Ultrastructure of eukaryotic cells

Question 1

what is the structure of the cytoplasm

Answer 1

• it contains a network of threads and microtubules that help the cell maintain its shape and form.
• it is a thick solution that fills each cell composed of water, salts and proteins.
• includes all of the material in and out of cell. all organelles are located in the cytoplasm. it is highly organised

Question 2

what is the function of the cytoplasm

Answer 2

• transport & structure
• maintains the cells shape
• protects and stores macromolecules
• site of metabolic processes
• contains all organelles

Question 3

what is the structure of the nucleus

Answer 3

• its the largest organelle
• surrounded by a double membrane called the nuclear envelope
• the nuclear envelope has pores containing proteins that control the exit of substances from the nucleus

Question 4

what is the function of the nucleus

Answer 4

• control centre of the cel
• stores the organisms genome
• transmits genetic information
• provides instructions for protein synthesis
• the nuclear envelope separates contents of nucleus from the rest of the cell
• in some regions, the outer and inner nuclear membranes fuse together. some dissolved substances pass through

Question 5

what is the structure of the nucleolus

Answer 5

• doesnt have a membrane around it
• contains RNA
• dark region of chromatin, involved in making chromosomes
• the chromatin is the genetic material consisting of DNA wound around histone proteins. when the cell is not dividing, chromatin is spread out or extended. when the cell is about to divide, chromatin condenses and coils tightly into chromosomes.

Question 6

what is the function of the nucleolus

Answer 6

• where ribosomes are made
• chromosomes contain the organisms genes
• during cell division, chromatin becomes condensed into discrete observable chromosomes
• senses cellular stress. alteration of transfer RNA

Question 7

what is the structure of the mitochondria

Answer 7

• may be spherical, rod shaped or branched about 2-5μm long.
• surrounded by two membranes with a fluid filled space between them.

Question 8

what is the function of the mitochondria

Answer 8

• site of ATP production during aerobic respiration
• self replicating so more can be made if the cell’s energy need increases
• abundant in cells where much metabolic activity takes place
• inner membrane is studded with stalked particles which are the site of ATP synthesis

Question 9

what is the structure of the chloroplast

Answer 9

• large organelles about 4-10μm
• in plant cells and some protoctists
• surrounded by double membrane or envelope
• inner membrane is continuous with membrane sacs (thylakoids) which contain chlorophyll. each stack of thylakoids is a granum

Question 10

what is the function of a chloroplast

Answer 10

• site of photosynthesis.
• 1st stage occurs in the grana - light energy is trapped by chlorophyll and used to make ATP. water is split to supply hydrogen ions.
• 2nd stage occurs in stroma. when hydrogen reduces CO2 using energy from ATP to make carbohydrates

Question 11

what is the structure of a ribosome

Answer 11

• small spherical organelles about 20nm in diameter.
• made of ribosomal RNA
• made in nucleolus as two separate subunits which pass through the nuclear envelope into the cell cytoplasm and then combine
• some remain free in cytoplasm and some attach to the endoplasmic reticulum

Question 12

what is the function of a ribosome

Answer 12

ribosomes bound to the rough endoplasmic reticulum are mainly for synthesising proteins that will be exported outside the cell.
ribosomes that are free in the cytoplasm either singly or in clusters are the site of assembly of proteins that will be used inside the cell

Question 13

what is the structure of the cell membrane

Answer 13

thin flexible layer around the outside of all cells made of phospholipids and proteins

Question 14

what is the function of the cell membrane

Answer 14

seperates content of the cell from the outside environment and controls the entry and exit of materials

Question 15

what is the structure of the cell wall

Answer 15

on the outside of the plasma membrane in plants. made from bundles of cellulose fibres. fungi also have cell walls made of chitin.

