2.4 eukaryotic cell structure

What does microscopy allow you to do?

see what goes on in a healthy cell and observe the changes that take place if the cell is attacked or diseased

what are cells?

basic unit of all living things

What are prokaryotic cells?

single-celled organisms with a simple structure of just a single undivided internal area called the cytoplasm

What are eukaryotic cells?

made up of multicellular organisms like animals, plants and fungi, they have a more complicated internal structure

What is metabolism?

involved both the synthesis (building up) and the breaking down of molecules

What does synthesis mean?

building up

What takes place in the cytoplasm?

reactions

How is the cytoplasm separated from the external environment?

by a cell-surface membrane

Why is the cytoplasm separated into different membrane-bound compartments?

the distinct environments provide conditions for different cellular reactions for the organelles

what are organelles?

a specific structure inside a cell

Are membranes permeable?

yes they control movement of substances in and out of the cell and organelles

what does the nucleus contain?

coded genetic information in the form of DNA molecules

What does DNA do?

directs the synthesis of all proteins required by the cell so it control the metabolic activities of the cell

What is the biggest single organelle in the cell?

the nucleus

Where is DNA contained in the nucleus?

within a double membrane called a nuclear envelope to protect it from damage in the cytoplasm

What does the nuclear envelope contain?

nuclear pores that allow molecules to move in and out of the nucleus

What happens because DNA is too large to leave the nucleus?

it is transcribed into smaller RNA molecules which are exported via the nuclear pores

What protein does DNA associates with?

histones

what complex does histones form?

chromatin

what happens when chromatin coils and condenses?

it forms chromosomes

When are chromosomes visible?

when cells are preparing to divide

What is the nucleolus?

area within the nucleus and is responsible for producing ribosomes

What is the nucleolus composed of?

RNA and proteins

What is RNA used for?

to produce ribosomal RNA (rRNA) which is then combines with proteins to form the ribosomes necessary for protein synthesis

What is the function of mitochondria?

the site of aerobic respiration in cells, their main function is to release energy from glucose (and other fuels) by producing ATP — the cell’s energy molecule.

What depends on the cells number of mitochondria?

the amount of energy it uses so very active cells usually have lots of mitochondria

What type of membrane does mitochondria have?

double membrane

What is the inner membrane of mitochondria?

it is highly folded to form structures called cristae

What is cristae?

highly folded structures on the inner membrane of the mitochondria

What is the fluid interior of the mitchondria?

the matrix

What enzymes are contained in the inner membrane?

enzymes that are used for aerobic respiration

Does mitochondria contain a small amount of DNA?

yes called mitochondrial (mt)DNA

can mitochondria produce their own enzymes and reproduce themselves?

yes

What are vesicles?

membranous sacs that have storage and transport roles

What do vesicles consist of?

a single membrane with fluid inside

What do vesicles transport?

materials inside the cell

What are lysosomes?

specialised forms of vesicles that contain hydrolytic enzymes that break down waste material

how do lysosomes play a role in the immune system?

they break down pathogens which are ingested by phagocytic cells

What is the cytoskeleton?

it is present throughout the cytoplasm of all eukaryotic cells and is a network of fibres necessary for the shape and stability of cells

What does the cytoskeleton control?

the cells movement and the movement of organelles within cells

What is the cytoskeleton made up of?

microfilaments, microtubules and intermediate fibres

What are microfilaments?

contractile fibres formed from actin and is responsible for whole cell movement (phagocytosis), cell contraction (cytokinesis) and gives mechanical strength and support to the cell

What are microtubules?

globular tubulin proteins polymerise to form tubes that form scaffold to provide shape and structure for the cell and act as tracks for organelles to move along, form spindle to move chromosomes in cell division

What is the size of microfilaments?

7nm diameter

what is the size of microtubules

18-30nm diameter

What are intermediate filaments?

made of a variety of proteins and gives mechanical strength to cells and help maintain their integrity 

what is the size of intermediate filaments?

10nm diameter

What are centrioles?

component of the cytoskeleton in most eukaryotic cells that are composed of microtubules and help during cell division by forming spindle fibres that pull chromosomes apart in mitosis and meiosis.

what do two associated centrioles form?

a centrosome which is involved in the assembly and organisation of the spindle fibres during cell division

what is the flagella and cilia?

extensions from the cell membrane

what is flagella?

whip-like and long

what is cilia?

hair-like and short but usually present in greater numbers

what are flagella used for?

cell mobility and sometimes as a sensory organelle which detects chemical changes in the cell’s environment

what are cilia used for?

stationary cilia are a sensory organ to detect changes in the environment and mobile cilia beat in a rhythmic manner to make objects adjacent to the cell move (e.g- moving mucus away from lungs)

What do the cilium contain?

two central microtubules surrounded by 9 pairs of microtubules arranged like a ‘wheel’, known as the 9+2 arrangement

what causes the cilia to move in a beating motion?

pairs of parallel microtubules slide over each other causing it to move

why do cells synthesis proteins?

for internal use and secretion (transport out of the cell)

What is the endoplasmic reticulum (ER)?

network of membranes enclosing flattened sacs called cisternae which is connected to the outer membrane of the nucleus

what is cisternae?

flattened membrane sacs

what is the smooth endoplasmic reticulum (SER)?

responsible for lipid and carbohydrate synthesis and storage

what is the rough endoplasmic reticulum (RER)?

has ribosomes bound to the surface and is responsible for the synthesis and transport of proteins

what cells have more RER?

secretory cells that release hormones or enzymes

where are ribosomes?

free-floating in the cytoplasm or attached to the endoplasmic reticulum forming RER

are ribosomes surrounded by a membrane?

no

what are ribosomes constructed of?

RNA molecules made in the nucleolus of the cell and are the site of protein synthesis

what other organelles contain ribosomes?

mitochondria and chloroplasts (have their own DNA)

what is the structure of the golgi apparatus?

similar to the SER, it is compact structure formed of cisternae and doesnt contain ribosomes

what is the role of the golgi apparatus?

modifies proteins and ‘packaging’ them into vesicles which may be secretory vesicles if the proteins are destined to leave the cell or lysomes which stay in the cell

Where are proteins synthesised?

on the ribosomes bound to the endoplasmic reticulum

protein production:

1. synthesised on the ribosomes bound to the RER

2. pass into the cisternae and packaged into transport vesicles

3. newly synthesised proteins more towards golgi apparatues via transport function of cytoskeleton

4. vesicles fuse with the cis face of golgi and then enter, proteins are structurally modified then leave golgi through the trans face

5. secretory vesicles move towards and fuse with the cell-surface membrane releasing their contents by exocytosis or some form lysosomes used in the cell

how do secretory vesicles release their contents?

exocytosis