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A Biology A Level > Topic 2 > Flashcards

Topic 2 Flashcards

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1
Q

What are the properties of gas exchange surfaces?

A
  • Large surface area to volume ratio of alveoli
  • Lots of capillaries and thin walls in diffusion pathway
  • Concentration gradient
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2
Q

How does surface area to volume ratio affect different organisms gas exchange?

A
  • As an organism gets larger the sa:v ration decreases.
  • Smaller sa:v means more need for exchange surface/system
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3
Q

What is Fick’s law?

A

rate of diffusion ∝ (surface area x difference in concentration) / thickness of exchange surface

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4
Q

How does Fick’s law explain adaptation of mammalian gas exchange surfaces?

A
  • Rate of diffusion is proportional to surface area
  • Diffusion distance shortened due to flattened cells forming alveoli and capillary walls
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5
Q

What are the adaptations of the lungs?

A
  • Large surface area
  • Large capillary network for blood supply
  • Short diffusion distance
  • Alveoli + cilia hair
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6
Q

How are alveoli adapted for gas exchange?

A
  • Large blood supply to create steep concentration gradient
  • Wall is one cell thick
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7
Q

What is the structure of a cell membrane?

A
  • Phospholipid bilayer with hydrophilic phosphate head + hydrophobic fatty acid tail
  • Contains proteins, cholesterol, glycoproteins and glycolipids
  • Lipid bilayer closes so no exposed hydrocarbon chain to form stable layer.
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8
Q

What is the ‘Fluid Mosaic model’?

A
  • Molecules are dynamic and move in the plane of the membrane instead of static for cell movement and interactions and signalling
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9
Q

What is the function of integral proteins?

A
  • Embedded into the membrane and transport substances across membrane
  • Channel proteins allow water-soluble molecules to cross
  • Carrier proteins bind and change shape of proteins
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10
Q

What is the function of peripheral proteins?

A
  • Attaches to the outer surface
  • Act as receptors to bind to + recognise
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11
Q

What are glycoproteins?

A
  • Proteins with a carbohydrate attached
  • Act as a recognition site, help form tissue, provide stability and act as receptors
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12
Q

What are glycolipids?

A
  • Proteins with a lipid attached
  • Act as a recognition site, help form tissue, provide stability and act as receptors
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13
Q

What is the role of cholesterol?

A
  • Lipid molecule
  • Found between phospholipids where is maintains membrane fluidity
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14
Q

What is diffusion?

A
  • Overall net movement of molecules or ions from high to low conc, down conc gradient
  • Passive transport as without ATP
  • Continues until equilibrium
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15
Q

What is facilitated diffusion?

A
  • Across a partially permeable membrane via transmembrane integral proteins
  • For large, polar molecules
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16
Q

What do Channel proteins do vs Carrier proteins?

A
  • Channel are selective to particles and open and close from one side of the membrane to the other
  • Carrier have specific molecules bind and change in shape to transport across membrane.
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17
Q

What is osmosis?

A
  • Net movement of water molecules across a partially permeable membrane, down water potential gradient.
  • Low conc of solution to high conc of solute
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18
Q

What is active transport?

A
  • Movement from low conc to high conc against a concentration gradient
  • Requires ATP and carrier proteins.
  • ATP hydrolysed to ADP and Pi which causes carrier protein to change shape.
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19
Q

What is endocytosis?

A
  • Takes substances in
  • Membrane fuses enclosing substance in a vesicle
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20
Q

What is exocytosis?

A
  • Release of substances
  • Secretory vesicle moves to cell surface membrane to release material
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21
Q

What are enzymes?

A
  • Biological catalysts which speed up the rate of reaction
  • Catalyses reaction by lowering activation energy
  • Activation energy is energy requires to start a reaction
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22
Q

What are substrates?

A
  • Any molecules catalysed by an enzyme
  • Only binds with specific active sites - complementary binding
  • Form enzyme-substrate complexes with enzymes
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23
Q

What is the induced fit model?

A
  • Specific shape substrate will induce an active site
  • Binding causes active site to change its shape allowing reaction to be catalysed.
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24
Q

How do enzyme and substrate conc affect rate of reaction?

A
  • More enzymes produce more enzyme substrate collisions so increase rate.
  • More substrate means more collisions but when all active sites are full it does not effect rate.
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25
Q

What is DNA?

A
  • Deoxyribonucleic acid
  • Contains all genetic material + hereditary material
  • It is a polynucleotide (polymer chain of nucleotides)
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26
Q

What is a nucleotide made up of?

