Topic 2 - Genes and Health Flashcards
Fick’s Law equation
Rate of diffusion ∝ (surface area × difference in concentration)/diffusion surface thickness
Fick’s Law
Diffusion is faster when surfaces have a large area and are thin
The steeper the concentration gradient, the faster diffusion will be
Respiration
A process in living organisms involving the release of energy from breakdown of glucose. It occurs within cells.
Ventilation
The movement of air into and out of the lungs to supply oxygen to the body and remove carbon dioxide
Breathing
The action performed by the diaphragm and the intercostal muscles to allow ventilation
Gas exchange
The movement of gases by diffusion into and out of the blood from the alveoli. Carbon dioxide diffuses into the alveoli, whilst oxygen diffuses out
Alveoli adaptations
- shape
- large number
- numerous capillaries
- thin walls made of epithelial cells
- constant flow of blood through capillaries
- ventilation
- surfactant
Shape of alveoli (adaptation)
Increases surface area to maximise the volume of oxygen diffusing into the blood and the volume of carbon dioxide diffusing out
Numerous alveoli (adaptation)
Increases surface area to maximise gas exchange
Numerous capillaries (adaptation)
Increases SA for gas exchange
Thin walls made of epithelial cells (adaptation)
Reduces diffusion distance for gases to increase the rate of diffusion
Constant flow of blood through capillaries (adaptation)
Maintains steep concentration gradient
Ventilation (adaptation)
Makes sure that gas exchange can take place and maintains steep concentration gradient
Surfactant (adaptation)
- helps moisten the walls of the alveoli so that gases can easily dissolve and diffuse
- lowers surface tension, thereby preventing the alveoli from collapsing during breathing, which maintains high SA
What are proteins made of?
- elements: carbon, hydrogen, oxygen, nitrogen
- polymers made from monomer units called amino acids
- there are 20 different amino acids, which can be arranged in different orders to give a variety of different proteins
General structure of amino acid
a central carbon atom attached to a hydrogen, an acidic carboxyl group (−COOH), an amino group (−NH2) and an organic side chain (also called an R group)
*refer to diagram
Significance of R group in amino acid
- determines what amino acid it is and how it interacts
- R-groups give each amino acid its own specific characteristics e.g. size, polarity, pH
Protein
One or more polypeptide chains folded into a highly specific 3D shape. There are up to four levels of structure in a protein.
Primary structure
The sequence of the amino acids in a polypeptide chain
- peptide bonds
- it determines the order of amino acids, which determine the order of the R groups
Secondary structure
A regular, repeating 3D structure. Either coils into an alpha helix or a beta-pleated sheet
- hydrogen bonds
- α-helix: flexible and elastic
- β-pleated sheet: stable and strong
Tertiary structure
When the primary and secondary structures are folded further into mored complicated 3D shapes. Determined by R-group
- hydrogen bonds, disulfide bridges, ionic bonds
- gives protein its unique shape and function
Quaternary structure
Two or more polypeptide chains linked together to form one large, complex protein. Not all proteins are made of more than one chain, so not all proteins have quaternary structure
- hydrogen bonds, disulfide bridges, ionic bonds
- contributes to overall 3D structure of protein
- may contain inorganic additions that aid function (e.g. haem group)
Globular proteins features
- polypeptide chain is folded into spherical and compact shape
- soluble due to hydrophilic side chains on outside of protein
- hydrophilic side chains can form weak hydrogen bonds with water, allowing them to dissolve
- typically used in metabolic functions
Haemoglobin (case study)
- Function: carry oxygen to the tissues for respiration
- conjugated protein - has a haem prosthetic group (non-protein)
- haem group contains an iron ion, which gives haemoglobin its red colour + carries oxygen
- consists of 4 polypeptide units (2x alpha chains, 2x beta chains)
- CO has higher affinity for haemoglobin than oxygen
Fibrous proteins features
- remain as long chains
- insoluble, as amino acids on outside are hydrophobic (repel water)
- several polypeptide chains can be cross-linked for additional support
- these strong molecules have structural roles
Collagen (case study)
- helices
- 3 polypeptide chains around each other
- hydrogen bonds form between chains to hold them together
- high tensile strength - provides mechanical strength in the walls of arteries + makes up tendons, bones and cartilage
Collagen fibril
The structure formed due to covalent bonds between collagen molecules (cross links)
Pancreas
Organ that secretes most digestive enzymes. Important part of the exocrine and endocrine system.
