4ABCD

**Autocrine Signalling**

signals that act on the cell that secreted them

**Paracrine Signalling**

signalling molecules that act on cells that are close by

**Endocrine Signalling**

signalling molecules that act on cells that are far from the gland/organ

Types of Hormones

Peptides (proteins), Steroids (lipids)

Ways cells communicate w/ each other

Hormones, Neurotransmitters, Cytokines, Pheromones

Cytokines

•Involved in communication between immune cells

•Regulating inflammation

•Response to cell damage or pathogens (autocrine or paracrine)

•Fighting infection

Pheromones

Signalling that is excreted into the external environment

Influence behaviour or physiology of another organism (unconscious communications)

E.g. triggering aggressive behaviour, attracting a mate, food trails

Stimulus Response Model (Cells)

Signalling molecule → reception → Transduction → Cellular response

Transduction

Converting the signal in a form that can be relayed to its final destination (can be one step or many)

Compare and contrast hormones and neurotransmitters

Hormones: Hormones are produced in endocrine glands and are secreted into the blood stream. Neurotransmitters: Neurotransmitters are released by presynaptic nerve terminal into the synapse.

Hormones: have stronger effects but are slower, Neurotransmitters: have weaker effects but are faster

Hormones: act on distant target cells (endocrine signalling)

Neurotransmitters: act on cells close by (paracrine signalling)

Why would multi cellular organisms have different types of cell signalling?

multicellular organisms, cell signaling allows for specialization of groups of cells.

compartmentalisation

By concentrating the necessary components inside a small region within the cell, cell compartmentalization improves the efficiency of several subcellular activities. Intracellular membrane systems create enclosed compartments separated from the cytoplasm of the cell.

Cells replicate exponentially

after each round of replication the number of cells present doubles

Purposes of cell division

**Growth and Development**

As we grow larger, our cells don’t actually become larger. Instead, we are simply made of more cells. Therefore, for a multicellular organism to grow and develop, it is important that cells replicate.

**Maintenance and Repair**

Cells are constantly dying as they age or become damaged. Cell replication allows these cells to be replaced

**Reproduction**

Prokaryotic and eukaryotic cells replicate to reproduce. When they replicate, they are enlarging their population.

Binary Fission Step 1

A prokaryotic cell before binary fission

Binary Fission Step 2

The circular chromosome is uncoiled and is replicated. Plasmids are replicated too

Binary Fission Step 3

The cell elongates to prepare for cell division

Binary Fission Step 4

Cell undergoes cytokinesis in which the cell pinches inwards creating a septum

Binary Fission Step 5

A new cell wall and cell membrane is formed

Binary Fission Step 6

Two genetically identical daughter cells are created

Cell Cycle Stages

**Gap 1 G1**:

The new cell starts growing and replicating its organelles

**Synthesis (S):**

DNA replication occurs

**Gap 2 (G2):**

The cell continues to grow in preparation for division

**Mitosis (M) and cytokinesis:**

The single parent cell gives rise to two identical daughter cells.

Gap 0 G0

Performing all cell function but not preparing for cell division

difference of mitosis and cytokinesis

Mitosis is a type of cell division in which a whole cell divides

Cytokinesis is one of the steps of mitosis in which the cytoplasm of the cell divides.

Interphase

•Occurs between divisions

•Longest part of cycle

•‘Normal life’ of cell

•DNA replication happens here

1\. Prophase

Chromosomes appear, nuclear membrane disappears and centrioles form as well as spindles made up from microtubules 

2\. Metaphase

Chromosomes line up across the center of the cell and attach to a spindle fiber 

3\. Anaphase

•Each pair of chromatids are separated at the centromere and moves to the opposite pole 

4\. Telophase

•Nucleus membrane forms

5\. Cytokinesis

•Cytoplasm divides into two

Why is it important for DNA to replicate before cell division?

DNA needs to replicate before cell division in order for new body cells to maintain the same number of chromosomes as their parent cell.

Checkpoints

**End of G1**,

grow or divide? Delay

•Checking DNA for any damage

•Got enough nutrients

•Cell size and growth is normal -> G0

**End of G2**,

* has an error occurred during DNA replication? If yes, then the cell must undergo apoptosis (programmed cell death).
* Check size is normal

**During Mitosis (end of metaphase)**,

are the chromosomes aligned ok? Are the spindle fibres attached correctly? If not, apoptosis will occur.

