the ultrastructure of eukaryotic cells

how to spot the nucleus

big circle in middle of cell

describe the structure of the nucleus

surrounded by a double membrane called the nuclear envelope which is porous

contains chromatin which is the genetic material that contains DNA wrapped around histones. when the cell is not dividing, chromatin is spread out / extended. when it is about to divide, chromatin condenses and wounds tightly to make chromosones. these make up nearly all the organisms genome

describe the function of the nucleus

Contains DNA coiled around chromatin into chromosomes.

Controls cellular processes: gene expression determines specialisation & site of mRNA transcription, mitosis, semiconservative replication.

how to spot the nucleolus

a smaller circle inside a bigger circle

describe the function of the nucleolus

where ribsomes are made

describe the structure of the nucleolus

contains RNA, does not have a membrane

how to spot the nuclear envelope

thicker line around the nucleus

describe the structure of the nuclear envelope

surrounded by a double membrane called the nuclear envelope which is porous

describe the function of the nuclear envelope

to seperate the contents of the nucleus from the rest of the cell (compartmentalisation)

at some points the outer and inner membranes fuse together, here some dissolved substances and ribosomes can pass through

pores enable larger substances like mRNA to leave the nucleus

some substances like steroid hormones may enter the nucleus from the cytoplasm here

how to spot the rough endoplasmic reticulum (RER)

next to nucleus, has ribosomes on it (dots on it - makes it 'rough')

describe the structure of the RER

a system of membranes, containing fluid filled cavities (cisternae) that are continous with the nuclear membrane

coated in ribosomes

describe the function of the RER

The intracellular transport system, the cisternae form channels for transporting substances

provides a large surface area for ribosomes, which assemble amino acids into proteins, these proteins then actively pass through the membrane into the cisternae and are transported to the golgi apparatus for modification and packing

how to spot the smooth endoplasmic reticulum SER

next to RER but no ribosomes, tubular

describe the structure of the SER

a system of membranes containing fluid filled cavities (cisternae) that are continuous with the nuclear membrane

no ribosomes

describe the function of the SER

contains enzymes that catalyse reactions involved with lipid metabolism such as:

• synthesis of cholesterol

-synthesis of lipids/phospholipids

-synthesis of steroid hormones

it is involved with the absorption synthesis and transport of lipids

how to spot the golgi apparatus

fern like shape, vesicles coming off it

describe the structure of the golgi apparatus

Stacks of flattened, membrane-bound sacs. secretory vesicles bring molecules to and from the golgi apparatus

describe the function of the golgi apparatus

proteins are being modified eg

• adding sugar molecules to make glycoproteins

• adding lipid molecules to make lipoproteins

• being folded into their 3d shape

proteins are then packaged off into vesicles that are then pinched off and stored in the cell or moved to the plasma membrane either to be incorporated into it or exported out of the cell

how to spot mitochondria

spherical, rod shaped or branch shaped depending on angle cut at

describe the structure of mitochondria

double membranes with a fluid filled space between them , the inner membrane is highly folded into cristae the inner part of the mitochondrion is a fluid filled matrix

describe the function of the mitochondria

the site of ATP production during aerobic respiration

self replicating and so more can be made of needed

they are abundant in cells where much metabolic activity occurs eg in liver cells or between synapses where a neurotransmitter is synthesised and released

how to spot a chloroplast

large organelle only in plants and some protoctists

describe the structure of chloroplasts

surrounded by a double membrane or envelope, the inner membrane is continous with stacks of flattened membrane sacs called thylakoids (resembling a stack of plates). each stack or pile of thylakoids is called a granum (grana). the fluid-filled matrix is called the stoma.

