Pepsin is in a class of protease enzymes known as endopeptidases. This means that it cleaves proteins in the middle of the protein and not at the ends.
Explain why pepsin can only be an endopeptidase.
Protein structure
Proteins are polymers that are made of amino acid monomers, which are connected by peptide bonds.
How the ends of the protein differ
The ends of the protein do NOT have a peptide bond but instead, have an amino group on one end and a carboxyl group on the other.
Enzyme function
The active site of pepsin has a specific shape. The tertiary structure of the enzyme is complementary to a peptide bond between amino acids.
Conclusion
This means that the ends of the protein cannot fit in the active site. Only the middle of the protein can bind to the enzyme and form an enzyme-substrate complex.
why is insulin inject and not taken as a pill
.insulin is a protein
.protease enzyme in the stomach will denature the enzyme
.if some insulin does escape digestion it will be denatured by the low stomach PH
.It would also not be small enough to be absorbed into the small intestine tissue
.injecting into the blood stream would allow for insulin to be absorbed by muscle tissue
what produces amylase
salivary glands
pancreas
why is maltose only hydrolysed by maltase
specific enzyme active shape
due to tertiary structure
only maltose can bind to form enzyme substrate complex
why does the hydrolysis of lactose make milk sweeter
lactose is hydrolysed into glucose and galactose
more sugar molecules present
different receptors are stimulated, a sweeter taste is caused.
how does centrifuging a culture allowed cell free liquid to be obtained
dense cells and spun into pellets and sink to the bottom
liquid is separated
these can be removed separately
describe primary structure of all proteins
sequence of amino acids in the polypeptide chain of a protein joined by peptide bonds
what does it mean for DNA to be universal
same codon codes for the same amino acid
how does ATP synthases structure allow it to catalyse ATP synthasis
active site is complementary to ADP + Pi so enzyme substrate complexes form
how does ATP synthases structure help move H+ ions
acts as a channel protein for facilitated diffusion of H+ ions
describe how quaternary structure of protein is formed
amino acids join by peptide bonds
condensation reaction
secondary structure is formed by hydrogen bonds
tertiary structure is formed by R-group interactions
quaternary structure is due to presence of more than 1 polypeptide chain
describe other processes that result in increases in genetic variation
crossing over - homologous chromosomes pair to form bivalents, sections of chromatids break and exchange to form genetically diverse chromosomes
independent segregation- homologous chromosomes line up at the equator and separate randomly
random fertilisation
all produce new combinations of alleles
describe breathing in
diaphragm contracts and flattens
external intercostal muscles contract and ribcage is pulled up and out
thoracic cavity volume increases and pressures decreases
describe the induced fit model of enzyme action and how an enzyme acts as a catalyst
- substrate binds to the active site/ ES complex forms
- active site changes slightly so it is complementary to substrate
- reduces activation energy
suggest and explain a procedure to stop an enzyme catalysed reaction
- boil sample/ add conc acid or alkali
- denatures enzyme preventing enzyme-substrate complexes from forming
explain the advantages for larger animals of having specialised system that facilitates oxygen uptake
- larger organisms have a smaller surface area : volume ratio
- this overcomes long diffusion pathway
why do fish have an oxygen uptake system outside the body and humans have it inside
4
- water has a lower oxygen partial pressure/conc than air
- fish system outside gives larger surface area in contact with water
- water is more dense than air
- so water supports gills
explain how the counter-current principle allows efficient oxygen uptake in the fish gas exchange system
- blood and water flow in opposite direction
- allows for a steep concentration gradient to be established throughout the whole length of the lamella
describe how one amino acid is added to a polypeptide that is being formed at a ribosome during translation
- tRNA brings specific amino acids to ribosomes
- anticodon on tRNA binds to mRNA codon
- amino acids join by condensation reaction/ forming a peptide bond
3 ways to improve quality of scientific drawing
- do not use sketching or hatching
- add magnification/ scale bar
- draw all parts to scale
- clear labels
describe how a sample of chloroplasts could be isolated from leaves
break open cells/ homogenise and filter/grind and blends leaves and filter
place in cold, isotonic, pH controlled solution
centrifuge and remove nuclei/cell debris
centrifuge/spin at higher speed, chloroplasts settle out
difference between chloroplast DNA and nuclear DNA
chloroplast DNA not associated with histones
difference between chloroplast ribosomes rest of the cell ribosome
smaller than cytoplasmic ribosomes
why do iron-deficient plants have reduced growth
- less thylakoid membrane/fewer grana
- smaller surface area / less chlorophyll
- less light absorption
- slower rate of photosynthesis
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3.1 Biological Molecules212
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2.1 Cell structure and Division109
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2.2 All cells arise from other cells26
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2.3 Cell membranes30
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2.4 Cell Recognition and The Immune System47
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3.1 Surface area to volume ratio12
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3.2 Gas Exchange44
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3.3 Digestion and Absorption25
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3.4 Mass Transport13
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3.4.1 Mass transport in Animals81
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3.4.2 Mass transport in plants7
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4.1 DNA Genes And Chromosomes15
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4.2 DNAS, RNA and Protein synthesis46
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4.3 Genetic diversity can arise as a result of mutation or during meiosis21
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4.4 Gentetic Diversity And Adaptation19
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4.5 Species and Taxonomy12
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4.6 + 4.7 Biodiversity within a community23
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5.1 Photosynthesis37
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5.2 Respiration36
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5.3 Energy and ecosystems26
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5.4 Nutrient Cycles3
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3.6.1.Stimuli, both internal and external are detected and lead to a response53
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6.2 Nervous Coordination82
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6.3 Skeletal muscles are stimulated to contract by nerves and act as effectors21
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6.4 Homeostasis34
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7.1 Inheritance23
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7.2 Populations7
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7.3 Evolutions may lead to a speciation13
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7.4 Populations in an ecosystem23
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8.1 Alteration of the sequence of bases in DNA can alter the structure of proteins12
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8.2 Gene expression is controlled by a number of features44
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8.3 Using genome projects7
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8.4 - Gene technologies28
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wrong answers41
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6 markers62
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stats and calculations4
