Stem Cells

differentiation?

the process of cells becoming specialised

Despite being differentiated in structure and function, what do all body cells in an organism have the same?

have the same DNA (except those without a nucleus - erythrocytes and sieve tube elements)

What does differentiation involve the expression of?

some genes but not others in the cells genome

What do all cells in plants and animals begin as?

undifferentiated cells

What do all cells in plants and animals originate from?

mitosis or meiosis

Stem Cells?

undifferentiated/unspecialised cells - not adapted to any function

What do stem cells have the potential to do?

differentiate to become any one of the range of specialised cells in the organism

What are stem cells the source of?

the source of new cells necessary for growth, repair and development

How many times can stem cells undergo cell division?

again and again

What happen once stem cells become specialised?

they lose their ability to divide - entering G0 phase of the cell

What needs to be strictly controlled?

the activity of stem cells

What happens when stem cells don't divide fast enough?

tissues aren't efficiently replaced, leading to ageing

What happens if there is uncontrolled division of stem cells?

form masses of cells - called tumours - which can lead to the development of cancer

Potency?

a stem cells ability to differentiate into different cell types

Greater potency?

the greater the number of cell types it can differentiate into

Totipotent?

these stem cells can differentiate into any type of cell

Examples of totipotent cells?

fertilised egg and the 8 or 16 cells from its first mitotic divisions

What is a fertilised egg destined to eventually produce?

a whole organism

What can Totipotent cells also differentiate into?

extra-embryonic tissues

Examples of extra-embryonic tissues (2)?

amnion and umbilicus

Pluripotent stem cells?

can form all tissue types but no whole organisms

Where are Pluripotent stem cells present?

early embryos

What are Pluripotent stem cells the origin of?

different types of tissue within an organism

Multipotent stem cells?

can form a range if cells within a certain type of tissue

Example of a Multipotent stem cell?

haematopoetic stem cells in bone marrow

Why are haematopoetic stem cells multipotent?

gives rise to the various type of blood cells

How have multicellular organisms (animals and plants) evolved from unicellular (single-celled) organisms?

groups of cells with different functions working together as one unit can make use of resources more efficiently than single cells operating on their own

What do cells have do to in multi-cellular organisms to take on different roles in tissues and organs?

have to specialise

Cells present in the blood?

erythrocytes and neutrophils

Why do erythrocytes and neutrophils look very different?

they have different functions

What happens when cells differentiate?

they become adapted to their specific role

What are all blood cells derived from?

stem cells in the bone marrow

What are mammalian erythrocytes adapted to maximise?

their oxygen-carrying capacity by only having few organelles - more room for haemoglobin (their role is to transport oxygen around the body)

Lifespan of erythrocytes?

short life span - 120 days

Why do erythrocytes have short lifespans?

lack of nucleus and organelles

What does them have a short lifespan means has to happen?

need to be replaced constantly

How many erythrocytes do the stem cell colonies produce per day to keep up with the demand?

around 3 billion erythrocytes per kilogram of body mass per day

What do neutrophils have an essential role in?

the immune system

How long do neutrophils live for?

around 6 hours

How many neutrophils are produced per hour by colonies of stem cells in bone marrow?

1.6 per kg of body mass per hour

When does this figure increase?

during infection

Sources of animal stem cells?

embryonic stem cells and tissue (adult) stem cells

What is the potency of embryonic stem cells?

totipotent

When are embryonic stem cells present?

at a very early stage of embryonic development

What is formed after seven days from embryonic stem cells?

a mass of cells - called a blastocyst

What is the potency of embryonic stem cells after forming a blastocyst?

pluripotent

How long do embryonic stem cells remain in a pluripotent state for in the fetus?

until birth

When are tissue (adult) stem cells present?

throughout life from birth

Where are tissue (adult) stem cells found?

specific areas - bone marrow

Potency of tissue (adult) stem cells?

multipotent

What is there some evidence that tissue (adult) stem cells could be triggered to become?