Small intestine (notes)
- villi to increase SA
- absorption of small molecules broken down in the stomach
Protease (notes)
- pepsin in stomach (proteins -> amino acids, breaks peptide bonds in hydrolysis)
- trypsin in small intestine
Lipase (notes)
lipids -> 3x fatty acids + glycerol
Amylase (notes)
- starch -> maltose
- salivary glands into mouth
- pancreas into small intestine
Anabolic
pathway that requires energy and is used to build up large molecules from smaller ones
Catabolic
pathway that releases energy and is used to break down large molecules into smaller ones
Endocrine
a system of ductless glands that release hormones into the blood to regulate body functions
Exocrine
Produce and secrete substances via a duct onto an epithelial surface. Relating to enzymes.
Lock and Key model
- shape of substrate (key) exactly fits the active site of the enzyme (lock) - complementary
- the enzyme holds the substrate in a particular way that will allow reaction to take place easily
Induced fit model
- substrate is not a perfect match to the active site
- a specifically shaped substrate will cause the active site to change shape
- this puts strain on the bonds, causing the substrates to react
Activation energy
the minimum quantity of energy needed to start a reaction
How enzymes reduce activation energy
- the active site has electrically charged groups
- attraction of oppositely charged groups can distort shape of substrate
- the breaking/formation of bonds is aided
- some active sites may contain amino acids with acidic side chains to provide favourable reaction conditions
Decarboxylase
- removal of carboxyl group in respiration with formation of CO2
- intracellular
- catabolic
Maltase
- breakdown of maltose -> glucose
- extracellular
- catabolic
DNA polymerase
- joins nucleotides together in DNA replication
- intracellular
- anabolic
Catalase
- breakdown of hydrogen peroxide
- extracellular
- catabolic
Pancreatic lipase
- breakdown of triglycerides into glycerol + fatty acids
- extracellular
- catabolic
Measuring rate of enzyme reaction
- measure how much substance is produced in given time
- measure how quickly the substrate is used up
How to calculate initial rates from graph
- draw tangent to curve for initial section of curve
- calculate rate of change (Δy/Δx)
- work out units
Inhibitor
substance that slows down enzyme activity
- competitive or non-competitive
Competitive inhibitor
- competes for same active site as substrate
- more substrate = lower effect of inhibitor
Non-competitive inhibitor
- binds somewhere else of globular protein/enzyme
- changes structure of enzyme so that it no longer catalyses
Endocytosis
- uptake of substances
- a large structure is surrounded by the cell membrane and engulfed in a vesicle, which moves into the cell
- requires energy in the form of ATP
Exocytosis
- export of substances
- large molecules in the cell are engulfed in a vesicle
- the vesicle then moves to the cell membrane where it fuses with the membrane
- the contents are released out of the cell
- requires energy in the form of ATP
Mononucleotide structure
- phosphate group (circle)
- pentose sugar (deoxyribose or ribose)
- nitrogenous base (rectangle)
Peptide bond
Carboxyl group of one amino acid joins to the amino group of another
Properties of gas exchange surfaces
- large surface area to volume ratio
- thin surface
- steep concentration gradient maintained
How the lungs are adapted for rapid gas exchange
- have large surface area due to presence of many alveoli
- good supply of circulating blood to the lungs ensures that concentration gradient of carbon dioxide and oxygen is steep
- high concentration of oxygen and low concentration of carbon dioxide is maintained by mechanical ventilation
- short diffusion distance as alveoli walls are one cell thick
osmosis
the net movement of water molecules from a solution with more free water molecules to a solution with less free water molecules through a partially permeable membrane
passive transport
the fundamental movement of ions and other molecular substances within the cells along the concentration gradient, without any external energy
examples: diffusion, facilitated diffusion, osmosis
active transport
the process in which substances are pumped across a membrane against a concentration gradient using ATP
carrier proteins
move large molecules into or out of the cell, down their concentration gradient
channel proteins
form pores in the membrane for charged particles to diffuse through - down the concentration gradient
DNA facts
bases: adenine, thymine, cytosine, guanine
sugar: deoxyribose
bonding:
- phosphodiester bonds between phosphate group and C5
- hydrogen bonds between bases
structure: alpha double helix with a sugar-phosphate backbone on each strand
polynucleotide composed of mononucleotides joined by condensation reactions
mRNA facts
bases: adenine, cytosine, guanine, uracil
sugar: ribose
bonding:
- phosphodiester bonds between phosphate group and C5
- hydrogen bonds between bases
structure: single-stranded, not usually folded, carries codons which attach to tRNA via hydrogen bonds
tRNA facts
bases: adenine, cytosine, guanine, uracil
sugar: ribose
bonding:
- phosphodiester bonds between phosphate group and C5
- hydrogen bonds between bases
