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A Level Biology (SNAB) > Topic 2 > Flashcards

Topic 2 Flashcards

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1
Q

What happens when you inhale?

A
  • Intercostal muscles contract to lift the ribs up and outwards
  • The diaphragm muscles contract to flatten the diaphragm
  • This creates a larger volume inside the lungs so that pressure decreases
  • Air is drawn into the lungs along the pressure gradient
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2
Q

What happens when you exhale?

A
  • Intercostal muscles relax so the ribcage drops down and inwards
  • The diaphragm muscles relax and move upwards
  • This creates a smaller volume in the lungs and so pressure increases
  • The increased pressure forces the air out of the lungs
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3
Q

What is the rate of gas exchange affected by?

A
  • The surface area available for diffusion
  • Length of diffusion pathway
  • Conc. gradient across gas exchange surfaces
  • The speed of molecules diffusing through membrane, which is affected by;
  • Mass of the molecule
  • Permeability of membrane
  • Temperature and pressure of the molecule
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4
Q

What must efficient gas exchange systems have?

A
  • Have a large SA:V ratio (circular alveoli)
  • Be thin (lung walls)
  • Be able to keep a steep conc. gradient (blood and capillaries)
  • Be permeable to gases
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5
Q

What is the structure and function of Alveoli?

A
  • Moist surface = oxygen dissolves and diffuses through wall into capillary
  • Thin walls = small diffusion pathway, squamous epithelium
  • Capillary walls = small interstices where O2 pass into blood
  • Spherical = large SA:V
  • Pulmonary Surfactant = lowers tension of mucus to allow gases to diffuse in and out
  • Capillaries cover each alveoli = O2 and CO2 can diffuse in/out of blood plasma
  • Squamous = covered w/ characterised by scales
  • Squamous epithelial cells are thin and disc shaped like scales
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6
Q

What is the equation for Fick’s Law?

A

Rate of diffusion ά SA x Dif in Conc.
————————————————-
thickness of gas exchange surface

ά = directly proportional to

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7
Q

What is the structure of Amino Acids?

A
  • Check diagram
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8
Q

What are condensation reactions?

A
  • Condensation reactions form peptide bonds, hydrolysis breaks them
  • A condensation reaction joins two amino acids together to form a dipeptide and H2O
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9
Q

What is the primary protein structure?

A
  • Primary structure = linear amino acid sequence of the polypeptide chain
  • Determined by the DNA sequence of the gene coding for a protein
  • Peptide bonds (PP)
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10
Q

What is the secondary protein structure?

A
  • Secondary Structure = folding of the protein chain, eg. into an alpha helix
  • Hydrogen bonds (SH)
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11
Q

What is the tertiary protein structure?

A
  • Tertiary Structure = further folding and attractions b/w alpha helices or beta pleated sheets to give a specific 3D shape, eg. enzymes (one polypeptide chain)
  • Di-sulfide bridges (TD)
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12
Q

What is the quaternary protein structure?

A
  • Quaternary Structure = a protein that consists of more than one polypeptide chain
  • Eg. Haemoglobin consists of 4 polypeptide chains
  • Ionic, covalent or hydrogen bonds (QHIC)
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13
Q

What is the original Primary structure = 3D structure in Tertiary structure

A
  • The order and number of amino acids (and their R group) means hydrogen bonds will form in different places
  • Hydrogen bonds forming in different place means different secondary structures
  • More bonding dependent on its amino acids = tertiary structure
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14
Q

What are globular proteins?

A
  • Globular proteins = ball-like proteins where hydrophobic parts are towards the centre, and the hydrophilic parts are towards the edges
  • Are water soluble b/c of placement of hydrophobic/philic parts
  • Eg. enzyme and antibodies
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15
Q

What are fibrous proteins?

A
  • Fibrous proteins = proteins formed from long fibres, and consist mostly of repeated amino acid sequences
  • Insoluble in water and used in structural roles
  • Eg. collagen in bones and keratin in nails and hair
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16
Q

What are integral proteins?