pluripotent

Where can stem cells also be harvested from?

the umbilical cords of new born babies

Advantages of the umbilical cord as a source of stem cells?

plentiful supply of umbilical cords and invasive surgery is not needed

Why can these stem cells be stored?

in case they are ever needed by the individual in the future

Why can these stem cells be used if needed by the individual in the future?

tissues cultured from such stem cells wouldn't be rejected in a transplant to the umbilicus' owner

Sources of plant stem cells?

meristematic tissue (meristems)

Where is meristematic tissue found?

wherever growth is occurring in the plants - e.g. the tips of the roots and shoots

What are the tips of roots and shoots called?

apical meristem

Where else is meristematic tissue located?

sandwiched between phloem and xylem tissues

What is the meristematic tissue that is sandwiched between phloem and xylem tissues called?

vascular cambium

what do cells originating from this region differentiate into?

different cells present in the xylem and phloem tissues

What continues throughout the life of the plant?

the pluripotent nature of the stem cells

What grows as the plant grows?

the vascular tissue - due to the vascular cambium

Uses of stem cells: heart disease - what is damaged as a result of a heart attack?

muscle tissue in the heart

Uses of stem cells: heart disease - what has been tried experimentally?

to repair muscle tissues in heart - some success

Uses of stem cells: type 1 diabetes - why are stem cells needed?

the body’s own immune system destroys the insulin producing cells in the pancreas - patients have to inject insulin for life

Uses of stem cells: Parkinson's disease - what are its symptoms caused by?

(shaking and rigidity) - the death of dopamine-producing cells in the brain

Uses of stem cells: Parkinson's disease - what can drugs for it only currently do?

delay the progress of the disease

Uses of stem cells: Alzheimer's - what are brain cells destroyed as a result of?

the build up of abnormal proteins 0 drugs only alleviate the symptoms

Uses of stem cells: macular degeneration - what is it responsible for?

causing blindness in the elderly and diabetics - scientists currently researching the use of stem cells in its treatment

Uses of stem cells: birth defects - what have scientists already successfully reversed?

previous, untreatable birth defects in model organisms - mice

Uses of stem cells: spinal injuries - what have scientists restored?

some movement to the hind limbs of rats with damaged spinal cords using stem cell implants

Stem cells used: the treatments of burns - what can produce new skin for burn patients?

stem cells grown on biodegradable meshes

Stem cells used: the treatments of burns - what is this treatment quicker than?

taking a graft from another part of the body

Stem cells used: drug trials - what can potential new drugs be tested on?

cultures of stem cells before being tested on animals and humans

Stem cells used: developmental biology - why have stem cells become an important area of study in biology?

due to their ability to divide indefinitely and differentiate into almost any cell without the organism

Stem cells used: developmental biology - what is developmental biology?

the study of changes that occur as multicellular organisms grow and develop from a single cell (and why this sometimes go wrong)

What have stem cells been used in medicine in the form of for many years?

bone marrow transplants

What where the embryos that were used originally from?

those left over by fertility treatment

The law has change so that embryos can be specifically created where?

in the laboratory as a source of stem cells

What does the removal of stem cells from embryos result in?

the destruction of embryos

Although what is being developed?

techniques that allows stem cells to be removed without damage to embryos

What objections are there to the use of embryos?

moral and religious

Where do many people believe life begins?

at conception - so the destruction of embryos is murder

What is this controversy holding back?

progress that could lead to the successful treatment of many incurable diseases

Why is the usefulness of umbilical cord stem cells limited (2)?

multipotent (not pluripotent like embryonic stem cells) and more likely to have acquired mutations

Why are adult tissue stem cells not as good as embryonic stem cells?

don't divide as well

What doesn't raise the same ethical issues as animal cells?

the use of plant stem cells

What are developments being made towards?

artificially transforming tissue stem cells in pluripotent cells

What are induced pluripotent stem cells (iPSCs)?

adult stem cells that have been genetically modified to act like embryonic stem cells - so they are pluripotent