1 - Ageing Flashcards
(31 cards)
What is the biological definition of ageing
Ageing is a decline in biological function over time, characterised by increasing mortality and decreasing reproductive success with advancing age.
Often used synonymously with senescence
What determines an individual’s rate of ageing and potential lifespan
A combination of extrinsic (environmental) and intrinsic (genetic) factors, which don’t directly cause ageing but influence its evolution
Name examples of extrinsic causes of death that influence ageing evolution
Predation, accidents, fatal disease, starvation, extreme temperatures, drowning
How does high extrinsic mortality affect evolution of ageing
It reduces natural selection pressure for longevity and favours early reproduction
Name extrinsic factors that accelerate or decelerate ageing
Lifestyle (smoking, diet, exercise), environmental pollution (toxins, radiation), stressors in non-human animals (e.g., competition, habitat changes)
How does temperature affect lifespan in ectotherms
Chronic heat exposure shortens lifespan, chronic cool exposure extends it, and acute heat shock may extend lifespan by elevating heat-shock proteins (HSPs) that protect against protein damage
What is known about caloric restriction (CR) in humans
Some people reduce calorie intake by ~30% (CR Society).
It might increase lifespan by 1–5 years, but this is unproven and difficult to maintain long-term
What intrinsic (biological) mechanisms affect ageing
Genes that regulate reproduction, body maintenance, and repair.
Mutations can accelerate or slow ageing. Ageing rate = Genes × Environment
What are the three main ways to measure ageing
Mortality rate (increase in death with age)
Reproductive success (decline in fertility)
Physiological decline (reduced organ/cell function)
Describe ageing in different organisms
Humans: Complex; affected by genes, lifestyle, medicine
Non-human mammals: Age slower/faster than humans (e.g. Greenland shark ages very slowly)
Reptiles (e.g. turtles): Show negligible senescence
Plants: Some reverse ageing or live thousands of years
Why is the hydra considered potentially immortal
No evidence of ageing
Regenerates from small tissue pieces
Reproduces by budding, avoiding senescence
What’s the difference between unitary and modular organisms in ageing
Unitary organisms follow classic ageing.
Modular organisms may show little to no ageing as they can regenerate lost parts
Why does ageing evolve, despite natural selection favouring survival and reproduction
Due to evolutionary trade-offs and declining selection pressure with age
Mutation Accumulation
(Medawar, 1952) – Late-acting harmful mutations accumulate as selection weakens with age (e.g. Huntington’s)
Antagonistic Pleiotropy
(Williams, 1957) – Genes beneficial early in life are harmful later (e.g. BRCA1/2)
Disposable Soma
(Kirkwood, 1977) – Energy favours reproduction over maintenance
Hyperfunction Hypothesis
(Blagosklonny) – Overactive growth pathways in later life cause age-related disease (e.g. cancer, hypertension)
Are any of the evolutionary theories of ageing definitively correct
They complement each other:
Mutation Accumulation & Antagonistic Pleiotropy = focus on reduced selection
Disposable Soma & Hyperfunction = focus on trade-offs and overactivity
What is Peto’s Paradox
Despite having more cells and longer lives, large animals don’t have higher cancer rates
Suggests evolution of enhanced cancer suppression mechanisms
How do large/long-lived animals suppress cancer - Elephants
20 copies of TP53 (vs 1 in humans); enhances DNA repair/apoptosis
How do large/long-lived animals suppress cancer - Bowhead whales
Mutations in ERCC1 (DNA repair gene), low cancer rates
How do large/long-lived animals suppress cancer - naked mole rats
High molecular weight hyaluronan prevents tumour spread
How do large/long-lived animals suppress cancer - dogs vs humans
Dogs have higher cancer despite being smaller, so resistance varies
What does research in model organisms reveal about ageing genes
Age-regulating genes and pathways are conserved across species
