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A Level Biology (SNAB) > Topic 2 > Flashcards

Topic 2 Flashcards

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1
Q

Diffusion

A 
Net movement of particles
Down a the concentration gradient (high ->low)
Across a partially permeable membrane
Particles diffuse both ways
Passive process
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2
Q

Gas Exchange Surfaces

A

Large surface area to volume ration
Thin -> short diffusion pathway
Steep concentration gradient maintained

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3
Q

Features of Lungs

A
  1. Lots of alveoli -> large SA
  2. Alveolar epithelium and capillary endothelium = 1 cell thick -> short diffusion pathway
  3. Good blood supply (maintain conc. gradient)
  4. Breathing -> refreshes air + mantain conc. gradient
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4
Q

Lungs gas exchange surface

A

Alveolar epithelium

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5
Q

Alveoli process

A
  1. oxygen diffuse out of alveoli
  2. Crosses the alveolar epithelium (thin, flat cell layer) + capillary endothelium -> blood
  3. Carbon dioxide diffuses into the alveoli -> breathed out
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6
Q

Lung structure

A

ngng

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7
Q

Alveoli structure

A

ngng

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8
Q

Fick’s Law

A

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

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9
Q

P x A x ((C1 - C2) /T)

A 
= Rate ; Fick's Law
P = permeability constant
A = surface area
(C1 - C2) = difference in concentration
T = thickness in exchange surface
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10
Q

Cell membranes

A

‘Fluid Mosaic’ Structure (suggested in 1972)
Phospholid bilayer -> fluid = lipids constantly moving
Partially permeable:
- gaps inbetween phospholipids -> small molecules pass through
- membrane proteins (Channel + Carrier) -> large molecules + ions

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11
Q

Phospholipid bilayer

A

Phospholipid:
- Head = phosphate group -> hydrophillic
- Tail = two fatty acids -> hydrophobic
Bilayer:
- Two phospholipids
- Automatic bilayer of heads facing water outside/inside membrane
- Centre = hydrophonic -> water solubles cannot enter

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12
Q

Fluid Mosaic Model

A
  1. Fluid = Phospholipid bilayer (fluid lipids can switch adjacently and opposite but rare, tend to move linearly)
  2. Mosaic = protein molecules scattered throughout ( can move around)
  3. Glycoprotein = protein + polysaccharide chain
  4. Glycolipid = lipid + polysaccharide chain
  5. Cholestrol between phospholipids -> forms bonds -> membrane = more rigid
  6. Channel + Carrier Proteins
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13
Q

Osmosis

A

H2O diffuses across partially permeable membrane
Down concentration gradient
Diffuses both ways -> net movement to lower side

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14
Q

Active Transport

A

Moves molecules + ions against the concentration gradient
Across a plasma membrane
Requires energy from ATP

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15
Q

Active Transport mechanism

A
  1. Molecule attaches to carrier protein -> changes shape
  2. Molecule moved across plasma membrane -> released
  3. Energy used = ATP:
    - produced via respiration (immediate energy source)
    - ATP hydrolysed -> energy released
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16
Q

Facilitated Diffusion

A

Passive transport via carrier + channel protein diffusion
Larger molecules:
- amino acids
- glucose
Different carrier proteins facilitate different molecules

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17
Q

Facilitated Diffusion mechanism

A
  1. Large molecule attaches to carrier protein
  2. Protein changes shape
  3. Releases molecule on opposite side of membrane
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18
Q

Channel proteins

A

Different for each +ve/-ve particle

Form pores in membrane for charged particle diffusion

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19
Q

Endocytosis

A

Large molecules:

  • protein
  • lipids
  • (some) carbs
    1. cell surrounds substance with membrane section
    2. membrane pinches off -> vesicle formed in cell (contains ingested substance)
    3. requires ATP
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20
Q

Phagocytes

A

White blood cell

Perform endocytosis for dead cells + microorganism

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21
Q

Exocytosis

A

Secreted substances produced by the cell:

  • digestive enzymes
  • hormones
  • lipids
    1. Vesicles pinch off from golgi apparatus sacs -> cell membrane
    2. Vesicle fuses with membrane -> secretes substance outside the cell
    3. Some substances inserted straight into the membrane
    4. requires ATP
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22
Q

Proteins

A 
Monomers = amino acids
Dipeptide = 2 amino acids
Polypeptide = 2+ amino acids
Protein = 1 or more polypeptides
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23
Q

