structure of eukaryotic cells

eukaryotic cells: structure

• membrane bound organelles

• distinct nucleus

• make up organisms like: animals, plants, fungi, protists, algae

eukaryotic organelles

1. cell surface membrane

2. nucleus

3. mitochondrion

4. chloroplasts

5. golgi apparatus & golgi vesicles

6. lysosome

7. ribosome

8. rough endoplasmic reticulum

9. smooth endoplasmic reticulum

10. cell wall

11. cell vacuole

cell surface membrane

• struc: phospholipid bilayer with embedded proteins, cholesterol, glycolipids and glycoproteins

• func: regulates the movement of substances in and out of cells.

  has receptor molecules on its surface to respond to chemicals like hormones.

membrane: glycolipids and glycoproteins

• glycolipids: carbohydrate chains covalently bonded to a phospholipid

• glycoprotein: carbohydrate chains covalently bonded to an extrinsic protein

• act as cell surface receptors for specific chemicals

• act as antigens: allowing immune system to recognise the body’s own cells vs foreign cells

• help cells attach to one another to form tissues

membrane: cholesterol

• between the tails of the phospholipid bilayer

• restricts lateral movement of phospholipids without making the membrane rigid

• reduces membrane fluidity at higher body temps

• prevents leakage of water and dissolved ions from the cell due to its hydrophobic nature

membrane: phospholipids

• hydrophilic phosphate head and 2 hydrophobic fatty acids tails.

• forms a phospholipid bilayer

• hydrophilic phosphate heads point outward towards the aqueous environment (inside and outside cells)

• hydrophobic tails point inwards, shielded from water

• lipid soluble substances can pass thru = simple diffusion

• water soluble substances cant directly pass thru

membrane: extrinsic (peripheral) proteins

• located on one surface of the bilayer or partially embedded

• often bound to intrinsic proteins or to the hydrophilic phosphate heads

• provides structural support to the membrane

• act as enzymes to catalyse reactions on cell surface

• combine with carbohydrates to form glycoproteins (receptors) for hormones

membrane: intrinsic (integral) proteins

• they span all the way thru the phospholipid bilayers

• the regions of the proteins touching the inner tails are also hydrophobic

• act as transport pathways for water soluble, polar or charged molecules

• facilitated diffusion:

• carrier proteins= bind to large molecules and change shape to carry them across

• channel proteins= create a water-filled pore for specific charged ions

nucleus

• surrounded by a double membrane (nuclear envelope), containing nuclear pores.

• stores DNA in the form of chromosomes

• produces ribosomes

• controls cellular activities by controlling DNA transcription.

nuclear envelope

• a double membrane surrounding the nucleus

• outer membrane = continuous with the RER. And often has ribosomes on its surface.

• controls the entry and exit of materials into and out of the nucleus, and contains the reactions taking place within it

nuclear pores

• small holes in the nuclear envelope = around 40-100nm in diameter)

• allow the passage of large molecules out of the nucleus (eg, mRNA) and ribosomal subunits

• allow substances like proteins and nucleotides into the nucleus

nucleoplasm

• granular, jelly-like material that makes up the bulk of the nucleus (like the cytoplasm)

chromatin/ chromosomes

• made of DNA bound to histone proteins

• when cell is not dividing, DNA exists as diffuse chromatin

• during cell division = chromatin condenses to form visible chromosomes

nucleolus

• small, spherical, dense region within the nucleoplasm

• (there may be more than one in a nucleus)

• synthesises rRNA and assembles ribosomes

mitochondrion

• struc: double membrane, cristae, matrix

• func: site of aerobic respiration, where ATP is produced to provide energy

double membrane

• outer membrane = smooth outer boundary controlling entry and exit of materials

• inner membrane = folded inwards to form extensions called cristae

cristae

• infoldings of the inner membrane

• provide a large SA for the attachment of enzymes and proteins involved in electron transport and ATP synthesis during respiration

matrix

• fluid-filled internal cavity of the mitochondrion

• contains enzymes needed for the Krebs cycle of aerobic respiration

• contains small 70S ribosomes and small, circular DNA (so it can synthesise its own proteins/enzymes)

mitochondrion - key adaptations

• high mitochondrial density = cells with high metabolic activity contain a large number of mitochondria to produce the high amounts of ATP required

• eg: muscle cells, epithelial cells (small intestines)

• dense cristae = highly active cells have mitochondria with more densely packed cristae to further increase the SA for respiration enzymes

chloroplasts

• plant and algal organelles responsible for photosynthesis

• converting light energy into chemical energy

• struc: chloroplast envelope, thylakoids, grana, stroma, internal genetic material

chloroplasts envelope

• double membrane (outer & inner) that controls what enters and exits the organelle

• it is highly selective

thylakoids

• disc-like, membrane-bound structures that contain photosynthetic pigments such as chlorophyll

• where the light-dependent reactions of photosynthesis occur

grana (granum)

• stacks of up to 100 thylakoids

• stacking provides a large SA: for light absorption and for the attachment of photosynthetic pigments, electron carriers and enzymes

• individual grana = joined tgt by thin, flat thylakoid extensions called lamellae

stroma

• fluid-filled matrix surrounding the grana

• contains starch grains and enzymes needed for the light-independent stage of photosynthesis

internal genetic material

• contains 70S ribosomes and short, circular DNA = to quickly synthesise its own proteins and enzymes for photosynthesis

chloroplasts - key adaptations

• large SA: for light absorption and membrane proteins

• fluid stroma: have all necessary enzymes for rapid transport

• self sustaining protein synthesis