Stage 2 Biology - Cells as a Basis of Life

What is the cell theory?

The cell theory states that all living organisms are composed of cells, cells are the basic unit of structure and function in living organisms, and all cells come from pre-existing cells.

What is the function of the cell membrane?

The cell membrane regulates the passage of substances in and out of the cell, maintaining homeostasis and protecting the cell.

What is the purpose of the double layer of lipids surrounding the cell membrane?

The double layer of lipids, known as the phospholipid bilayer, acts as a barrier to control the movement of substances in and out of the cell.

What is diffusion?

Diffusion is the movement of particles from an area of high concentration to an area of low concentration, resulting in equal distribution.

What is endocytosis?

Endocytosis is a cellular process in which cells absorb molecules by engulfing them with their cell membrane.

exocytosis

Question: What is exocytosis?

Answer: Exocytosis is the process by which cells release substances outside of the cell by fusing vesicles with the cell membrane.

channel proteins

Channel Proteins

Channel proteins are integral membrane proteins that form channels across the cell membrane, allowing the passage of specific ions or molecules. They facilitate the transport of substances such as ions, water, and other solutes across biological membranes. Examples include aquaporins for water transport and ion channels like sodium and potassium channels for ion transport.

What is a key difference between prokaryotic and eukaryotic cells?

Prokaryotic cells lack a nucleus and membrane-bound organelles, while eukaryotic cells have both a nucleus and organelles.

What are autotrophs and heterotrophs?

Autotrophs are organisms that can produce their own food, while heterotrophs rely on other organisms for food.

What is the process by which cells convert glucose into energy using oxygen?

Aerobic respiration.

What is anaerobic respiration?

Anaerobic respiration is the process of producing energy from glucose without the use of oxygen, resulting in the production of lactic acid or ethanol.

What is metabolism?

Metabolism is the process by which your body converts food and drink into energy for essential functions like breathing and digestion.

What are the two main types of metabolic reactions?

Anabolic reactions build molecules, while catabolic reactions break them down for energy.

What is the primary function of ATP energy in a cell?

ATP energy is used as a source of energy for various cellular processes, such as muscle contraction, active transport, and chemical reactions.

Where does cellular respiration occur in eukaryotic cells?

Mitochondria.

What is mitosis?

Mitosis is the process of cell division in which a single cell divides into two identical daughter cells.

What is the process by which a diploid cell divides to produce four haploid cells?

Meiosis

What is a key difference between mitosis and meiosis in terms of chromosome number?

• In mitosis, the daughter cells have the same number of chromosomes as the parent cell,

• while in meiosis, the daughter cells have half the number of chromosomes.

What is interphase?

Interphase is the longest phase of the cell cycle where the cell grows, carries out normal functions, and prepares for cell division.

describe prophase

Prophase is the first stage of mitosis where chromatin condenses into chromosomes, the nuclear envelope breaks down, and the spindle fibers begin to form.

What happens in metaphase during cell division?

In metaphase, chromosomes align at the cell's equator, ready to be separated into two daughter cells during mitosis or meiosis.

what happens in anaphase

In anaphase, sister chromatids separate and move towards opposite poles of the cell, pulled by spindle fibers.

What happens in telophase during cell division?

In telophase, the chromosomes reach the opposite poles of the cell, the nuclear envelope reforms, and the chromosomes begin to decondense.

What is the final stage of cell division?

Cytokinesis, where the cytoplasm divides to form two separate daughter cells.

what is the cell cycle?

an ordered sequence of events that occur in a parent cell for preparation for cell division. Composed of G1, S, G2 and, M phase. Each phase (except S) has its own checkpoint in which cycle is stopped.

The G1 phase (cell cycle)

cell grows in size and carries metabolic reaction like protein synthesis and respiration, accumulates DNA nucleotides and ATP to power DNA replication in S phase.

G1 checkpoint - DNA is checked for availability of DNA nucleotides, ATP, chromosomes checked for mutations and damage.

S phase (cell cycle)

known as the synthesis phase in which chromosomes are replicated and the two copies of chromosomes are joined by a centromere. Centrioles are replicated in prep for mitosis.

