3.2.1.1 Structure of Eukaryotic Cells

Organelle

sub-cellular structure with specific function

Eukaryotic cell

cytoplasm contains membrane-bound organelles
so DNA is enclosed in a nucleus

Function of nucleus

Contains DNA which contains genes which codes for proteins (transcribed into mRNA)
Nucleolus makes ribosomes
Nuclear pores allow substances to move between nucleus and cytoplasm

Structures of a nucleus

Nuclear envelope, nucleolus, nucleoplasm, linear DNA

Nuclear envelope

Double membrane containing nuclear pores

Nuclear pores

Allow the passage of large molecules (mRNA) out of the nucleus.

Nucleoplasm

Granular, jelly like material which takes up the bulk of the nucleus.

DNA

Protein bound (histone), linear DNA in two forms:

• chromatin: condensed

• chromosome: highly condensed

Nucleolus

Small spherical region within the nucleoplasm which is the site of rRNA production and makes ribosomes. (May be more than one)

Types of Endoplasmic reticulum

Rough and smooth

Function of rough endoplasmic reticulum

Site of protein synthesis, transport proteins in RER, transport proteins to Golgi apparatus in vesicles

Function of smooth endoplasmic reticulum

Synthesise and processes lipids (e.g. cholesterol/steriod hormones)

Structure of rough endoplasmic reticulum

Ribosomes, cisternae, large surface area and ability to form shuttle vesicles.

Structure of smooth endoplasmic reticulum

Cisternae, large surface area and ability to form shuttle vesicles.

Cisternae (endoplasmic reticulum)

Corridors that control the transport of polypeptides throughout the cell through compartmentalisation.

Large surface area (endoplasmic reticulum)

Fits a lot of ribosomes for maximised area for polypeptide synthesis

Ability to form shuttle vesicles (endoplasmic reticulum)

Transports polypeptides to Golgi apparatus.

Ribosomes

Site of protein synthesis
Made of 2 subunits (large and small subunit)
Can be found on RER or floating in the cytoplasm.

Function of Golgi Apparatus

Flattened membrane sac that:
Modifies proteins from RER (e.g. protein + carbohydrate → glycoprotein)
Packages proteins into Golgi vesicles
Forms lysosomes.

Structure of Golgi apparatus

Cisternae/membrane bound cavities, enzymes in cisternae, ability to form Golgi vesicles, ability to form lysosomes.

Cisternae/membrane bound cavities (Golgi apparatus)

Compartmentalise the different reactions for the modification of polypeptides into proteins.

Enzymes (Golgi apparatus)

Catalyze the reactions needed for the modification of polypeptides into proteins.

Golgi vesicles

Small membrane-bound sac that transports proteins/lipids to required destination (e.g. cell surface membrane)

Lysosomes

Membrane-bound sac/vesicle that release lysozymes (hydrolytic enzymes)
To hydrolyse pathogens/worn-out organelles

Function of mitochondrion

Site of aerobic respiration to produce ATP for energy release.

Structure of mitochondrion

Cristae, matrix, independent ribosomes/circular DNA, double membrane system.

Cristae

Holds enzymes involved in catalysing the reactions involved in aerobic respiration.
Folded providing larger surface area for reactions.

Matrix

Solution within double membrane of mitochondria containing small ribosomes and circular DNA.

Independent ribosomes/circular DNA in mitrochondria

Manufactures independent proteins within the mitochondria speeding up rate of reaction as the proteins necessary for aerobic reactions made in the mitochondria.

Double membrane system

Compartmentalises substances between membranes (e.g. CO2 of O2)

Why does the mitochondrion look circular in some images?

The mitochondrion have been sectioned at different orientations.

Function of chloroplasts

Absorbs light energy for photosynthesis to produce organic substance e.g. carbohydrates and lipids.

Structure of chloroplasts

double membrane, stroma, thylakoid membrane, grana small ribosomes, circular DNA, starch granules, lipid droplets, lamella

Double membrane in chloroplasts

Compartmentalises the reactions in photosynthesis.

Stroma

Solution within the chloroplast making up the bulk of the cell containing independent ribosomes and DNA, encircling the grana and thylakoids.

Thylakoid membranes/granas

Granas are stacks of thylakoid membranes which provide large surface area to store large amounts of enzymes and chlorophyll needed for photosynthesis.

Independent ribosomes/DNA in the stroma

Manufactures independent proteins within the chloroplast speeding up rate of reaction as the proteins necessary for photosynthesis are made in the chloroplast itself.

Function of starch grains

Store glucose in a cell without affecting cells water potential.

Structure of starch grains

Compact, insoluble, large and easy to hydrolyse.

Compact starch

Maximise amount of carbohydrates stored.

Insoluble starch

Doesn’t affect cells water potential.

Large starch

Cannot diffuse out of the cell.

Easy to hydrolyse starch

Can be quickly used as a source of glucose for respiration.

Lipid droplets

Can be used to make micelles and phospho-lipid bilayer in cell membrane.

Function of Cellulose cell wall

Formed outside the cell surface membrane providing mechanical strength to the cell so prevents osmotic lysis (although is permeable to most substances)

Structure of Cellulose cell wall

Cellulose microfibrils in pectin matrix, permeable, middle lamella, pits and plasmodesmata.

Cellulose microfibrils in pectin matrix

Provides strong composite structure to support plant cell.

Permeable cell wall

Allow passage of important substances into the cell.

Middle lamella

Made of pectin to hold cells together as an adhesive.

Pits and plasmodesmata

Connects cells together.

What are fungal cell walls made out of?

Chitin- a monosaccharide with an amine group

Function of Vacuole

Membrane bound storage area for cell sap (organic and inorganic substances e.g. waste) and maintains turgor pressure.

Structure of Vacuole

Tonoplast, high hydrostatic pressure, coloured pigments, large volume relative to cell.

Tonoplast

Compartmentalises what comes in and out of the vacuole.

High hydrostatic pressure

Pushes chloroplasts to the edge of the cell for easy access to CO2 diffusing into the cell.

Coloured pigments

In some species, for pollution/seed disposal/mating)

Large volume relative to the cell

Maintain turgidity to push chloroplasts

Tissue

Group of specialised cells with similiar structure working together to perform specific function.

Organ

Groups of tissues working together to perform specific functions.

Organ system

Group of organs working together to perform specific functions.

Adaptation of white blood cells/glands

Needs high rate of protein production (antibodies/hormones)
Many ribosomes/RER
For high rate of protein synthesis

Adaptation of muscles cells

High rate of ATP production (due to higher metabolic rate)
So have many mitochondria
For high rate of aerobic respiration/ATP production