Block B Lecture 3 - Ageing Flashcards
What are 5 properties of aged cells?
Examples Include:
Slow division
Change in cellular metabolism (decrease basal rate and slowing of all chemical reactions)
Change in cellular function
Inability to carry out apoptosis
Decreased sensitivity of all receptors
Reduced ability to withstand ROS
DNA Instability (Note - may lead to a cancerous growth forming)
(Slide 3)
What are 3 signs that we are programmed to die?
The Hayflick limit of cell division
Telomere shortening
Insulin/IGF-1 signalling via FOXO transcription factor deficits occurring with age
Reduced immunity over time
(Slide 4)
How did Leonard Hayflick prove the existence of the Hayflick Limit?
- He isolated and cultured fibroblasts cells from human tissue, an placed them in a culture vessel with a nutrient medium
- Cells then divide and form a confluent layer on vessel surface
- He then discarded half of the cells, allowing the remainder of them to grow back to confluency - this is known as a passage
- Passages are repeated
- Cell replication is observed to slow, and eventually it stops after about 50 (+ or - 10) passages.
- Cells have reached the Hayflick limit and undergone replicative senescence
(Slide 5)
What is a confluent layer?
It means that cells have grown to cover the entire surface of the culture dish
(Slide 5)
What is the function of telomeres?
To protect the ends of chromosomes from damage
(Slide 6)
What repeated nucelotide sequence do telomeres contain?
TTAGGG
(Slide 6)
What happens to telomeres as cells divide?
The gradually shorten, until eventually cell division stops once they run out
(Slide 6)
What kind of protein is telomerase?
A ribonucleoprotein (a protein containing both RNA and protein molecules)
(Slide 7)
What are the 2 main components of telomerase?
Telomerase reverse transcriptase (hTERT) protein and the hTR RNA (aka TERC) component
(Slide 7)
What are the functions of the telomerase reverse transcriptase (hTERT) protein and the hTR RNA component contained in telomerase?
the hTERT protein contains the catalytic component whereas the hTR RNA component provides the template for telomere synthesis
(Slide 7)
What does telomerase do?
It adds the telomere repeats (TTAGGG) onto the ends of chromosomes
(Slide 7)
What differentiated cells usually don’t express telomerase?
Differentiated somatic cells
(Slide 7)
Is telomerase expressed in stem cells?
Yes
(Slide 7)
How are cancer cells able to divide uncontrollably and infinitely?
As telomerase becomes reactivated in these cells, allowing it to add to the ends of telomeres and divide without limit
(Slide 7)
What are 2 issues with trying to reverse ageing with telomerase?
It may lead to an increased risk of tumours
It may not even work! E.g mouse tissue has active telomerase but mice aren’t immortal
(Slide 8)
What are 5 signs that we die because “we are worn out”?
Answers Include:
The Wear-and-tear theory
Metabolic “rate-of-living” aka “burn-out”
Nutrients / Diet
Mitochondrial dysfunction
Free radical generation
Oxidative Stress / accumulated cellular and DNA damage
(Slide 9)
What does the “Rate-of-living” theory state?
“The duration of life varies inversely as the rate of energy expenditure increases” - in other words the length of life depends on the rate of living.
(Slide 10)
What is an example of an experiment which backs up the “rate-of-living” theory?
- Drosophila flies were kept in confinement under different temperatures
- Flies kept in higher temperatures were observed to have a shorter lifespan
- It was theorised that this is because a higher temperature increases the metabolic rate of the flies
^ “the length of life depends on the rate of living”
(Slide 10)
What is the free radical / superoxide theory of ageing?
Free radicals are by-products of mitochondrial respiration, with excessive ROS or RNS eventually leading to the damage of cellular components, such as DNA, proteins and lipids
(Slide 11)
What are 2 examples of oxygen free radicals?
Answers Include:
Superoxide
Hydroxyl
Peroxyl
Alkoxyl
Hydroperoxyl
(Slide 11)
What organism is used as a model of aging?
Drosophila flies
(Slide 13)
What is the mechanism that results in an decreased essential amino acid consumption and what is it mediated by?
Its mediated by TOR signalling, if there isn’t an adequate amount of nutrients then autophagy (consumption of the body’s own tissue as a metabolic process occurring in starvation and certain diseases) increases, and cell growth and protein synthesis decreases leading to an extended life
(Slide 12)
What happens when you connect the circulatory systems of old and a young mouse together?
The heart size of the old mouse decreases whereas the heart size of the young mouse increases
Note: debated whether this is de-aging or just rejuvenation of stem cell niche
(Slide 15)
What are 3 causative factors for aging?
Growth Differentiation Factor 11
CCL11
Oxytocin
(Slide 17)