A
  • Pentose sugar
  • Phosphate group
  • Organic base
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27
Q

What are the organic bases in DNA?

A
  • Guanine, adenine, cytosine, thymine
  • A + T, C + G
  • Either purine (two carbon rings) or pyrimidine (one carbon ring)
  • Purine pairs with pyrimidine
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28
Q

How are mononucleotides formed?

A
  • Joined in condensation reaction
  • By hydroxyl group of phosphate group + pentose sugar
  • Forms phosphodiester bond
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29
Q

What is the structure of DNA?

A
  • Two polynucleotides twist to form a double helix
  • Sugar and group form sugar-phosphate backbone
  • Strands are held by hydrogen bonds
  • Run antiparallel
  • One runs 5’ to 3’, one runs 3’ to 5’
30
Q

What is RNA?

A
  • Acts as a messenger molecule to transfer and regulate cell
  • It is single stranded
  • Pentose sugar is ribose
  • Uracil instead of thymine
31
Q

What are genes?

A
  • Sections of DNA used to code for a specific amino acids in a polypeptide
32
Q

What is a protein?

A
  • Made of multiple polypeptides
  • The primary structure determines the 3d shape the protein folds
  • Structural, metabolic + transport roles
  • Made up of carbon, hydrogen + oxygen
33
Q

What is the genetic code?

A
  • Specific sequence of bases that code for a specific sequence of amino acids in protein synthesis
34
Q

What is the features of the genetic code?

A
  • Triplet code
  • Degenerate code
  • Universal
  • Non overlapping
35
Q

How is the code degenerate?

A
  • An amino acid can be coded for more than one code.
  • 20 amino acids, but 64 combinations of codons
  • Valine can be coded for by GUU, GUC, GUA, GUG
36
Q

What is a codon?

A
  • 3 bases that code for an amino acid
  • There is start and stop codon
37
Q

What are start and stop codons?

A
  • Start codon always AUG, codes for amino acid Methionine.
  • Stop codon are UGA, UAA, UAG. tRNA molecules which do not have corresponding amino acid so no peptide bond can be formed.
38
Q

What is mRNA?

A
  • From DNA and transfers genetic information from nucleus to cytoplasm
39
Q

What is transcription?

A
  • DNA double helix is unzipped and hydrogen bonds break by the enzyme DNA helicase which moves along sugar-phosphate backbone
  • Template antisense strand acts as a template for free RNA nucleotides to pair with complementary bases
  • RNA nucleotides are joined to adjacent nucleotides by phosphodiester bonds by the enzyme RNA polymerase.
  • Makes mRNA which leaves nucleus via nuclear pore
40
Q

What is tRNA?

A
  • Transports amino acid to ribosome
  • Binds to one amino acid and the specific mRNA codon creating a link
41
Q

What is translation?

A
  • mRNA enters cytoplasm, moves to ribosomes
  • tRNA molecules with their specific amino acid, move into ribosome and bind to mRNA (anticodon binds to start codon) by hydrogen bonding
  • Second tRNA with complementary anticodon binds to next codon, bringing its specific amino acid
  • allowing peptide bond to form between the amino acids
  • tRNA detaches from mRNA and leaves into cytoplasm.
  • Amino acids form the polypeptide primary structure.
42
Q

What is the structure of amino acids?

A
  • Amine group
  • Carboxyl group
  • R groups (differ in size, polarity, charge)
43
Q

How are two amino acids joined?

A
  • In condensation reaction between carboxyl and amine group
  • A peptide bond is the covalent bons formed when two amino acids are joined
  • Hydrolysis reaction breaks down amino acids
44
Q

How is a protein formed?

A
  • A protein is formed when one or more polypeptide chain folds into a specific shape
45
Q

What is a polypeptide?

A
  • A polymer of many amino acids joined by peptide bonds
46
Q

What is the primary structure of a protein?

A
  • Sequence of amnio acids joined with peptide bonds
  • Determines folding of polypeptide
47
Q

What is the secondary structure of a protein?

A
  • Chains folding and shapes arise due to structure of amino acids
  • Alpha-helix is when polypeptide coils and twists with hydrogen bonds
48
Q

What is the tertiary structure of a protein?

