Eukaryotic cell structure

Structure of the nucleus

-Surrounded by a nuclear envelope that contain phospholipid bilayer

-300 Nuclear pores allow substances to enter/exit (e.g. mRNA)

-Nucleoplasm contain molecules such as nucleotides and enzymes for DNA and RNA synthesis

-Chromosomes (protein bound, linear DNA)

-Nucleolus makes ribosomal RNA (rRNA) and assembles the ribosomes. (There may be more than one)

Functions of the nucleus

-Contains DNA coiled around chromatin into chromosomes

-Site of mRNA transcription

-Carries genetic information because of DNA

-Manufactures rRNA and assembles ribosomal subunits

Structure of mitochondria

-Double membrane controls the entry and exit of materials

-Cristae are extensions of the inner membrane, they provide a large surface area for the attachment of enzymes and other proteins involved in respiration

-Matrix contains proteins, lipids, ribosomes, respiratory enzymes and DNA that allows the mitochondria to control the production of proteins

-Mitochondrial DNA contain enzymes required for respiration

Functions of mitochondria

-Site of aerobic respiration

-Produces ATP (energy-carrier molecule) from respiratory substrates

-There are lots of large sized mitochondria with a high number of cristae found in cells that has a high level of metabolic activity as they requires a plentiful supply of ATP

Structure of chloroplast

-Vesicular plastid with double membrane controls what enter and leaves

-Grana are stacks of thylakoids, where the first stage of photosynthesis takes place

-Thylakoids contains chlorophyll

-Intergranal lamellae tubes attach thylakoids in adjacent grana

-Stroma is a fluid-filled matrix where the second stage of photosynthesis takes place.They include structures such as starch grains.

Functions and adaptations of chloroplasts

-Granal membrane provides a large surface area for the attachment of chlorophyll, electron carriers and enzymes that carry out the first stage of photosynthesis in a highly ordered fashion.

-The fluid of the stroma possesses all the enzymes needed to make sugars in the second stage of photosynthesis

-Contains DNA and ribosomes so they can quickly and easily make the proteins needed for photosynthesis

Rough endoplasmic reticulum (RER)

-Has ribosomes present on the outer surfaces of the membranes

-Provide a large surface area for the synthesis of proteins and glycoproteins

-Provide a pathway for the transport of materials throughout the cell

Smooth endoplasmic reticulum (SER)

-Tubular appearance

-Synthesise, store, transport lipids and carbohydrates

Role of the golgi apparatus and vesicles

-Consists of cisternae (a stack of membrane that make up flattened sacs) and vesicles

-The proteins and lipids produced by the ER are passed through the golgi apparatus in strict sequence

-Modifies proteins by adding non-protein components, such as carbohydrates

-The golgi sort out proteins and sent to their correct destinations

-Modified proteins and lipids are transported to the golgi vesicles which are pinched off from the golgi cisternae

-Vesicles may move to the cell surface and fuse with the membrane to release substances to the outside

Functions of the golgi apparatus

-Add carbohydrates to the proteins to form glycoproteins

-Produce secretory enzymes

-Secretes carbohydrates

-Transport, modifies, and store lipids

-Form lysosomes

Structure of lysosomes

-Formed when the vesicles in the golgi apparatus contains enzymes (e.g. protease and lipase)

-Contains hydrolytic enzymes which digest unwanted materials

Functions of lysosomes

-Hydrolyse materials injected by phagocytic cells (e.g. white blood cells and bacteria)

-Release enzymes to the outside of the cell in order to destroy materials around the cell

-Digest worn out organelles so the useful chemicals can be re-used

Ribosomes

-Free in cytoplasm or attached to ER

-80s are found in eukaryotic cells, consist of rRNA and proteins

-70s are found in prokaryotic cells, mitochondria and chloroplasts, slightly smaller in size

-Site of protein synthesis via translation

Structure of plant cell walls

-Consists of polysaccharides such as cellulose

-Middle lamella marks the boundary between adjacent cell walls and cements adjacent cells together

Functions of plant cell walls

-Provide mechanical strength to prevent the cell bursting under the pressure created by the osmotic entry of water

-Allow water to pass along and contribute to the movement of water through plants

-Cell walls of algae are made up of cellulose and/or glycoproteins

Vacuoles

-Surrounded by a membrane called tonoplast

-Plant vacuoles cell sap contains a solution of mineral salts, sugars, amino acids, wastes, and pigments

-Support herbaceous plants by making cells turgid

-Sugar and amino acids may act as a temporary food store

-Pigments may colour petals to attract pollinating insects