Unit 1 Biology - AoS 1

What are living things? (MRS GREEN)

Movement
Reproduction
Sensitivity

Growth
Respiration
Excretion
Equilibrium
Nutrition

Prokaryotes

A group of single-celled organisms with no nucleus and a circular loop of DNA. Bacteria and archaea are both prokaryotic

Eukaryotes

A group of single and multi-celled organisms with a nucleus and linear strands of DNA. Animals, plants, fungi, and protists are eukaryotic

Prokaryote Diversity

There is enormous variation among prokaryotes and they differ both chemically and structurally

Organelle

A cellular structure that performs specific functions

Nucleus

Large organelle surrounded by a nuclear envelope

Comprised of two layers of membrane perforated with nuclear pores - protein-lined channels which allow materials in and out of the nucleus

Contains most of the DNA of the cell - a set of coded instructions for building proteins

Controls and regulates the activities of the cell

Nucleolus

Not technically an organelle

A region of the cells DNA on which ribosomes are made

Ribosomes

Non membrane bounded organelles responsible for protein synthesis

Rough Endoplasmic Reticulum

A membranous chain of connected and flattened sacs which are coated with ribosomes.

This allows it to synthesise and modify proteins.

The rough endoplasmic reticulum typically surrounds, or is close to, the nucleus.

Smooth Endoplasmic Reticulum

A membranous chain of connected and flattened sacs which are not coated with ribosomes.

It is responsible for the production of lipids in a cell.

Mitochondria

An organelle with a highly folded inner membrane surrounded by a second outer membrane.

Mitochondria are the site of aerobic cellular respiration, a chemical reaction that produces the ATP required to power cellular processes.

They also contain their own DNA and ribosomes.

Lysosomes

A membrane-bound vesicle that contains digestive enzymes.

It is responsible for breaking down cell waste and toxins, acting like a garbage disposal.

Golgi Apparatus

Stacked flattened sacs that are the sites of protein sorting, packaging, and modification for use in the cell or export.

Protein-filled vesicles often fuse with or bud off from the Golgi apparatus.

Centrioles

Cell organelle that aids in cell division in animal cells only

Organise the spindle fibres

Chloroplast

A double membrane-bound organelle that contains flattened, fluid-filled sacs that are the site of photosynthesis.

Chloroplasts also contain their own DNA and ribosomes

Vacuole

A membrane-bound sac that is used for water and solute storage.

Vacuoles can also play a role in maintaining plant cell structure.

Plasma Membrane

The plasma membrane is a selectively permeable barrier between the intracellular and the extracellular environment.

It is made of a phospholipid bilayer which is studded with many molecules.

Cell Wall

A sturdy border outside the plasma membrane that provides strength and structure to plant, bacterial, and fungal cells.

Vesicle

A small, membrane-bound sac that transports substances into or out of a cell, or stores substances within a cell.

Cytoskeleton

A large network of protein filaments that start at the nucleus and reach out to the plasma membrane.

The cytoskeleton is critical for maintaining shape and transporting vesicles around the cell.

Aerobic Cellular Respiration

Producing ATP with oxygen by breaking down glucose

C6H12O6 + 6O2 ----> 6CO2 + 6H2O + 36ATP

Photosynthesis

Conversion of light energy from the sun into chemical energy.

6CO2 + 6H2O ---> C6H12O6 + 6O2

Plant VS Animal Cells

Plant cells have a cell wall

Plant cells have chloroplasts

Vacuoles are small in animal cells and large in plant cells

Bioconcave Disc

Shape of red blood cell

Benefits of Small Cells

The exchange of materials with the extracellular environment (including importing nutrients and oxygen, and removing toxins) can occur efficiently and effectively due to a high surface area to volume ratio.

Distances to travel within the cell are smaller, so the intracellular transport of molecules is faster

Cells with High SA:V

Able to exchange substances with the environment most effectively if they have a high SA:V

Example: Small Intestine Cells

Responsible for absorbing nutrients, so they have finger-like shapes called villi which have microvilli

By having villi and microvilli, the surface area to volume ratio is increased, improving function

Function of the plasma membrane

It is the thin boundary of the cell made up of lipids that separates the intracellular and extracellular environments.