A
  • 3d structure of amino acids
  • Hydrogen bonds form between polar R groups
  • Ionic bonds form between positive and negative R groups
  • Disulphide link form between sulphur atoms in R groups
  • Hydrophobic R group found in centre of protein and hydrophilic found on outside
49
Q

What is the quaternary structure of a protein?

A
  • Proteins determined by more than one polypeptide chain
50
Q

What is a Globular protein?

A
  • A spherical polypeptide with hydrophobic R group inside and hydrophilic R group outside
  • Insoluble in water
  • Eg. enzymes, hormones
51
Q

What are Fibrous proteins?

A
  • Long chains of polypeptides with non polar R groups
  • Soluble in water
  • Eg. cartilage, collagen
52
Q

What is DNA replication?

A
  • DNA double helix unzipped to break hydrogen bonds by DNA helicase
  • Forms a replication fork with two exposed strands which acts as a template.
  • Free DNA nucleotides pair with complementary based and DNA polymerase link adjacent nucleotides
  • Phosphodiester bonds form in condensation reaction
53
Q

What is semi conservative replication?

A
  • There is one original strand and one new strand
54
Q

What was the Meselson and Stahl experiment?

A
  • E-coli is grown in heavy N15 isotopes
  • Bacteria then moved to N14 meaning new nucleotides were light but original were heavy
  • Spun in a centrifuge and produced medium DNA.
  • New strand contained both light and heavy nitrogen
55
Q

What are mutations (gene + chromosome)?

A
  • Changes to the genetic material of a cell
  • Gene mutations are changes to vase sequence within a section of DNA or gene
  • Chromosome mutations are changes to structure of whole chromosomes
  • Important to evolution as increases genetic variation
56
Q

What are substitution mutations?

A
  • Nucleotide is replaced with another nucleotide that has a different base
  • Changes base sequence so changes the codon
57
Q

What are deletion mutations?

A
  • Nucleotide removed from DNA sequence
  • Shifts the reading chain so changes all amino acids
58
Q

What are insertion mutations?

A
  • Additional nucleotide in DNA sequence
  • Changed reading frame
59
Q

What are the type of affects of mutations?

A
  • Silent - no change to protein function (explained by degenerate codon)
  • Missense - change of amino acid form, so changes tertiary structure to non functioning protein
  • Nonsense - previously coded amino acids becomes a stop codon (stops translation so polypeptide would end)
60
Q

What is sickle cell anaemia?

A
  • Affects haemoglobin
  • Substitution mutation changing encoded amino acid
  • Forms insoluble fibres forming red blood cells to be distorted so less oxygen and inefficient transport
61
Q

What is cystic fibrosis?

A
  • A mutation in the CFTR gene which leads to production of non functional chloride ion channel proteins
  • Reduces the movement of water via osmosis into the mucus
62
Q

What impacts does cystic fibrosis have on the respiratory system?

A
  • Cilia unable to move thick and sticky mucus so microorganisms are not removed from the lungs and lung infections occur more frequently
  • Mucus builds up in the lungs and can block airways
  • SA for gas exchange reduced
63
Q

What is genetic testing?

A
  • Identifies abnormal alleles of genes in DNA.
  • Confirms diagnosis, identifies carriers, test embryos
64
Q

How are embryos tested?

A
  • Amniocentesis - prenatal testing where a needle collects amniotic fluid and are screened
  • Chorionic villus - prenatal testing where small sample of placental tissue removed and screened
  • Non - invasive prenatal diagnosis - DNA fragments of blood plasma.
  • Pre implantation diagnosis - IVF for creation of embryos where they are removed and screened at 8-stage cell
65
Q

What is the difference between a genotype and a phenotype?

A
  • Genotype is all the genetics of an organism
  • Phenotype is the observable characteristics of an organism which are influence by both genotype and environment
66
Q

What is an allele?

A
  • Genes of two or more different forms
  • Gene is hereditary information where as allele is a form of a gene
67
Q

How are chromosomes formed?

A
  • DNA is packaged with histone proteins that are called chromatin
  • That coils and condenses to form chromosomes
68
Q

What are homologous chromosomes?

A
  • A pair of chromosomes
  • The position of a gene on a chromosome is called a locus
69
Q

What is homozygous vs heterozygous?

A
  • If a pair of chromosomes have the same alleles at a locus
  • If a pair of chromosomes have different alleles at a locus then it is heterozygous
70
Q

What are two dominant alleles called?

A
  • Homozygous dominant
71
Q

What are two recessive alleles called?

A
  • Heterozygous recessive

A Biology A Level (8 decks)

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