracted to pathogen by chemicals or foreign antigen Engulfs pathogen
Bacteria in phagosome
Fuses with lysosome
Form phagolysosome Pathogen hydrolysed;
Humoral response
Pathogen with foreign antigen detected
Engulfed by phagocyte
Antigen attached to cell membrane of phagocyte (antigen presentation) Th cell with complementary receptor binds to antigen
Th cell stimulates B cell
Specific B cell activated
Divides to form clone (clonal selection)
By mitosis
Plasma cells produced
Release antibodies
Antibody specific to antigen
Antibody destroys cells with antigen