A
  • Channel proteins = allow the transport of specific substances across a membrane
  • Facilitated diffusion and passive transport
  • Polar molecules, such as, water and sugars
  • Carrier Proteins = make diffusion across a membrane easier
  • Active transport
  • Charged particles, such as, ions
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17
Q

What are phospholipids?

A
  • Structure = two fatty acid tails joined together by a glycerol molecule
  • Properties = head is polar/ hydrophilic, two fatty acid tails are non polar/ hydrophobic
  • Are arranged into a bilayer
  • Hydrophilic head arranges itself so it’s directly exposed to water molecules
  • Hydrophobic tail isolates itself from water, does by having the hydrophilic heads on either side of them
  • Non polar molecules that can diffuse through:
    O2 and CO2
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18
Q

What is the fluid mosaic model?

A

Fluid = molecules are free to move about
Mosaic = proteins are randomly distributed
Differences inc.
Proteins are intrinsic
Some proteins are extrinsic, and are attached to a sugar or lipid chain
Cholesterol is present
Molecules are free to move

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19
Q

What is the structure of the fluid mosaic model?

A
  • Glycoprotein = proteins w/ a sugar attached covalently to polypeptide chain
  • Glyco-lipid = lipids w/ a carbohydrate attached by a glycosidic bond
  • Maintain stability of the membrane
  • Facilitate cellular recognition
  • Peripheral proteins = adhere temporarily to the biological membrane, w/ hydrogen bonds
  • Extrinsic proteins = loosely attached by ionic bonds or calcium bridges to the electrically charged phosphoryl surface of the membrane
  • Serve in transport of molecules as receptors
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20
Q

What is osmosis?

A
  • Osmosis = the facilitated diffusion of water from an area of high free water conc. to an area of low free water conc. via channel proteins
  • High free water = high water potential, eg. pure water = 0ψ
  • Low free water = low water potential, eg. concentrated solution = -120ψ
  • The more -ve the water potential the more concentrated the solution
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21
Q

What is Active Transport?

A
  • Against a conc. gradient (low -> high)
  • Requires ATP energy to make carrier proteins change shape (aerobic respiration)
  • Carrier proteins needed
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22
Q

What is facilitated diffusion?

A
  • With a conc. gradient (high -> low)
  • Passive transport (doesn’t require energy)
  • Uses channel proteins
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23
Q

What is simple diffusion?

A
  • Same as facilitated, except no proteins
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24
Q

What is Endocytosis?

A
  • Bulk transport into a cell (large volume of molecules)
  • ATP energy used in the movement of vesicles in through the plasma membrane
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25
Q

What is exocytosis?

A
  • Bulk transport out of a cell
  • ATP energy used in the movement of the vesicle out through the plasma membrane
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26
Q

What is the function of the lungs without CF?

A
  • When mucus is wet
  • Na+ pump produces a high conc. of Na+ ions outside the cell at the basal end
  • By actively transporting Na+ ions out of the cell (Channel proteins)
  • Na+ ions diffuse in to replace those pumped out, which lowers the ψ of mucus (facilitated diffusion via channel proteins)
  • Water is lost b/c osmosis, which draws water out of the mucus at the apical end in response
  • When mucus is dehydrated
  • The CFTR channel opens, so Cl- ions diffuse out (facilitated diffusion)
  • The CFTR channel stops the Na+ channel from allowing Na+ ions to enter
  • Cl- and Na+ ions build up in the mucus and reverse the direction of osmosis
  • More water enters mucus reducing viscosity
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27
Q

What are the effects of CF on the respiratory system?

A
  • Cilia are unable to move the mucus b/c its too thick
  • Mucus builds up in airways
  • Airways become blocked
  • Lung infections may occur b/c the mucus contains bacteria
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28
Q

What is CF?

