VCE BIO UNIT 1 AOS1

Extracellular fluid

Fluid present outside of the cells of a multicellular organism.

Intracellular fluid

Fluid present inside of the cell.

Phospholipid Bilayer

Quite fluid, with proteins flowing within it. Glycoproteins, glycolipids, and cholesterol are also apart of membrane structure.

Functions of the plasma membrane

• Maintains internal cell environment.

• Allows movement of substances in and out of the cell.

• Recognition and communication through cells.

Glycoproteins

Have an important role in cellular recognition and immune responses. They help stabilise the membrane structure.

Glycolipids

Act as surface receptors and stabilise the membrane.

Cholesterol

Makes the membrane more stable.

What **can** pass through the plasma membrane? (Hydrophobic or hydrophilic)

Hydrophobic molecules, eg:

• water

• alcohol

• oxygen

What **cannot** pass through the plasma membrane? (Hydrophobic or hydrophilic)

Hydrophilic molecules, eg:

• ions

• large molecules

4 Types of Diffusion

• Simple diffusion

• Facilitated diffusion

• Osmosis

• Active transport

Simple diffusion

The net movement of a substance from a region of high concentration to a region of low concentration.

Movement occurs **down** a concentration gradient, passive process.

Factors affecting rate of diffusion

• Distance

• Concentration gradient

• Physical barriers

• Surface area

Facilitated Diffusion

When a protein channel and/or carrier is used to help pass proteins through the membrane.

Protein Channel

A channel in membrane that some substances need to move through protein instead of passing straight through.

Protein Carrier

A carrier that is supplied in addition to a protein channel, in order to pass through the membrane.

Hypertonic Solution

The solution has a **higher** concentration of solute than the cell or solution that it is being compared to.

Hypotonic Solution

The solution has the **lower** concentration of solute as the cell or solution it is being compared to.

Isotonic Solution

The solution has the **same** concentration of solute as the cell or solution it is being compared to.

Osmosis

The movement of water from a dilute solution to a more concentrated one.

Dilute

A solution with a low concentration of solute, more water molecules than the solute.

Why do cells need osmosis?

It is how they gain water, making them turgid. (swollen, full)

Active Transport

Substances are moved across a membrane __against__ a concentration gradient. It is an active process as it requires energy (ATP). Used to **pump** substances in or out of the cell with specific protein carrier molecules.

What is the cell control system?

A group of proteins that regulate the cell cycle.

How does the cell internally regulate itself?

By using three checkpoints, G1, G2, M.

What happens if the conditions of the checkpoints are not met?

The cell will not enter the next phase of the cell cycle.

G1 Checkpoint (restriction)

End of G1

* Are there adequate resources (nucleotides) for division? Is the cell large enough? Has the DNA been damaged?

G2 Checkpoint

End of G2

* Are there adequate resources (mitotic proteins) for division? Is the cell large enough? Has the DNA been damaged?

M Checkpoint

End of Metaphase

* Have the spindle fibres attached correctly to the chromatids? Are the chromosomes aligned correctly?

External Cell Cycle Controls

• Molecular signals: contact with other cells, tumours release signalling molecules, hormones promote cell division in tissue.

• Environmental conditions: pH levels, temperature, nutrients.

What happens if uncontrolled cell division occurs in a mature organism?

A neoplasm may form.

What is a neoplasm?

An abnormal growth of tissue that can form a mass, for example a tumour. They can eventually become cancer.

What exactly is cancer?

Unregulated and abnormal cell division. It is commonly caused by the increased rate of cell division or the suppression of apoptosis.

Benign Neoplasm

Form localised masses but do not transform into cancer.

Potentially Malignant Neoplasm

Form localised masses that **will eventually** invade other tissues and transform into cancer.

Malignant Neoplasms

Form masses that invade other tissues and transform into cancer.

How are cancer cells different from normal cells?

• Faster division

• Less specialised

• Develop their own blood supply

• DNA mutations occur

• No limited number of divisions

• Can spread to other parts of the body.

What are proto-oncogenes?

They control the stimulation of cell growth and are required for normal growth and development.

Causes of Cancer: Genetic Factors

• Mutations to proto-oncogenes: mutation turns them to oncogenes that promote uncontrolled cell division

• Mutations to tumour suppressor genes

• Hereditary cancers: when someone inherits mutated genes.

Mutagens

Environmental factors that can damage DNA.

Carcinogens

Cancer causing agents.

Causes of Cancer: Environmental Factors

• Chemical: tobacco, air pollution

• Physical: X-Rays, UV light

• Biological: Viruses

Apoptosis

Programmed cell death, highly coordinated process that does not spill cell contents or trigger an immune response.

Why does Apoptosis occur?

• Cells which are damaged or defective must be eliminated.