chloroplasts contain loops of DNA and starch grain

self replicable

describe the function of chloroplats

the site of photosynthesis

the first stage of photosynthesis, when light energy is trapped by chlorophyll and used to make ATP, occurs in the grana. water is also split to supply H ions

the second stage, where H reduces to CO2 using energy from ATP to make carbohydrates, occurs in the stroma. chloroplasts are abundant in leaf cells particularly the palisade mesophyll layer

how to spot a vacuole

big rectangular bit in a plant cell

describe the structure of the vacuole

surrounded by the tonoplast (membrane), contains fluid

describe the function of the vacuole

only plants have it

it is filled with solutes and water to maintain cell stability because when it is full it pushes against the cell wall making the cell turgid

this helps to support the plant (if all cells are turgid)

how to spot lysosomes

little circles

describe the structure of lysosomes

small bags formed by the golgi each is surrounded by a membrane

contain powerful hydrolytic enzmyes

abundant in phagocytic cells

describe the function of lysosomes

compartmenatlise the hydrolytic enzmyes from the rest of the cell

can engulf old organelles and foreign matter to digest them and return digested components for reuse

how to spot cilia and undulipodia

protrusions from the cell

describe the structure of cilia and undulipodia

Protrusions from cell surrounded by surface membrane; contains microtubules; formed from centrioles

describe the function of cilia and undulipodia

The epithelial cells lining your airways each have many hundreds of cilia that beat and move the band of mucus. Nearly all cell types in the body have one cilium that acts as an antenna. It contains receptors and allows the cell to detect signals about its immediate environment. The only type of human cell to have an undulipodium (a longer cilium) is a spermatozoon. The undulipodium enables the spermatozoon to move.

how to spot ribosomes

small circles, some will be on the RER

describe the structure of ribosomes

no membrane

made of ribosomal RNA

made in the nucleolus, as two seperate subunits, which pass through the nuclear membrane into the cell cytoplasm then combine

some remain free in the cytoplasm and some attach to the RER

describe the function of ribosomes

ribosomes bound to the exterior of the RER are mainly for synthesis of proteins to be exported out of the cell

ribosomes are free in the cytoplasm, either singly or in clusters, are primarily the site of proteins that will be used inside the cell

how to spot a centriole

bundles of microtubules at right angles

describe the structure of centrioles

microtubules made of tubulin in a cylinder shape which

two microtubules at a right angle to eachother

no membrane

describe the function of centrioles

before a cell divides, the spindle, made of threads of tubulin, forms from the centrioles

chromosomes attach to middle part of the spindle and motor proteins walk along tubulin threads

they are also involved in the formation of cilia and undulipidia

before the cilia form centrioles multiply and line up beneath the cell membrane

microtubules then sprout outwards from each centriole and form a cilium or undulipodium

usually absent to cells of higher plants but in some unicellular green algae

how to spot cytoskeleton

network of structures

describe the structure of the cytoskeleton

network of protein structures within cytoplasm, consists of: microfilaments, intermediate filaments, microtubules (made of tubulin). cytoskeletal motor proteins walk along structure, and are also enzymes and have a site which binds to and allows hydrolysis of ATP as their energy source

describe the function of the cytoskeleton

protein microfilaments within the cytoplasm give support and mechanical strength, keep the cells stable and allow for cell movement

microtubules also provide shape and support to the cells and help substances and organelles move through the cytoplasm within the cell

• they form the track motor proteins walk along and drag organelles from one part of the cell to another

• form the spindle before the cell divides, which allows chromosomes to be moved along the cell

intermediate filaments are made from a variety of proteins

• anchor nucleus in ctyoplasm

• extend between cells in some tissues, between special junctions enabling cell-to-cell signalling and allow for cells to adhere to a basement structure therefore stabilising tissues

how to spot the cellulose cell wall

thick line around plant cell

describe the structure of the cell wall

The cell wall is a tough, yet flexible layer that surrounds the cell membrane of plant cells made of cellulose fibres

describe the function of the cellulose cell wall

can prevent cells from bursting when turgid

provide strength and support

maintain cells shape

contribute to strength and support of whole plant

permeable to allow solutions to pass through