BCG LO2: Explain the roles of sub-cellular components

Nucleosomes

DNA coiled around histones, condenses during replication to form chromosomes

Chromosomes

Long (q) and short (p) arms

Two identical chromatids bound at centromere

Telomeres - repeat regions which reduce during replication regulate cell life

Nucleolus

Contains dense fibrillar and granular components

Transcribes rRNA

Assembles ribosomal subunits

Involved in pre-rRNA processing

rRNA

Combined with proteins to form ribosomes in the nucleolus

tRNA

Bound to specific amino acids and with complementary anticodon to a specific mRNA codon

mRNA

Carries complementary RNA sequence to DNA coding strand within a gene to ribosome for translation

Nuclear membrane

Continuous w/ ER and contains pores, protects genetic info

Nuclear pores

Protein lined channels usually closed

Opened by nuclear localisation signals

Allow mRNA to be transported to ribosomes

Endoplasmic reticulum

Rough - protein synthesis

Smooth - lipid and carb synthesis (Ca2+ storage in muscles, detoxifying role in liver cells)

Golgi apparatus

Sacs - cisternae

Responsible for PTMs (post-translational modifications - phosphorylation, saccharide or fatty acid addition / cleavage)

Cis → trans movement

Cytosol

70-80% water

Metabolic environment

Mitochondria

Maternally inherited circular DNA - ATP synthase + TCA enzymes, independent replication and protein production

60S ribosomes

Electron transport chain

Complex I - NADH oxidation, 4 protons pumped, ubiquinone reduction

Complex II - FADH2 oxidation, no protons pumped, ubiquinone reduction

Complex III - Ubiquinone oxidation, 4 protons pumped, cytochrome C reduction

Complex IV: Cytochrome C oxidation, 2 protons pumped, oxygen reduction (water formation)

Ribosomes

Protein translation through 40S and 60S subunits

Measure of cell activity and phylogenetic marker due to high conservation

Free - intracellular proteins

Bound - specific proteins (lysosomes, extracellular)

Cytoskeleton

Microfilaments (7nm diameter) - cellular movement dictated by chemokines/cytokines, actin monomers polymerise and hydrolyse

Intermediate filaments (8-10nm diameter) - maintain cell shape and organelle arrangement, structural, filamentous proteins

Microtubules (25nm diameter) - vesicle movement, cell division, extracellular appendages

Centrioles (short microtubule lengths, movement of chromosomes)

Peroxisomes

H2O2 metabolism

Oxidase detoxification

Energy release from fatty acid catabolism

Fission self-replication

Lysosomes

Contain digestive enzymes w/ acidic optimum pH

Active transport proteins pump H+ into vesicle

Highly glycosylated proteins protect membrane from low internal pH

Bud directly from Golgi apparatus

G0

Metabolism halted

Quiescent (dormancy) or senescent (aging/damaged/defective)

G1

Visual inactivity

Organelle duplication and protein production

S phase

Histone and phospholipid production

DNA replication

Cyclin accumulation

G2

Microtubules and other cytokinetic proteins synthesised

Centrosomes polymerise microtubules, for attachment to centromeres

Checkpoint repairs replication errors

Prophase

Breakdown of nuclear membrane

Appearance of spindle fibres

Euchromatin → heterochromatin (chromosomal condensation)

Prometaphase

Spindle fibres attach to condensed chromosomes

Metaphase

Chromosomes align forming along cell equator

Anaphase

Chromosomes divide, chromatids pulled to opposite poles by depolymerising microtubules

Telophase

Nuclear membrane reformation

Heterochromatin → Euchromatin

Spindle fibres disappear