Eukaryotes

What is the endosymbiotic theory?

theory that eukaryotic organelles such as mitochondria and chloroplasts from ancient free living prokaryotes invaded primitive eukaryotic cells

What are the several events that preceded the origin of the modern eukaryotic cell in the endosymbiotic theory?

- The origin of a flexible cell surface

- The origin of a cytoskeleton

- The origin of a nuclear envelope, which enclosed a genome organised into chromosomes

- The appearance of digestive vacuoles

- The acquisition of certain organelles via endosymbiosis

Evidence of the endosymbiotic theory

- Structural similarities: both mitochondria & chloroplasts share structural characteristics with free-living bacteria, such as double membranes and DNA

- Reproduction: mitochondria & chloroplasts replicate within the cell independently

- Genetic evidence- DNA within mitochondria & chloroplasts is more similar to bacterial DNA than the host cells nucleus

- Evolutionary relationship- shows that mitochondria & chloroplasts are more closely related to specific groups of bacteria than eukaryotic cells

What is a eukaryote?

Any organism that contains one or more cells that contain DNA in a membrane-bound nucleus.

They contain a large number of specialised membrane-bound organelles

Types of eukaryotes

- Animals

- Protists

- Plants

- Fungi

What are organelles?

True organelles are membrane bound. They are internal membranes suspended in cytoplasm-endomembranes.

Contain compartments for biochemical processes to occur simultaneously and independently

What are the membrane-bound organelles in a eukaryotic cell?

- Endoplasmic reticulum

- Golgi apparatus

- Lysosomes

- Vesicles

- Mitochondria

What are the non-membrane bound organelles in a eukaryotic cell?

- Centrosome/centriole

- Ribosome

These are not membrane bound so technically not organelles

What does the nucleus do?

- Largest organelles

- Controls cell activities by controlling transcription of DNA

- Nuclear membrane contains pores which allow substances in & out

- Easiest organelle to see (under light microscope)

--> stain with hematoxylin & eosin (H & E)

What does the nucleus contain?

- chromatin (made from DNA & proteins)

- nucleolus (makes ribosomes)

What is the endoplasmic reticulum?

Network of flattened cavities (cistern)

--> used in synthesis & processing of proteins & lipids

- Two types of ER: rough & smooth

Rough endoplasmic reticulum

- surface covered with ribosomes that make proteins

- membrane encloses fluid-filled space

- proteins are folded & processed within the rough ER

Smooth endoplasmic reticulum

- similar to rough ER but no ribosomes attached

- lipid synthesis

- lipid processing

What is the Golgi apparatus and what does it do?

- fluid filled, membrane-bound, flattened-sacs

- vesicles often seen at the edges

- process & package new lipids & proteins

- makes lysosomes

What are vesicles and what do they do?

- Packets of membrane

- movement of materials in & out & around cell

What are the three types of vesicles?

- lysosomes

- peroxisomes

- vacuoles

Properties of lysosomes

- membrane bound, made by Golgi apparatus

- round, no clear internal structure

- vesicle contains digestive enzymes

- involved in endocytosis- can digest invading cells or debris enclosed in vesicles

- break-down components that are work out- recylcling

Properties of peroxisomes

- contain enzymes that catalyse some reactions transferring hydrogen to oxygen

--> oxidative reactions

- this detoxifies certain compounds & produces hydrogen peroxide (H2O2)

- peroxisomes contain catalase- enzyme that breaks H2O2 into H2O and O2

Properties of vacuoles

- Smaller than a plant cell vacuole

- Large vesicle

> store water

> store digested food

> store salts

> store pigments

> store metabolic waste

Properties of mitochondrion

- oval shaped, double membrane

- inner membrane folds to form cisternae

- matrix inside

> enzymes for aerobic respiration

> oxidising glucose (Krebs cycle)

- ATP produced

- Numbers vary in cell types:

> more in very active cells with high energy requirements

- contains its own (small) genome of mtDNA

> material inheritance

Properties of ribosomes and what do they do

- Do not have a membrane- technically not an organelle

- Presents in eukaryotes & prokaryotes

- Made of proteins & RNA

- Protein synthesis:

> Translation: RNA to protein (builds primary polypeptide chain)

- Attached to ER or free in cytoplasm

> rough ER ribosomes synthesise proteins for packaging or secretion

> free ribosomes synthesise proteins for cytosol

Properties of centrosome

- Region often near nucleus

- contains centrioles

> ring of microtubules

> nine sets of three microtubules

> centriole pair arranged at right angles

> helps to synthesise microtubules (cytoskeleton)

> helps to organise chromosome during mitosis (cell division)

What does the root of a plant do?

- anchors the plant

- absorbs minerals and water

- stores nutrients

- grows first from embryo

- sometimes specialised

> buttress roots

> aerial roots

> pneumatophores (air roots)

What does the stem of a plant do?

- bears leaves and buds

- chief function is orientation to maximise photosynthesis

- elevate reproductive structures- why?

- limited photosynthesis in green stems

- structure:

> nodes

> internodes

> apical bud (growing tip)

> axillary bud (leaf/branch attachment)

What does the leaf of a plant do?

- main photosynthetic organ

- harvest energy from light

- gaseous exchange

- dissipate heat

- defence

- comprise blade & petiole

What are the three main pigment compounds in a leaf?

- chlorophylls -> green

- carotenes -> orange/red/yellow

- anthocyanins -> pink/red/purple/sometimes blue

What are the two types of vascular tissue in a plant?

- Xylem vessels

- Phloem tissue

Properties of the xylem vessels

- support

-transport water & minerals (upwards)

- long & allow (no cytoplasm)

- no end walls

- form tubes

- walls contain lignin (apart from pits)

> transport in & out

Properties of the phloem tissue

- transport solutes (e.g. sugars from where they are produced to where they are needed & stored)

- no support function

- end walls form seive tubes

> no nucleus

> few organelles

> thin layer of cytoplasm

> can't survive on their own

> needs a companion cell

--> provides energy

--> other 'living' functions

What things do plant cells contain that animal cells don't?

- cell wall

- middle lamella

- plasmodesmata

- pits

- large vacuole

- chloroplasts

- amyloplast

- also different shape to animal cells

Properties of the cell wall

- Rigid structure surrounding plasma membrane

> made of cellulose

- tensile strength & protection

- helps maintain turgor pressure

> prevents wilting by keeping water in and keeping the plant up

- contains plasmodesmata and pits

> areas of cell wall that allow transport & comunication between adjacent cells

What is the middle lamella of the cell wall and what does it do?

- outermost layer

- acts as adhesive

- gives stability

What is the plasmodesmata of the cell wall and what does it do?

- channels in cell wall

- allow transport of substances

- allow communication

What are the pits of the cell wall and what do they do?

- very thin cell wall regions

- arranged in pairs and aligned

- allow transport of substances

Properties of the vacuole of the plant cell

- permanent/central/large vacuole

> 30-90% cell space

> bound by tonoplast membrane

> tonoplast controls what enters & leave vacuole

- filled with sap

> water enzymes, minerals and waste products

- maintains internal pressure

> cell rigidity

- involved in breakdown & isolation of unwanted chemicals in the cell

Properties of chloroplasts

- double membrane

- internal membrane

> thylakoid membrane

> stacked= grand

- lamellae

> link the grana

- site of photosynthesis

> grana & stroma (thick flayed matrix contains DNA, ribosomes, enzymes)

- contains chlorophylls & carotenes

Properties of algal cells

- eukaryotic, uni or multicellular

- carry out photosynthesis

- similar to plants

> cellulose at cell wall

> chloroplast

What are chlamydonas spp?

- A type of algal cell

- single large pyrenoid (posterior end of chloroplast)

> where starch is formed from photosynthetic products

- prominent chloroplast that has a cup or bowl shape

> the chloroplast contains bands composed of a variable number of the photosynthetic thylakoids which are not organised into grans-like structures

- eyespot --> photosensory organelle that perceives light levels & direction