A Level Biology Topic 2 Genes and Health notes

Cystic fibrosis
-​ Diff versions due to diff mutations of CFTR gene
-​ Affect liver, lungs, pancreas, spleen, skin, reproduction
-​ Liver and gallbladder: extra sticky bile blocks bile duct > irritation and
inflammation, scar tissue > liver disease
-​ Lung:
-​ Excess sticky mucus cause bacterial infection
-​ Mucus block bronchioles
-​ Less steep conc gradient, lower rate of gas exchange
-​ Let air pass in but not out: overinflation of lung tissue,
reduced elasticity
-​ Airway clearance, antibiotics
-​ Pancreas: mucus blocks delivery of digestive enzymes to digestive system,
protease break down islets of langerhans, trouble producing insulin and
digestive enzymes > type 1 diabetes
-​ Pancreatic enzyme pills (gastro-resistant to low pH)
-​ Need high fat + calorie intake: partial digestion and malabsorption
-​ Saltier skin: faulty secretory cell of sweat glands, sweat glands cannot
reabsorb salt from sweat
-​ Reproduction: infertility
-​ Mucus block vas deferens / congenital bilateral absence of the vas
deferens CBAVD
-​ thicker vaginal mucus plug, harder for sperm to reach ovum

Endocrine glands Exocrine glands

Pituitary gland, thyroid gland, adrenal glands, Pancreas, salivary glands, gastric glands: sweat,
pancreas: secrete hormones to regulate body tears, saliva, milk and digestive juices
-​ With ducts >> get blocked by mucus
functions
-​ Richly supplied w blood capillaries
-​ Ductless: secrete hormones directly
into blood


Pancreas: endocrine gland regulate blood glucose level by secreting insulin + glucagon into
blood

, ●​ Also exocrine gland: acinar cells secrete pancreatic juice w digestive enzymes
(pancreatic amylase, proteases, lipase) via pancreatic duct for digestion




Mutations
-​ Sudden and permanent change in DNA of an organism


Causes of mutations
1.​ Spontaneous mutations
a.​ Occur naturally and randomly at a very low rate (esp @DNA replication)
2.​ Induced mutations by mutagens
a.​ Chemical: change chemical structure of DNA
i.​ Nitrous acid (food preservatives): change base of DNA molecule
ii.​ Tar (cigarette smoke)
iii.​ Asbestos (construction materials)
iv.​ Mustard gas (chemical warfare)
b.​ Radiation
i.​ UV light (sunlight)
ii.​ X-rays (medical examination): ionise water or other molecules to form
free radicals (highly reactive, can damage DNA molecules)

, iii.​ Gamma rays (radiotherapy, nuclear bombs): ionise water or other
molecules to form free radicals (highly reactive, can damage DNA
molecules)


Types of mutations

Gene mutations Chromosome mutations

-​ Changes in base sequence of DNA -​ Changes in structure/number of
on a gene chromosomes
-​ Occur @DNA replication -​ Occur @
-​ Produce new alleles in a population
Change in chromosome structure
POINT MUTATION -​ Affect some genes: death of
Substitution and inversion embryos/foetuses before birth
-​ usually change in 1 triplet code only -​ @crossing over of non sister
-​ Possibilities chromatids in meiotic cell division
a.​ Silent mutation: new code -​ Possibilities
specifies the same amino acid: X -​ Deletion
effect on AA sequence -​ Duplication: segment is
b.​ Missense mutation: new code repeated
specifies a diff amino acid: 1 -​ Inversion: broken segment
diff amino acid: change of protein reversed order, reinserted
structure in non-critical area / -​ Translocation: crossing over
critical area (alter 3D structure of chromatids of non
of protein> non functional) homologous chromosomes
c.​ Nonsense mutation: new code
specifies a stop signal: Change in chromosome number
polypeptide production stopped -​ Addition of loss of many genes per
prematurely > non functional chromosome: most die before birth
-​ @anaphase I, II in meiotic cell
FRAMESHIFT MUTATION division
Deletion and insertion -​ Nondisjunction: homologous pair of
-​ Often dramatic effect chromosomes or sister chromatids
-​ Possibilities fail to separate, go to same
-​ Delete/insert Xmul3 bases: daughter cell > abnormal no of
shift reading frame, whole chromosomes
AA sequence after point of
mutation altered > non <extra chromosome 21> down syndrome
functional -​ Risk increases with mother’s age
-​ @meiosis: 2 members of homologous

, <substitution> sickle cell anaemia chromosome 21 fail to separate,
-​ (2 mutated alleles) Substitution of gamete bearing extra chromosome
base in gene coding for polypeptide fuse with normal gamete
chain in haemoglobin: -​ Symptoms
-​ base T replaced by base A -​ Shorter than avg
-​ 1 diff amino acid (valine -​ Distinctive round face with
instead of glutamic acid) smaller ears
-​ affect shape of polypeptide -​ Some degree of mental
formed, properties of retardation
protein -​ Most die @early childhood due to
-​ Low O2 levels: abnormal infections, heart defects
haemoglobin molecules less soluble,
stick tgt, form long fibres, distort <missing X chromosome: XO> turner’s
shape of RBCs (sickle shaped) syndrome
-​ Decrease O2 carrying -​ Female
capacity of RBCs -​ Little development of secondary
-​ Clump tgt, block capillaries > sexual characteristics
easy bruising, damage organs -​ Infertile: X ovaries, menstruation
-​ RBCs have shorter life span
> anaemia <extra X chromosome: XXY> klinefelter’s
syndrome
-​ Male
-​ Some degree of breast development
-​ Infertile: testes underdeveloped




<common: phenylalanine (AA) deletion> cystic fibrosis
-​ Cystic fibrosis transmembrane regulator (CFTR) non functional / absent
-​ Transmembrane/integral protein
-​ Ligand-gated chloride channel: facilitated diffusion
-​ ATP and phosphate bind to CFTR to open/close gate
-​ Cl- travel down conc gradient (unidirectional: Cl- leave cell)
-​ CFTR closed = ENaC always opened
-​ Epithelial sodium channel (unidirectional: Na+ enter cell)
-​ >> ATP temporarily builds in cell
-​ Decreased conductance: X transport Cl- ions out across cell membrane to lower
water potential
-​ Water and Na+ X move out by osmosis
-​ Mucus become thick, sticky >> accumulation