Eukaryotic Cell Structure

Question 1

Structure and function of the nucleus

Answer 1

• made up of nuclear envelope (double membrane), nucleolus
• functions to contain DNA which directs synthesis of all proteins, DNA associates with Histone proteins which form chromatin

Question 2

Nucleolus structure and function

Answer 2

• within the nucleus responsible for producing ribosomes

- it is composed of RNA and proteins

Question 3

Mitochondria structure and function

Answer 3

• have a double membrane, inner membrane highly folded to form cristae which stores enzymes for aerobic respiration
• produces ATP from complex organic molecules which is used for energy

Question 4

Vesicles and lysosomes structure and function

Answer 4

• vesicles are a single membrane sac, used to to transport materials in the cell
• Lysosomes are specialised forms of vesicles, contain hydrolysing enzymes, function to aid digestion and breaking down waste material by fusing with phagocytise cells

Question 5

Cytoskeleton

Answer 5

• microfilaments: formed from protein actin, responsible for cell movement and cytokinesis
• microtubules: determine shape, movement of organelles, and form spindle fibres which segregate chromosomes
• intermediate fibres: strength
• centrioles: component of the cytoskeleton made of microtubules, 2 centrioles form centrosome which is involved in the assembly and organisation of spindle fibres

Question 6

Flagella and cilia structure and function

Answer 6

• flagella and cilia are extensions that protrude from some cell types
• flagella are longer than cilia, but cilia are present in greater numbers
• flagella are used mostly for cell motility however sometimes as a sensory organelle detecting chemical changes in environment
• cilia can be mobile or stationary, stationary cilia eg in the nose play a role in sensory system, mobile cilia function to create a current to cause objects to move
• cilia has a plasma membrane with 2 centre microtubules with 9 pairs of microtubules around the edge of the cell

Question 7

Structure and function of the smooth and rough endoplasmic reticulum

Answer 7

• endoplasmic reticulum is a network of membranes enclosing flattened secs called cisternae, it is connected to the outer membrane of the nucleus
• smooth ER: responsible for the synthesis of lipids and carbohydrates and storage
• rough ER: has ribosomes bound to surface and is responsible for synthesis and transport of protein

Question 8

Structure and function of the ribosomes

Answer 8

• ribosomes can be free floating in the cytoplasm or attached to the rough ER
• they are not surrounded by a membrane, they are constructed of RNA molecules that are made in the nucleolus
• the site of protein synthesis

Question 9

Structure and function of the Golgi Apparatus

Answer 9

• similar in structure to smooth ER, compact structure formed of cisternae, with no ribosomes
• it has a role in modifying proteins and packaging them into vesicles
• either secretory vesicles for use outside the cell or lysosomes for use in the cell

Question 10

Describe the stages of protein production

Answer 10

1) proteins are synthesised in the ribosomes bound to ER
2) they pass into Cisternae and are packaged into vesicles
3) cytoskeleton transports vesicles to Golgi apparatus
4) vesicles fuse with the Cis face of the Golgi and proteins enter, the proteins are structurally modified before leaving the trans face as a vesicle
5) secretory vesicles fuse with the membrane and secrete proteins by exocytosis, or they form lysosomes for use in the cell

Question 11

decribe the differences between eukaryotic cells and prokaryotic cells

Answer 11

prokaryotic cells have no..
- nucleus
-no membrane bound organelles
- no cytoskeleton
prokaryotic cells have smaller (20nm) ribosomes compared to 30nm ribosomes in eukaryotic
- prokaryotic contain pili 
-prokaryotes are much smaller in size

Question 12

definition of membranes

Answer 12

-membranes are partially permeable, therfore control the passage of particular molecules into or out of the cell

Question 13

what is the phospholipid bilayer

Answer 13

• a double layer of phospholipid molecules
• the exterior layer of the bilayer is the hydrophyillic phosphate group that is attracted to water
• the interior layer are the hydrophobic fatty acids

Question 14

name the different components of the plasma membrane

Answer 14

• glycoprotein
• phospholipid bilayer
• intrinsic protein
• glycolipid
• cholesterol
• extrinsic protein

Question 15

what are the functions of membranes within the cell

Answer 15

• create compartments, isolating paticular reactions to prevent the enzymes from being damaged
• carry enzymes, for example in respiration
• carry pigments, eg chlorophyll
• package substances so they can be relased from the cell

Question 16

what are the function of membranes at the surface of the cell

Answer 16

• to control the movement of specific molecules in and out of the cell
• act as receptors for specific hormones or neurotransmitters
• carry electrical signals, eg nerve impulses along neurone
• increase surface area, eg microvilli in the small intestine