A
  • The CFTR protein is absent or doesn’t function properly
  • w/o it there is no Cl- ions leaving the cell and no regulation of the Na+ channel
  • Ψ inside cell cytoplasm remains more -ve than ψ in the mucus
  • The direction of osmosis can’t be reversed in response to dehydrated mucus
29
Q

What are the effects of CF on the reproductive system?

A
  • Pancreatic duct becomes blocked w/ mucus
  • Digestive enzymes can’t reach small intestine
  • Mucus lining the small intestine is thick
  • Malnutrition may occur b/c can’t absorb nutrients in food
30
Q

What are the effects of CF on the digestive system?

A
  • In men, sperm are prevented from reaching the penis
  • In women, cervical mucus is thick preventing sperm reaching the egg
31
Q

What is the enzyme structure?

A
  • Proteins in enzymes are globular, and in their secondary and tertiary structure
  • Many consist of a protein and a non-protein (called the cofactor)
  • Have intra and intermolecular bonds, which are affected by pH and temperature
32
Q

How do enzymes function? (Lock and Key)

A
  • Lock-and-key hypothesis
  • States that shape of active site and substrate are the same
  • When a substrate collides w/ same shape active site it will fit together and form enzyme-substrate complex
  • Enzyme will catalyse the reaction
  • The products and enzyme will form an enzyme-product complex
  • Model suggests that enzymes can catalyse reverse reactions
33
Q

How do enzymes function? (Induced Fit)

A
  • States active sites are not exactly complimentary
  • Change shape when near a specific substrate to fit it
  • When a substrate collides w/ an enzyme, if its composition is specifically correct the shape of the active site will change
  • Substrate then fits and forms enzyme-substrate complex
  • Reaction is then catalysed and enzyme-product complex forms
34
Q

What are inhibitors?

A

Molecules that interfere w/ substrate binding to active site (slowing down or stopping)
Can be reversible (competitive and non-competitive) or non-reversible

35
Q

What is Activation Energy?

A
  • When substrates react they need to form a complex called the transition state
  • This state has higher energy levels than substrates and products
  • The high temperatures are hazardous in the body (and kills cells)
  • Enzymes provide a different transition state and lower activation energy
  • ↓by putting stress on bonds within molecule or by holding molecules closer together
  • ↑likelihood of a reaction so lowers the energy required to begin the reaction
36
Q

How does pH affect the rate of an enzyme controlled reaction?

A
  • Enzymes have an optimum pH (8)
  • pH changes so chemical nature of amino acids can change, by adding/ removing a proton and changing the amino acids charge
  • Change can result in a change in hydrogen bonds
  • Meaning active site is disrupted and enzyme is denatured
37
Q

How does temperature affect the rate of an enzyme controlled reaction?

A
  • Work best at an optimum temperature (37.5)
  • ↑means↑rate of activity as more kinetic energy to the molecules
  • Meaning no. of collisions b/w enzyme and substrate will ↑so rate will too
  • A much ↑ temperature causes amino acids to vibrate
  • This breaks the weak hydrogen bonds and change the structure of the enzyme meaning its denatured
38
Q

How does substrate conc. affect the rate of an enzyme controlled reaction?

A
  • ↑substrate conc. will↑rate until enzyme is working as fast as possible
  • ‘Fast as’ is when all active sites are filled all the time
  • Only way to ↑rate further is ↑enzyme conc.
39
Q

How does enzyme conc. affect the rate of an enzyme controlled reaction?

A
  • Low conc. = great competition for active sites = low rate of reaction
  • ↑conc. means more active sites =↑rate of reaction
  • ↑ conc. too high has no effect as substrate conc. becomes the limiting factor
40
Q

What is DNA?

A
  • DNA is a polymer of nucleotides
  • A nucleotide contains a Nitrogenous base, phosphate group and a deoxyribose sugar
  • 4 bases: Adenine, Thymine, Guanine and Cytosine
  • Form specific base pairings due to weak hydrogen bonds that form b/w them
  • In a gene 3 bases in a row is called a triplet code, which codes for one amino acid
  • The nucleus also contains free nucleotides
  • Phosphodiester bonds form b/w nucleotides in DNA through a condensation reaction
  • Which are stronger than hydrogen bonds
41
Q

What is the structure of DNA?