Amino Acids

A

Same general structure:
-Amino/Amine group (H2N) + Variable group (R) + Carboxyl group (COOH)
Variable group = carbon containing R group
Bank of 20 amino acids (variation of R)
e.g H2N - RCH - COOH
e.g. Alanine = H2N - (CH3)CH - COOH

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24
Q

Polypeptides

A

Formed via condensation reactions:
- H from amine/amino group
- OH from carboxyl group
Peptide bonds = bonds between amino acids

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25
Q

Primary Protein Structure

A

Sequence of amino acids in polypeptide chain

Determines bonds -> folds in 3D structure

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26
Q

Secondary Protein Structure

A

Hydrogen bonds form between amino acids in chain:

  • Coils into Alpha helix
  • or Folds into Beta pleated sheet
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27
Q

Tertiary Protein Structure

A

Coiled/Folded further -> 3D structure

  • hydrogen + ionic bonds form between different polypeptide
  • disulphide bond (if cysteine = amino group, is present)
  • if a single pp chain = final 3D tertiary structure
    note: bonds determine properties + structure
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28
Q

Quaternary Protein Structure

A

Several different polypeptide chains combined via bonds

e.g. haemoglobin, collagen, insulin

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29
Q

The different bonds of the 4 (protein) structural levels

A 
Primary = peptide
Secondary = hydrogen 
Tertiary = ionic
- disulphide (cysteine present)
- hydrophobic interactions (groups clump together_
- hydrophillic (pushed outside
- hydrogen bonds
Quaternary = determined by tertiary
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30
Q

3D structures

A

Globular

Fibrous

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31
Q

Globular protein structure

A
  1. round + compact; many polypeptide chains
  2. chains coiled up:
    - hydrophillic face outwards
    - hydrophobic face inwards
  3. soluable -> easily transported
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32
Q

Haemoglobin structure

A

Globular protein
4 polypeptide chains:
- iron containing haem group bonds to oxygen (deoxyhaemolobin -> oxyhaemolobin)
Soluable -> transported via red blood cells

33
Q

Fibrous protein structure

A
  1. long chains
  2. insoluable
  3. rope shape (chains highly coiled around one another
  4. lots of bonds -> strong protein -> often supportive tissue
    e. g. Collagen = connective tissue
34
Q

Collagen structure

A

3 polypeptide chain
Wound together in alpha helix
Very strong

35
Q

Enzymes

A

Biological catalysts for metabolic reactions:

  • Cellular level (respiration)
  • whole organism (e.g. digestion)
  1. affect structure + function
  2. are Extra or Intra (cellular)
  3. are proteins
  4. have and active site (with specefic shape)
    - substrate fits into AS
  5. highly specefic
    - related to tertiary structure
  6. lower activation energy of a reaction:
    - 2 substrates held close together -> reduces repulsion
    - breakdown -> fitting into AS strains bonds -> break down easier

note: energy released as product forms

36
Q

Lock + Key model

A

ngng

37
Q

‘Induced Fit’ model

A

ngng

38
Q

Enzyme properties

A

Due to 3D (tertiary) structure (determines shape, in turn determined by primary structure)

  1. Very specific - only one complements substrate -> AS -> catalyse one reaction
  2. Different enzyme -> different tertiary structure -> different shapes AS
  3. Tertiary shape altered -> alters AS -> stops E-S complex
    - caused by pH and Temp
  4. Primary structure determined by gene
    - mutation -> different enzyme structure
39
Q

Enzyme concentration > substrate concentration

A

More active sites
More likely substrate + AS collide -> form E-S complex
Increases rate of reaction
Steadily increases as more AS available (graph)
Note: substrate concentration = limiting factor

40
Q

Enzyme concentration < substrate concentration

A

More substrate = more likely collisions
- true up to saturation point = AS full
Substrate concentration decreases over time
- no variable change = decreased reaction
- initial rate = highest

41
Q

DNA

A

Deoxyribonucleic Acid

Stores genetic info
Two polynucleotide strands
Polymer of mononucleotides:
- Pentose sugar (Deoxyribose)
- Phosphate group
- Nitrogen containing organic base
42
Q

DNA nitrogen containing base variables

A
  1. Guanine
  2. Cytosine
  3. Adenine
  4. Thymine
43
Q

RNA

A

Ribonucleic Acid

Transfers genetic info from DNA -> ribosomes
- ribosomes read RNA
- make polypeptides (via translation)
Polymer of mononucleotide
- Pentose sugar (Ribose)
- phosphate group
- base variables
One polynucleotide strand
44
Q

RNA base variables

A
  1. Guanine
  2. Cytosine
  3. Adenine
  4. Uracil
45
Q

Sugar phosphate backbone

A

Mononucleotide joined via a condensation reaction

  • between phosphate group of one and sugar group of another
  • water = byproduct
46
Q

DNA structure

A

Double helix structure

  1. Two polypeptide strands joined via hydrogen bonds between bases
  2. Complementary base pairing:
    - A -T
    - C - G
    - equal amount of paid within molecule
  3. Hydrogen bonds between complementary pairs:
    - A - T = three
    - C - G = two
  4. Strands are anti parallel
  5. Twist -> anti parallel
47
Q

When was the double helix determined?