It is selectively permeable, which means that only particular molecules can enter and exit the cell.

Thanks to the plasma membrane, cells can have a specialised internal environment.

Phospholipid

The main molecule of which membranes are composed.

Amphipathic due to both hydrophilic and hydrophobic parts - makes membrane stable

Phosphate head

Charged, polar, hydrophilic (attracted to water) part of phospholipids orientated towards the aqueous intra- and extracellular environments

Fatty acid tails

Uncharged, non-polar, hydrophobic (repels and is insoluble in water) parts of phospholipids oriented away from the intra- and extracellular fluid to form the middle portion form the phospholipid bilayer

Integral protein

Proteins that are a permanent part of the membrane

Transmembrane protein

Integral proteins that span the entire bilayer

Peripheral protein

They are proteins which are temporarily attached to the plasma membrane

Functions of Proteins

Transport - channels or pumps that control what enters and exits the cell, making the plasma membrane selectively permeable

Catalysis - speeding up chemical reactions with the help of a protein group called enzymes

Communication - receive signals or recognise cells and molecules. Often attached to the cytoskeleton to transmit signals into the cell

Adhesion - stick to other cells, the extracellular matrix, or the cytoskeleton

What does the fluid mosaic model explain?

The fluid mosaic model explains that 1) molecules that make up the membrane are not held static in one place and 2) many different types of molecules are embedded in the plasma membrane.

Simple Diffusion

Molecules transported:
Non-polar/hydrophobic small molecules eg. oxygen and carbon dioxide

Direction of travel:
Down concentration gradient

No protein required

No energy required

Facilitated diffusion

Molecules transported:
Polar/hydrophilic, large molecules eg. ions, glucose and amino acids

Direction of travel:
Down concentration gradient

Protein required

No energy required

Osmosis

Molecules transported
Water

Direction of travel:
From hypotonic to hypertonic solution

Protein required sometimes (aquaporins)

No energy required

Active transport

Movement of molecules across a semipermeable membrane that requires energy

Protein-mediated active transport

A type of active transport which involves using membrane proteins to move molecules across a membrane against their concentration gradient

Bulk transport

The movement of groups of molecules across the plasma membrane, comes in two forms: exocytosis and endocytosis.

Exocytosis

Release of substances out a cell by the fusion of a vesicle with the membrane.

Endocytosis

Process by which a cell takes material into the cell by infolding of the cell membrane

What is the purpose of cell replication?

Growth and development, maintenance and repair, and reproduction

Binary fission

D - DNA Replication
E - Elongation
S - Septum formation
C - Cell division

Interphase

The first stage of the eukaryotic cell cycle which involves cellular growth and duplication of chromosomes. Composed of three phases: G1, S, and G2

G1 Phase

In the G1 phase, the cell grows by:

• Increasing the volume of its cytosol
• Synthesising proteins for DNA replication
• Replicating its organelles.

At the end of the G1 phase, the cell either proceeds to the S phase or exits the cell cycle and enters the G0 phase.

G0 Phase

Cells that are not required to replicate rest in the G0 phase. Cells in G0 are either quiescent or terminally differentiated. While quiescent cells are dormant and have the ability to re-enter the cell cycle, terminally differentiated cells remain in G0 indefinitely

S (Synthesis phase)

During the S phase, the cell replicates its DNA turning one chromosome into two genetically identical sister chromatids

G2 Phase

The G2 phase is the final stage of interphase where the cell continues to grow and prepare itself for mitosis. The G2 phase is similar to the G1 phase in that it involves:

• Increasing the volume of the cytosol
• Synthesising proteins in preparation for mitosis.

Mitosis

Prophase, metaphase, anaphase, telophase

Prophase

Prophase begins with the condensation of chromatin around histones into distinct chromosomes, so that they become visible under a microscope. Simultaneously, the centrioles migrate towards opposite ends (or poles) of the cell, and spindle fibres begin to form. The nuclear membrane breaks down and the nucleolus disappears.

Metaphase

In metaphase, the spindle fibres fully form and attach to the centromere of each chromosome. This allows the spindle fibres to guide the chromosomes towards the equator of the cell where they line up.

Anaphase

The spindle fibres contract, splitting the centromere and pulling sister chromatids to opposite ends of the cell.