A
  • Phosphate group - obtained by eating other cells in our diet, eg. Phospholipid membranes
  • Nitrogenous base - converted from amino acids from eating plant and animal proteins in our diet
  • C=G triple hydrogen bond
  • A=T double hydrogen bond
  • In RNA A=U double hydrogen bond
42
Q

What is DNA replication and how does it work?

A
  • Each strand is complementary of each other
    1. DNA uncoils (in a very organised way a bit at a time) and unzips (breaking hydrogen bonds)
    Enzyme = DNA helicase
    2. Free DNA nucleotides will join with the existing DNA molecule
    Enzyme = DNA polymerase
    3. Forms phosphodiester bonds b/w adjacent nucleotides
    Enzyme = DNA ligase
43
Q

What is a gene?

A
  • A gene = a sequence of bases on a DNA molecule coding for a sequence of amino acids in a polypeptide chain
  • The location where a gene is found on a chromosome = locus
44
Q

How does transcription work?

A
  • Nucleus is Transcription
    1. DNA Helicase unwinds and unzips a section of the DNA
    2. Free RNA nucleotides complementary base pair with the DNA template strand, and RNA polymerase catalyses the reaction of hydrogen bonds forming b/w bases
    3. RNA ligase forms phosphodiester bonds between the RNA nucleotides to produce a molecule of mRNA
45
Q

How does translation work?

A
  • Cytoplasm is Translation
    1. The mRNA molecule diffuses out of the nucleus via a nuclear pore
    2. The mRNA attaches to a ribosome, which then reads the mRNA a codon at a time
    3. This triggers tRNA to bring over an amino acid that has a complementary codon
    4. The tRNA molecule ‘drops off’ the amino acid, which then binds to the complementary bases, and the chain forms a protein
46
Q

Meselson and Stahl Experiment

A
  • Meselson and Stahl’s experiment - 15N 14N
  • Grew bacteria in a growth medium containing ammonium ions as the source of N
  • The type of DNA made depends on the type of Nitrogen present
  • 14N is the light form of Nitrogen, while 15N is the heavier form
  • Bacteria containing DNA made from 15N was allowed to divide in a solution of 14N
  • The DNA was then extracted and centrifuged, and had a medium density
  • This supports the semi-conservative theory b/c “the two new strands both contain one of the original parent strands”
47
Q

Compare and contrast DNA and RNA

A
  • Both have a phosphate group, pentose sugar and nitrogenous bases in the nucleotides
  • DNA contains deoxyribose sugar while RNA contains ribose
  • DNA is double stranded, while RNA is single stranded
  • DNA contains thymine, whereas, RNA contains uracil
48
Q

Compare and contrast mRNA and tRNA

A
  • Both contain RNA nucleotides
  • Both are single stranded
  • mRNA doesn’t have H bonds b/w bases, but tRNA does
  • mRNA is linear, whereas, tRNA is non-linear
  • mRNA has a codon while tRNA has an anticodon
49
Q

What is protein synthesis and how does it work?

A
  • Antisense strand = template strand
  • The mRNA is complementary to this
  • Sense strand = what the mRNA is actually making
  • If DNA is replicated from the 5’ to 3’
  • Then transcription enzymes move from 3’ to 5’
  • mRNA needs to be read in the correct direction by a ribosome
50
Q

What is a mutation?

A
  • Mutation = a change to a DNA base sequence
  • A codon codes for a specific amino acid
  • If a mutation occurs the wrong amino acid could be put into the polypeptide chain
  • In dong so different bonds would form b/w the different R groups
  • Leading to ineffective/ lack of enzyme as there would be a different tertiary structure
  • Though not always as different codons can code for the same amino acid
51
Q

What is the definition of a gene?

