Animal Cell Organelles

Cell Surface Membrane

• 7nm

• 3 layers - two dark surrounding narrow inside (fluid for endo/exocytosis)

• Phospholipid bilayer and glycoprotein complex

Microvilli

• On cell surface membrane

• Increase SA for absorption

• 1μm

Nucleus (3)

Nuclear Envelope

• Double membrane (outer continuous with endoplasmic retuculum)

• Nuclear pores - gaps in envelope - allow exchange between nucleus and cytoplasm (eg RNA, ribosomes, nucleotides)

Chromosomes and Chromatin

• DNA compact to prevent tangling (chromatin)

• Combines with proteins (histones) to make chromatin

• Chromatin has RNA

Nucleolus

• Darkly stained circle

• Makes ribosomes using own DNA (core of DNA containing genes for rRNA and tRNA)

Endoplasmic Reticulum (2)

• Made of flattened sacs (cristernae)

• Proteins transported through ER separate from cytoplasm

Rough Endoplasmic Reticulum

• Covered in ribosomes for protein synthesis

Smooth Endoplasmic Reticulum

• Makes lipids and steroids (eg cholesterol, testosterone, oestrogen)

• Stores calcium - abundant in muscle cells

Ribosomes

• 2 sub-units - large and smooth - and groove for RNA attachment

• Measured in S (Svedburg) units - measure of centrifugal sedimention speed (70S in prokaryotes, 80S in eukaryotes)

• Made of protein and RNA

• Allows interaction for protein synthesis

Golgi Apparatus

• Stack of flattened sacs (cisternae) constantly being formed at one end from vesicles from ER and broken down at other end to form golgi vesicles

• Stack of cisternae (body) + vesicles = golgi complex/apparatus

• Collects and processes molecules (eg proteins from ER) then transported in vesicles (secretory vesicles)

• Releasing molecules from cell is called secretion done through secretory pathway

• Functions

  • Makes lysosomes

  • Sugars added to proteins (glycoproteins) and lipids (glycolipids)

  • Golgi enzymes help synthesis cell walls (plants)

  • Goblet cells release mucin (in mucus) from golgi complex

Lysosomes

• Single membraned (prevents self absorption) spherical sacs - 0.1 - 0.5μm

• Contains hydrolytic (digestive) enzymes (hydrolases - performs hydrolysis) which breaks down unwanted substances (eg old organelles)

• Performs apoptosis

• Acidic conditions for hydrolysis

• Enzymes synthesised on RER, delivered to lysosomes via golgi

• Autolysis (self absorption) from contents released into cytoplasm

• Endo/exocytosis - movement into cell/out of cell (eg when lysosomal enzymes released for extracellular digestion)

Mitochondria

• 1μm diameter, rod shaped

• Double membrane (intermembrane space), envelope, inner folded into cristae

• Interior = matrix containing nucleoid and ribosomes

• Synthesis of lipids

• Respiration in matrix (contains enzymes in solution) and cristae

• ATP (adenosine triphosphate) broken down to ADP (adenosine diphosphate) for energy in hydrolysis - can be stored and remade into ATP

Microtubules

• Long, hollow, rigid tubes, 25μm diameter

• Acts as cytoskeleton (in cytoplasm) gives cell structure

• Allows movement during nuclear division - spindle fibres

• Made of tubulin (protein α+β)

• Forms centrioles (and also cilia?)

Centrioles

• 9+2 arrangement (9 pairs of microtubules and 2 single ones in the middle)

• At 90˚ to each other outside nucleus in pairs until ready to split

• Hollow cylinder (500nm long)

• Produces cilia

• Cell division - separates chromosomes (mitosis)

Cilia

• Movement of substances (eg in airways)

• 10 μm