Telophase

The chromosomes densely pack together at either end of the cell, and new nuclear membranes form, producing two genetically identical nuclei. The spindle fibres disintegrate and the chromosomes decondense. Telophase is very similar to the reverse of prophase.

Cytokinesis

After mitosis, cells will undergo cytokinesis. In this stage, the cytoplasm divides and the organelles evenly distribute themselves before separating into two daughter cells.

• In animals, this occurs when a cleavage furrow develops and pinches the plasma membrane into two cells (Figure 7a).

• In plants, because they have a cell wall, a cell plate first forms at the equator before separating into two cells (Figure 7b).

Regulation of the cell cycle

The cell cycle has three checkpoints where the cell inspects itself for errors before proceeding to the next stage. These checkpoints occur at the end of the G1 and G2 phases, and during metaphase. If any errors are detected, the cell can pause for repairs. However, if the damage is irreparable, then the cell undergoes programmed cell death.

G1 Checkpoint

The G1 checkpoint verifies that the cell has grown to the correct size, has synthesised enough protein for DNA replication, checks if the DNA has been damaged during mitosis and cell growth, and checks if there are enough nutrients and oxygen (favourable conditions for mitosis).

G2 Checkpoint

The G2 checkpoint ensures that DNA has replicated properly in the S phase, and that the cell has enough resources for mitosis.

Metaphase Checkpoint

In the metaphase checkpoint, the cell checks the formation of the spindle fibres. If the chromosomes are lined up in the correct location, the cell proceeds to anaphase.

Apoptosis

The controlled death of cells in the body

Mitochondrial pathway

When internal parts of the cell are damaged the mitochondria detects the damage, releases cytochrome C into the cytosol, it binds with cytosolic proteins to form an apoptosome, which activates caspase enzymes, initiating apoptosis

Death receptor pathway

Death signalling molecules can be recognised by death receptor proteins on the surface of cells and are often released by immune cells

When these molecules bind to a death receptor surface protein, caspase enzymes are activated, initiating apoptosis

Stages of apoptosis

1. Activation of caspases - mitochondria release cytochrome C when damage is detected

2. Digestion of cell contents - breakdown of organelles

3. Cell shrinks

4. Membrane blebbing and breakage - membrane warps and detaches from the cell in membrane-enclosed vesicles known as apoptotic bodies

What happens after apoptosis?

After apoptosis, phagocytes engulf and digest the free-floating apoptotic bodies by phagocytosis

What happens when the rate of apoptosis decreases too much?

Cell growth can increase exponentially, resulting in the formation of tumours

Benign tumours

Slow-growing masses of cells enclosed within a capsule, preventing the abnormal cells from separating and invading the rest of the body

Malignant tumours

The cells of some benign tumours can mutate further and become malignant when they gain the ability to invade nearby tissues and/or enter the bloodstream or lymphatic system. From here, they can travel to other parts of the body and grow

Characteristics of tumours

Self-sufficiency

Antigrowth deactivation

Increased survival

Blood supply formation

Tissue invasion and metastasis (unique to malignant tumours)

Stem cells

Stem cells are undifferentiated cells with the capability of differentiating into specialised cells with a particular function.

Properties of stem cells

Self-renewal - stem cells have the capacity to replicate without disrupting their ability to differentiate

Potency - the varying ability of stem cells to differentiate into specialised cell types

Totipotent

Stem cells with the potential to differentiate into any type of cell eg. a zygote

Pluripotent

Stem cells that can differentiate into multiple cell types eg. embryonic stem cells can differentiate into all cell types but placental cells

Multipotent

Stem cells that can differentiate into a limited number of specialised cell types belonging to a specific tissue or organ eg. blood stem cells

Blastocyst

A fluid-filled sphere formed about 5 days after fertilization of an ovum that is made up of an outer ring of cells and inner cell mass. This is the structure that implants in the endometrium of the uterus.

Layers of the blastocyst

Ectoderm, mesoderm, endoderm

Endoderm

Gives rise to the gut and many internal organs

Mesoderm

Gives rise to the muscle cells and connective tissue in the body

Ectoderm

Gives rise to the nervous system and the epidermis, among other tissues