structure: single-stranded, folded into a specific structure held together by hydrogen bonds, carries anticodons complementary to mRNA codons bonded via hydrogen bonds
cell membrane components
- proteins (peripheral, integral)
- cholesterol
- glycolipids
- glycoproteins
nature of genetic code
- triplet code
- degenerate
- non-overlapping
- universal
triplet code
the three letter code that determines the sequence of bases found within a gene
three bases = codon = one amino acid
non-overlapping
each base is only read once
degenerate
multiple codons can code for the same amino acids
universal
almost every organism uses the same code
gene
a sequence of bases on a DNA molecule that codes for a sequence of amino acids in a polypeptide chain
transcription
- RNA polymerase binds to the promotor region ahead of the gene
- DNA is unzipped as hydrogen bonds between complementary bases break
- template strand provides complementary code for mRNA. Free RNA nucleotides join with the complementary bases with temporary hydrogen bonds
- phosphodiester bonds form between mRNA nucleotides
- mRNA detaches from template strand
- the two DNA strands join together
- DNA molecules wind back up into a helix
- mRNA leaves nucleus via nuclear pores
translation
- temporary hydrogen bonds form between anticodon of tRNA and complementary codon of mRNA
- attached to the tRNA is the amino acid
- this always starts with a start codon (AUG)
- ribosome moves along the length of mRNA
- another tRNA brings along another amino acid
- peptide bonds joins amino acids together
- protein synthesis stops when stop codon is reached
- mRNA is recycled and protein is folded with the help of chaperone proteins
antisense strand
the DNA strand used as a template to make the mRNA molecule
enzyme
biological catalysts that reduce activation energy
DNA replication steps
- gyrase unwinds DNA
- helicase unzips the helix by causing the hydrogen bonds to break
- DNA nucleotides align with their complementary base (on both strands)
- DNA polymerase joins the adjoining nucleotides together by catalysing the phosphodiester bond
Meselson and Stahl’s experiment
- DNA was originally grown in N15 for several generations so that all bases contained this isotope
- DNA was then grown in N14 for a generation
- after this generation, the DNA had one strand containing N15 and another strand containing N14
- after another generation, half of the DNA molecules were the same as generation 1, and the other half contained entirely N14
Mutation
a rare, random change in the sequence of base pairs in a DNA molecule that may result in an altered polypeptide
Types of gene mutations
- substitution (change in one base)
- insertion (adding another base in)
- deletion (taking a base out)
- duplication (adding the same base more than once)
- inversion (swapping the order of bases around)
how CF affects the respiratory system
- build-up of mucus in lungs traps bacteria, increasing risk of infection
- build-up of mucus in airways decreases surface area of alveoli exposed to air, reducing surface area for gas exchange
how CF affects the reproductive system
- cervical mucus prevents sperm from reaching the egg
- in men, sperm duct is blocked by mucus, meaning sperm cannot leave testes
how CF affects the digestive system
- pancreatic duct blocked by mucus, so digestive enzymes cannot reach small intestine
- food is not properly digested, so fewer nutrients absorbed
- mucus lining in duodenum is thick, reducing absorption of nutrients
- mucus can form cysts in pancreas, inhibiting production of enzymes and therefore digestion
Allele
different version of the same gene
Genotype
all the alleles of an organism
Phenotype
the set of observable characteristics of an individual resulting from the interaction of its genotype with the environment
Recessive
an allele that produces a feature only if two copies are present
Dominant
an allele that produces a feature even if only one copy is present
Incomplete dominance
a form of gene interaction in which both alleles of a gene are partially expressed, often resulting in an intermediate or different phenotype
Homozygote
an individual having two identical alleles of a particular gene
Heterozygote
an individual having two different alleles of a particular gene
Pedigree rules
- dominant disorders can’t jump generations but recessive ones can
- it is impossible for two people with a recessive disorder to have children without the disorder
- it is possible for two people with a dominant disorder to have children without the disorder
Preimplantation genetic diagnosis (PGD)
embryos created through IVF are tested for genetic disorders before they are implanted in the woman’s uterus
Chorionic villus sampling
- carried out at 8-12 weeks of pregnancy
- a sample of embryonic tissue is taken from the placenta and the DNA is analysed
- quicker than amniocentesis
Amniocentesis
- carried out at 14-16 weeks
- a sample of amniotic fluid containing foetal cells is obtained using a needle
- the DNA is then analysed
- results are available after 2-3 weeks, as foetal cells need to be grown in culture first
Social and ethical issues surrounding genetic testing
- risk of harm to foetus or miscarriage
- outcome of testing may lead to abortion
- cost of bringing up baby with genetic disorder
- emotional and mental issues surrounding caring for a baby with a genetic disorder