A
  • Gene = a sequence of bases on a DNA molecule coding for a sequence of amino acids in a polypeptide chain // a segment of a DNA molecule made up of alleles
52
Q

What is the definition of alleles?

A
  • Alleles = the different forms that comprise a gene
53
Q

What is the definition of genotypes?

A
  • Genotype = the alleles that cause the expression of the phenotype
54
Q

What is the definition of phenotypes?

A
  • Phenotype = how the gene is expressed in a person
55
Q

What is the definition of Reccesive?

A
  • Recessive = need to have a homozygous genotype to be expressed
56
Q

What is the definition of Dominant?

A
  • Dominant = can be a homozygous or heterozygous for the allele to be expressed
57
Q

What is the definition of Incomplete dominance?

A
  • Incomplete Dominance = a heterozygous condition where both alleles at a locus are partially expressed (which produces an intermediate phenotype)
58
Q

What is the definition of Codominance?

A

Codominance = both alleles will be expressed as both are dominant

59
Q

What is the definition of Sex-linked?

A
  • Sex-linked = a disease passed through the X chromosome
60
Q

What is the definition of a Homozygote?

A
  • Homozygote = an individual who has two copies of the same allele at a locus
61
Q

What is the definition of a Heterozygote?

A
  • Heterozygote = an individual who has two different alleles at a genetic locus
62
Q

What is prenatal screening (Amniocentesis)?

A
  • Amniocentesis = inserting a needle through the abdomen and removing some fluid from the amniotic sac (22 weeks gestation)
63
Q

What are the advantages of prenatal screening (Amniocentesis)?

A
  • Confirms if abnormality is present in a fetus
  • Offers a specific diagnosis chromosomal or genetic abnormality before birth
  • Allows early preparation for child w/ birth defect or allows decision on abortion
  • Is more accurate as baby is more developed
64
Q

What are the disadvantages of prenatal screening (Amniocentesis)?

A
  • Miscarriage can occur (0.5-1%)
  • Mother may experience side effects
  • Limited time to make the decision on carrying to full term or not
  • Longer wait for results (1-2 weeks=↑stress)
65
Q

What is Chorionic Villus Sampling?

A
  • Chorionic Villus Sampling = inserting a needle through the vagina and removing a few cells from the early placenta (chorion) (12 weeks gestation)
66
Q

What are the advantages of Chorionic Villus Sampling?

A
  • Can be performed earlier than amniocentesis, meaning more time to prepare/ make a decision
  • Carries less risk from an abortion if that is the decision made
  • Is better at diagnosing certain conditions
  • Tissue obtained is preferable for DNA analysis
67
Q

What are the disadvantages of Chorionic Villus Sampling?

A
  • More difficult technically than amniocentesis
  • Complications, such as, miscarriage and limb deformities may occur
  • Higher risk of miscarriage (2-3%)
  • Is less accurate as foetus isn’t fully developed
68
Q

What are the other types of screening?

A
  • Preimplantation screening = screening embryos fertilised by IVF before implanted into a uterus
  • Pre Symbiotic screening = screening to predict adult onset diseases
  • Pre-symptomatic screening = screening to estimate the risk of developing cancer or - Alzheimer’s as an adult
  • Forensic/ Identity testing = screening to eg. determine the father
69
Q

What are the Ethical/ Social/ Moral Issues with Genetic screening?

A
  • Employers and insurers may want know and use the information gained
  • The chance it is incorrect may lead to abortion of a healthy child
  • Or the birth of a child with a serious disease
  • May lead to medical enhancement/ design a baby
  • What about people who may not be eligible/ afford the tests
  • Should testing of a disease be performed on a baby if there is no cure
  • The general issues with abortion // gods plan etc.
  • People may not be mentally ready to know the diseases they may develop
  • Will cause long term stress, especially if it’s an adult onset disease

A Level Biology (SNAB) (4 decks)

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