A

1953 by Watson and Crick

Previously protein was believed to hold genetic code as more chemically varied compared to DNA’s simplicity

48
Q

Gene

A

Sequence of mononucleotide bases on a DNA molecule that code for amino acids in a polypeptide

  • different proteins = different amino acid numbers + orders
  • order of mononucleotide bases in gene -> order of amino acids in protein
  • triplet = sequence of three bases that code for an amino acid
  • sequence of bases in DNA = template for proteins -> protein synthesis
49
Q

mRNA

A

Messenger RNA

  • made in nucleus during transcription
  • CODON = three adjacent bases
  • carries DNA genetic code from nucleus -> cytoplasm
50
Q

tRNA

A

Transfer RNA

  • located in the cytoplasm
  • amino acid binding site + sequence of three bases (ANTICODON) at either end
  • carries amino acids to ribosomes during translation
51
Q

DNA copied into RNA for protein synthesis

A

DNA molecules found in the nucleus
Organelles for protein synthesis (ribosomes) in cytoplasm
DNA = too large to move out of nucleus
Section is copied into mRNA = transcription
mRNA leaves the nucleus
Joins with ribosome in cytoplasm -> translation process

52
Q

Genetic code =

A

Non-overlapping:

  • sequence of base triplets/codons which code for specific amino acids
  • > triplet is read in sequence & do not overlap

Degenerate:

  • more possible triplet combos than amino acids
  • 20 amino acids
  • 64 triplets
  • some amino acids = 1+ triplet
  • > e.g. tyrosine = ‘UAU’ or ‘UAC’

Start + stop codons = production signals
- UAG = stop codon

53
Q

Transcription (protein synthesis)

A
  1. RNA polymerase attaches to DNA double helix at a gene’s start codon
  2. Hydrogen bonds between polypeptide strands in the gene break -> unwinds DNA
  3. Strand used as template for mRNA copy
    - RNA polymerase lines up free RNA mononucleotide alongside template
    - complementary bases paired (e.g. T -> U) -> complementary strand
    - RNA mononucleotide then joined by RNA polymerase -> mRNA
  4. RNA polymerase moves along DNA -> strands separate (mRNA assembled)
  5. Hydrogen bonds reform once RNA polymerase bases
    - strand winds up in double helix
  6. RNA polymerase reaches stop codon -> detaches from DNA
  7. mRNA moves out of nucleus via nuclear pore
    - attaches to ribosome in cytoplasm
54
Q

Translation (protein synthesis)

A
  1. mRNA attaches to ribosome
  2. tRNA carry amino acids to ribosome
  3. tRNA molecule (an anticodon = complementary to mRNA start codon) attaches to mRNA molecule
  4. Second tRNA attaches to next codon in chain via complementary base pairing
  5. Two amino acids on tRNA’s attached via peptide bonds
    - first tRNA detaches
  6. Ribosome moves onto next codon
  7. tRNA repeat process, producing chain of polypeptides until stop codon
  8. Polypeptide chain moves away from ribosome

Note: ribosome deals with two tRNA molecules at a time

55
Q

Semi-conservative replication

A

DNA copied before cell division
Half of DNA strands from each new helix are from the original
-> genetic continuity between generations

56
Q

Semi-conservative replication process

A
  1. DNA helicase breaks H-H bonds between bases on polynucleotide strands -> unwind
  2. Original strands act as templates -> complementary base pairing:
    - free floating DNA nucleotides attracted to complementary exposed bases
  3. Condensation reactions catalysed by DNA polymerase
    - nucleotides join
    - H-H bonds reform
  4. Each new DNA helix has one original polynucleotide strand & one new one
57
Q

Conservative Replication

A

Original DNA molecule stays together

58
Q

Genetic Mutations

A

Mutations = changes to base sequence of DNA
Caused by errors in DNA replication (usually):
- substitution = one base replaced with another
- deletion = one base is deleted
- insertion = extra base added
- duplication = one+ bases repeated
- inversion = base sequence reversed