What happens if the checkpoints don’t work?

uncontrolled and unmonitored cell division, this is commonly known as cancer.

**Apoptosis**

the controlled death of cells in the body also called programmed cell death.

Cell death is required for a number of reasons

•Eg Tadpoles losing its tail and becomes a frog, or a human embryo losing the webbing between fingers and toes.

•Or when cells have reached the end of their life span, ware and tare or infection

•Controlling the number of cells in the body

•Damaged DNA

•Infection

How apoptosis occurs

**•Caspase enzyme is responsible for apoptosis**

•Signalling molecule produced

•Signal transduction occurs

•Stimulates enzymes

•It occurs in a number of steps

Pathways that initiate apoptosis

1\.Mitochondrial Pathway (or intrinsic pathway)

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2\.Death Receptor Pathway (extrinsic pathway)

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1\.Mitochondrial Pathway (or intrinsic pathway)

•Detect damage and release **cytochrome c** into the cytosol which activate caspase enzymes

1\.Death Receptor Pathway (extrinsic pathway)

•Immune cells release death signalling molecules that bind to the receptor proteins on the cell membrane, this initiates the caspase enzymes

Steps of apoptosis

1\.Activation of caspase enzyme

2\.Separation of adjacent cells

3\.Collapse of the cells cytoskeleton

4\.Cell shrinkage

5\.Breakdown of organelles and nucleus

6\.Blebbing of plasma membrane

7\.Membrane breaks apart into vesical that secrete toxins

8\.Phagocytosis of the apoptotic bodies by specialised cells (without spilling cells condense)

***Phagocytosis***

the process by which a cell uses its plasma membrane to engulf a large particle (form of endocytosis)

**Vacuole v.s. Vesical**

•Both are membrane bound organelles

•Vacuole is larger / Vesical is smaller

•Vacuole cannot fuse with the plasma membrane / vesical can

Cell Cell Diagram

Compare and contrast cancer cells with normal cells

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Mutagens

Stem cells

Stem cells are undifferentiated cells which can differentiate into specialised cells

Differentiation

development of a stem cell into a specialized cell with a particular function

Specialised cells

cells which serve a unique particular function (and have a particular structure)

Properties of Stem Cells

**Self-renewal**

Can replicate without disrupting their ability to differentiate (by producing both a differentiated cell and a new stem cell when they replicate)

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**Potency**

Has the capacity to differentiate into different cell types (the higher the potency of a stem cell, the greater the number of cell types it can differentiate into)

Types of stem cells

1\.**Totipotent stem cells**

1\.**Pluripotent stem cells**

1\.**Multipotent stem cells**

1\.**Totipotent stem cells**

•Have the potential to become any cells/a complete new organism

•Occur in embryos (first month of development before the baby becomes a fetus)

•Then change into **blastocyst** which is a ball of cells with hollow outer layer (becomes placenta) with an inner mass (becomes fetus)

2\.**Pluripotent stem cells**

•Can give rise to all types of cells in a fetus (not placenta)

•These are the cells we are investigating for medical use

3\.**Multipotent stem cells**

Give rise to cells that have a particular function \n (e.g. multipotent blood stem cells make white/ red blood cells and platelets)

Compare and Contrast Embryonic vs Adult Stem Cell

Example of differentiated cells

blood cells, skin cells, muscle cells, nerves

induced pluripotent stem cells (IPSCs)

are a type of pluripotent stem cell derived from adult somatic cells that have been genetically reprogrammed to an embryonic stem

(differentiation reversed)

Ethical Concepts

•**Beneficence**

•Is there a benefit to this initiative?

•**Non-maleficence**

•Does it cause harm?

•**Justice**

•Is it fair to everyone? Does it benefit everyone equally? 

•**Respect** 

•Does it show respect/provide dignity to all affected?

•**Integrity**

•Is research doing what it's saying it is going to do? 

Ethics of Stem Cells for Medical Use

Media Response to Article

1\.**Beneficence** Is there a benefit to this initiative?

2\.**Non-maleficence** Does it cause harm?

3\.**Justice** Is it fair to everyone? Does it benefit everyone equally? 

4\.**Respect** Does it show respect/provide dignity to all affected?

5\.**Integrity** Is research doing what it's saying it is going to do?