• During fetal development, the removal of excess cells.

What are Caspases?

Apoptotic Enzymes

What is Phagocytosis?

The breakdown of apoptotic bodies by the phagocytes.

Major Steps of Apoptosis

1. Activation of caspases and begin breakdown of cell contents.

2. Cell shrinks and blebs begin to form.

3. Cells continue to shrink and package themselves into apoptotic bodies.

4. Phagocytosis.

Necrosis

Accidental and uncontrolled cell death, can cause inflammation and damage to surrounding cells.

Why does the cell explode during Necrosis?

The plasma membrane is damaged and ruptures, therefore the cell explodes and contents are released.

What causes Necrosis?

Caused by physical damage, toxins, pathogens, lack of oxygen.

Apoptosis vs Necrosis

• In necrosis, external factors cause internal tissue damage and cell disfunction.

• Apoptosis is pre-planned, and required for smooth bodily functioning..

• Necrosis is cellular death when exposed to extreme conditions.

Apoptotic Pathways

• Mitochondrial Pathway (Intracellular): Triggered when cell components, DNA, is damaged. Proteins signal for beginning of cascade reactions.

• Death Receptor Pathway (Extracellular): Triggered by immune cells outside the target cell. Cells under stress can all trigger this pathway.

Malfunctions in Apoptosis

• Too much apoptosis can lead to degenerative diseases such as Alzheimer’s or Parkinson’s.

• Too little apoptosis is seen in Syndactyly, where the skin between digits is not removed during embryonic development.

How can Apoptosis cause Cancer?

Due to apoptosis not occurring when it should:

• Genetic mutations that increase cell division rate.

• Caspases mutations that prevent function.

• Defects in proteins leading to caspases activation

• Defects in signal reception of apoptosis triggers.

Cascade

Series of caspases reactions.

Why do cells divide? (3 Reasons)

Replace damaged or worn out cells.Allow multicellular animals to grow.Repair damage cells after injury.

How do prokaryotes multiply?

Binary fission

How do eukaryotes multiply?

Mitosis or Meiosis

Binary Fission

Division of prokaryotic cells, asexual production. There are no distinct phases.

Define ‘The Cell Cycle’

The period between the formation of a cell and when it divides.

What are the two phases of the cell cycle?

Interphase and Mitosis

What does IPMATC stand for?

Interphase, Prophase, Metaphase, Anaphase, Telophase, and Cytokinesis.

What is Interphase (G1-S-G2) ?

Cell is undergoing all of its normal activities and doubles in size from the growth of cytoplasm. The chromosomes are not visible as distinct bodies.

Interphase: G1 Stage

G1: growth, organelles are being made and cell specialisation

Interphase: G0

Only occurs if there is a lack of resources or wrong conditions, resting phase.

Interphase: S Phase

The synthesis of DNA, chromosomes are now made of 2 sisters chromatids.

Interphase: G2 Phase

Growth and preparations for division, the synthesis of materials needed for division.

What phase do cells spend most of their time in?

Interphase

What is Mitosis?

The division of eukaryotic cells, one cell divides to form two daughter cells. They all have the same genetic material.

Mitosis: Prophase

Chromosomes condense and become visible, centrioles move to opposite sides and spindle fibres begin to form. Nuclear membrane disappears.

Mitosis: Metaphase

Centromeres of chromosomes attach to spindle and are aligned in the centre of the cell.

Mitosis: Anaphase

Spindle fibres contract, splitting centromere and pull the now separated chromosomes to opposite poles.

Mitosis: Telophase

Nuclear membrane reforms around the two sets of chromosomes as the spindle disappears and chromosomes become longer and thinner.

Mitosis: Cytokinesis

The cells separate and the cell cycle starts again, back to interphase.

Chromosome vs Chromatid

A chromatid is one of the identical halves of a chromosome. It is then replicated and joined with another sister chromatid by the centromere in order to form a chromosome.

What are stem cells?

Cells that have not become specialised yet with the potential to become different types of cells.

The three types of stem cells

• Embryonic stem cells

• Adult (somatic) stem cells

• Induced pluripotent stem cells

The 4 Potencies of Stem Cells

• Totipotent

• Pluripotent

• Multipotent

• Unipotent

Embryonic Stem Cells

Undifferentiated cells from zygote to blastocyst stage.

Totipotent or pluripotent.

Adult Stem Cells

Found in small numbers in adult tissues. Multipotent or unipotent.

Induced Pluripotent Stem Cells (IPSC)

Adult somatic cells that have been genetically reprogrammed to an embryonic cell-like state.

Ethical Dilemmas of Stem Cell Therapies

• Does harvesting embryotic stem cells kill embryos? Taking lives?

• Why use embryos when IPSCs exist?