Order of DNA bases -> order of amino acids -> primary structure of protein -> 3D shape

Causes Genetic disorders (lots of different mutations possible e.g. CF caused by 1,000+)

59
Q

Gene

A

A sequence of bases on a DNA molecule that codes for a protein which results in a certain charecteristic

60
Q

Allele

A

A different version of a gene; usually there are two types

61
Q

Genotype

A

The alleles a person has

62
Q

Phenotype

A

Charecterisitics displayed by an organism

63
Q

Dominant

A

Only one copy of an allele is needed to appear in the phenotype (R)

64
Q

Recessive

A

Two copies of the allele required to appear in phenotype (r)

65
Q

Incomplete dominance

A

Trait of a dominant allele is not completely shown over trait of recessive allele
Both alleles influence phenotype

E.g. snapdragons: red (RR), white (rr), pink (Rr)

66
Q

Homozygote

A

Organism copies two copies of same allele for a characteristic

67
Q

Heterozygote

A

Organism carries two different alleles for a characteristic

68
Q

Carrier

A

A heterozygote who has a recessive allele which is disease causing, but does not themselves have the disease

69
Q

Genetic diagrams

A

T t
T TT Tt
t Tt tt

= 50℅ Tt, 25℅ TT, 25℅ tt
3:1 genetic ratio for recessive phenotype

70
Q

Genetic Pedigree Diagrams

A

Ngng

71
Q

Cystic Fibrosis (CF)

A
  1. Caused by gene mutation that codes for CFTR protein
    - CFTR = Cystic Fibrosis Transmembrane conductance Regulator
  2. CFTR = channel protein
    - transports chloride ions out of cell -> mucus
    - causes H2O to move into mucus by osmosis -> watery
  3. Mutation -> less efficient at transport
    - mucus = thick + sticky
    - causes problems in: respiratory, digestive and reproductive systems
72
Q

CF + Respiratory system

A
  1. Mucus helps prevent lung infection -> traps microorganisms
    - transported to throat by cilia
  2. Cilia unable to move mucus (thick + sticky)
  3. Mucus builds in airways
  4. Some airways become completely blocked
    - > gas exchange cannot occur below blockage
  5. SA available for gas exchange reduced -> breathing difficulties
  6. More prone to lung infection
    - antibiotics -> stop microorganisms
    - physiotherapy -> dislodge mucus
73
Q

CF + digestive system

A
  1. Tube connecting pancreas to small intestine becomes blocked
    - > prevents digestive enzymes from reaching small intestines
    - > reduced digestive ability -> less nutrients absorbed
  2. Mucus can cause cysts to form in pancreas
    - > inhibit enzyme production
  3. Mucus lining in small intestine abnormally thick
    - > inhibits nutrients absorption
74
Q

CF + reproductive system

A
  1. Prevent production & transportation of gametes
  2. In men (usually):
    - tubes connecting testicles to penis are absent or blocked -> sperm has no access
  3. In women (usually):
    - thickened cervical mucus prevents sperm reaching egg (reduced sperm motility)
75
Q

Genetic screening - Identification of carriers

A

Informed decisions (having children + prenatal testing)
Social issues = finding a partner + emotional stress
Ethical issues =
- false results -> incorrect info etc
- employers/life insurance companies -> genetic discrimination

76
Q

Genetic screening - PGD

A

Pre-implantation Genetic Diagnosis

  • carried out on embryos produced by IVF
  • screening before implantation
  • avoids abortion + implantation of a genetically mutated embryo
  • issues: false results, finding out other characteristics (designer babies)
77
Q

Genetic Screening - Amniocentesis

A
  • 15 - 20 weeks of pregnancy
  • amniotic fluid sampled via abdomen ( v. Fine needle)
  • fluid contains fetal cells -> DNA
  • 1℅ risk of miscarriage
  • results = 2-3 weeks (conclusive), 3-4 days (basic)
78
Q

Genetic screening - Chorionic Villus Sampling (CVS)

A
  • 11-14 weeks of pregnancy
  • cells taken from chorionic villi via abdomen (needle)
  • or vagina (catheter = thin, flexible tube)
  • 1-2℅ risk of miscarriage
  • results = two+ weeks (in depth/detailed), few days (initial/obvious)
79
Q

Chorionic Villi

A

Villi that provide maximum contact area between the fetus and the mothers blood via the placenta

A Level Biology (SNAB) (10 decks)

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