Question 16

what is the function of the cell wall

Answer 16

only in plants
prevent plant cells from bursting when turgid.
- provides strength and support
- maintains cell shape
- contribute to strength and support of the whole plant
- permeable, to allow solutions to pass through

Question 17

what is the structure of the smooth endoplasmic reticulum

Answer 17

system of membranes containing fluid filled cavities that are continuous with the nuclear membrane. no ribosomes on its surface

Question 18

what is the function of the smooth endoplasmic reticulum

Answer 18

contains enzymes that catalyse reactions involved with lipid metabolism such as
- synthesis of cholesterol
- synthesis of lipids/phospholipids needed by the cell
- synthesis of steroid hormones
involved with absorption, synthesis and transport of lipids

Question 19

what is the structure of the rough endoplasmic reticulum

Answer 19

similiar to SER but studded with numerous ribosomes giving its rough appearance

Question 20

what is the function of the rough endoplasmic reticulum

Answer 20

The ribosomes synthesise proteins, which are processed in the RER (e.g. by enzymatically modifying the polypeptide chain, or adding carbohydrates), before being exported from the cell via the Golgi Body.

Question 21

what is the structure of the Golgi body or apparatus

Answer 21

consists of a stack of membrane bound flattened sacs. secretory vesicles bring materials to and from the Golgi Apparatus

Question 22

what is the function of the Golgi Apparatus

Answer 22

proteins are modified
- sugar molecules added to glycoproteins
- lipid molecules to lipoproteins
proteins are packaged into vesicles that are pinched of and stored in cell or move to plasma membrane for use or to be exported out of the cell

Question 23

what is the structure of the vacuole

Answer 23

vacuole is surrounded by a membrane called the tonoplast and contains fluid

Question 24

what is the function of the vacuole

Answer 24

only in plants
filled with water and solutes and maintains cell stability. when it is full, it pushes against the cell wall making the cell turgid. if all plant cells are turgid, this helps support the plant

Question 25

what is the structure of the lysosome

Answer 25

small bags formed from the Golgi apparatus. each surrounded by a single membrane. contain powerful digestive enzymes. abundant in phagocytic cells such as neutrophils and macrophages that ingest and digest pathogens.

Question 26

what is the function of the lysosome

Answer 26

keep powerful hydrolytic enzymes separate from the rest of the cell. they engulf old organelles and foreing matter, digest them and return digested compounds to cell for reuse.

Question 27

what is the structure of the cytoskeleton

Answer 27

network of protein structures within the cytoplasm. consists of
- microfilaments = polymers of actin (protein) about 7nm in diameter.
- intermediate filaments about 10nm
- straight cylindrical microtubules of tubulin 18-30nm
cytoskeletal proteins (myosins, kinesins and dyneins) are molecular motors
enzymes and have a site that binds to and allows hydrolysis of ATP as their energy source

Question 28

what is the function of the cytoskeleton

Answer 28

protein microfilaments give support and mechanical strength. keeps cell shape stable and allows cell movement

microtubules help substances and organelles move through cytoplams
- form track which motor proteins drag organelles
- form spindle before cell divides enabling chromosomes to be moved
- make up cilia and undulipodia and centrioles

intermediate filaments anchor the nucleus and extends between cells. stablisise tissues

Question 29

what is the structure of the undilipodium (cillium and flagellum)

Answer 29

protusions from cell and are surrounded by a cell surface membrane
each contain microtubules, formed from centrioles

Question 30

what is the function of the undilipodium (cillium and flagellum)

Answer 30

epithelial cells lining the airways each have many cilia that beat and move mucus. nearly all cell types in the body have one cilium that acts as an antenna. have receptors that allow the cell to detect signals about immediate environment

Question 31

what is the structure of microvilli

Answer 31

These are small finger-like extensions of the
cell membrane found in certain cells such as in the epithelial cells of the intestine and kidney. They are just visible under the light
microscope as a brush border.

Question 32

what is the function of microvilli

Answer 32

they increase the surface area for
absorption of materials.

Question 33

what is the structure of centrioles

Answer 33

consist of two bundles of microtubules (made of tubulin subunits) at right angles to each other. form a cylinder

Question 34

what is the function of centrioles

Answer 34

This is a pair of short microtubules involved in cell division. Before each division the centriole replicates itself and the two centrioles move to opposite ends of the cell, where they initiate the spindle that organises and separates the chromosomes.