G2 phase (cell cycle)

protein synthesis continues, organelles are replicated, ATP synthesis occurs, cell grows in size in preparation for M phase. DNA is checked for damage and is repaired before M phase.

G2 phase - S checkpoint - genome is ensured for whether all chromosomes are replicate and chromosomes are mutation and damage-free.

Mitosis

Cell goes through mitosis

Mitosis phase - sister chromatids are ensured of whether centromere is attached to two spindle fibres before separation in anaphase. Otherwise, one cell will have an extra chromosome lol.

Phosphorylation

the act of adding a phosphate group to another molecule.

Cell cycle signalling molecules

Protein Kinase and Cyclin

protein kinase is an enzyme that activate or deactivate other proteins by phosphorylation. kinases are always in the cell, but are inactive until a cyclin is attached through the lock and key model.

Cyclins are of different concentrations in the cell and a kinase that must be bound to a cyclin is called a cyclin dependent kinase. Cyclin B (mitotic) cyclins are synthesised during S and G2 phases.

Cyclin + CDK = maturation promoting factor (mpf). mpf allows cycle to pass G2 checkpoint. when reached M phase, cyclin are degraded and kinases return to being inactive.

function of MPF in cell cycle

Cyclin B is synthesised and binds to CDK to form a complex called Mitosis Promoting Factor which phosphorylates and activates proteins that facilitate condensation of chromosomes, degradation of nuclear membrane, and assembly of spindle fibres.

why cells carry out aerobic respiration in small regulated steps?

to minimise heat loss and allow gradual production of ATP.

equation for aerobic respiration

C6H12O6 + 6O2 —————→ 6CO2 + H2O + energy

aerobic is the process of releasing energy in the presence of oxygen.

external factor that regulates cell division

growth factors are hormones released by certain cells that stimulate other cells to divide. they bind to receptors proteins on the cell membrane which initiates a metabolic pathway in the cell which synthesises proteins that initiate cell division.

2 applications and limitations to cell culturing

Applications

• scientists culture different cell types to study cell structure and function.

• scientists study interactions between viruses and cultured cells for development of new drugs and vaccines.

Limitations

• contamination by microbes and other cell types is possible in a lab setting.

• cell culture can be costly and time consuming limiting its application in therapeutic use.

why the cell membrane is selectively permeable

The cell membrane is selectively permeable as only certain materials are transported in and out of the cell.

what is simple diffusion?

Simple diffusion is the movement of particles down a region of high concentration to low concentration until the concentration gradient is 0.

what is osmosis?

Osmosis is the passive diffusion of water across a selectively permeable membrane. Water is hydrophilic so its diffusion across the hydrophobic bilayer is too slow to sustain life processes. Hence, water molecules diffuse across aquaporins. Water passively diffuses from a region of low solute concentration to high solute concentration.

define isotonic, hypotonic, and hypertonic and what happens when placing a cell in each type of solution.

Isotonic - solute concentration outside the cell is equal to the solute concentration inside the cell. No change in volume

hypotonic - the solute concentration outside the cell is lower than the solute concentration inside the cell. Cells without a membrane increase in volume and burst.

hypertonic - the solute concentration outside the cell is higher than the solute concentration inside the cell. Cell volume decreases.

facilitated diffusion

Facilitated diffusion is the passive movement of solutes down a concentration gradient and facilitated by integral proteins on the cell membrane.

carrier proteins

carrier proteins selectively bind to substrates in or out of the cell and experience a change in shape to release the substrate to opposite side of the membrane.

effect of environmental factors on enzyme catalysed reactions

when temperatures reach above optimal for an enzyme, the 3d shape of enzyme gets affected, which decreases the rate of enzyme catalysed reactions.

metabolic reactions are slow when competitive or non-competitive inhibitors are present.

alcohol fermentation equation

C6H12O6 ———→ 2c25OH + 2CO2

Lactic acid fermentation equation

C6H12O6 ————> 2C3H6O3

how is the diploid number restored in sexually reproducing organisms.

the diploid number is restored through fertilisation where two haploid gametes combine to form a diploid zygote.