Cell structure

Question 1

what is the structure and function of the nucleus?

Answer 1

Surrounded by a double membrane (the nuclear envelope) with nuclear pores. Contains chromatin (DNA wound around histones). Stores the human genome, controls the cell by providing instructions for protein synthesis.

Question 2

what is the structure and function of the nucleolus

Answer 2

it is composed of proteins and RNA and produces ribosomes

Question 3

What is the structure and function of the nuclear envelope?

Answer 3

A double membrane embeded with channel proteins forming pores. Separates the nucleus from the rest of the cell. Pores allow ribosomes and mRNA to leave the nucleus.

Question 4

What is the structure and function of the rough endoplasmic reticulum (RER)?

Answer 4

A system of fluid filled membranes studded with ribosomes. Continuous with the nuclear membrane. Large surface area formed by folding, enables lots of protein synthesis. Proteins pinched off in vesicles transported to the Golgi apparatus.

Question 5

What is the structure and function of the smooth endoplasmic reticulum (SER)?

Answer 5

A system of fluid filled membranes. No ribosomes. Contain enzymes for cholesterol, lipid and phospholipid synthesis.

Question 6

What is the structure and function of the Golgi apparatus?

Answer 6

A stack of flattened membrane bound sacs. Vesicles from the RER join at the cis face. Here they are modified, by adding carbohydrates to make glycoproteins, adding lipids to form glycolipids. Folding proteins into their 3D shape. Modified proteins are pinched off from the trans face into transport vesicles.

Question 7

What is the structure and function of the ribosomes?

Answer 7

2 subunits, large and small. Made of rRNA . Proteins synthesised here.
80s large ribosome found in eukaryotic cells, 70s smaller ribosome found in prokaryotic cells, mitochondria and chloroplast

Question 8

What is the structure and function of the mitochondria?

Answer 8

Double membrane bound. Inner membrane folded into cristae within a fluid filled matrix. Contain own DNA and 70s ribosomes. Site of aerobic respiration, ATP production

Question 9

what is a vesicle?

Answer 9

they are membranous sacs that have storage and transport roles. vesicles are used to transport materials inside the cell

Question 10

what are lysosomes?

Answer 10

are specialised forms of vesicles that contain hydrolytic enzymes. they are responsible for breaking down waste material in the cell, including old organelles. also play important role in immune system as they break down pathogens ingested by phagocytic cells.

Question 11

what do microfilaments do?

Answer 11

they are responsible for cell movement and also cell contraction during cytokinesis. they are formed from the protein actin

Question 12

what do microtubules do?

Answer 12

globular proteins polymerise to form tubes that are used to form a scaffold-like structure that determines the shape of the cell. Also act as tracks for the movement of organelles such as vesicles

Question 13

what do intermediate fibres do?

Answer 13

these fibres give mechanical strength to the cells and help maintain their integrity.

Question 14

what does the cytoskeleton provide?

Answer 14

it provides mechanical strength to cells, helps maintain the shape and stability of a cell. many organelles are help in place by the cytoskeleton.

Question 15

what does the cytoskeleton consist of?

Answer 15

microfilaments, microtubules and intermediate filaments

Question 16

what are centrioles?

Answer 16

made up of microtubules and occurs in pairs to form a centrosome. they are involved in the production of spindle fibres and organisation of chromosomes in cell division

Question 17

what is the structure and function of chloroplasts?

Answer 17

they are surrounded by a double membrane, contains thylakoids (folded membranes embedded with pigment)
fluid filled stroma contains enzymes for photosynthesis
found in plant cells
they are the site of photosynthesis

Question 18

what are cell walls in eukaryotes?

Answer 18

they are found in plant and fungi cells, and they provide structural strength to the cell
in plants- made of microfibrils of cellulose
in fungi - made of chitin, a nitrogen-containing polysaccharide

Question 19

what is the structure and function of the plasma membrane?

Answer 19

they are found in all cells, formed of a phospholipid bilayer, with molecules embedded within and attached on the outside (proteins, carbohydrates, cholesterol)
they control the entrance and exit of molecules

Question 20

how are proteins produced and secreted in the cell?

Answer 20

1- polypeptide chains are synthesis on the RER (ribosomes on the outside)
2- these polypeptide chains move to the cisternae in the RER and are packed into vesicles to be sent to the golgi apparatus via the microtubules
3- in the golgi apparatus, the proteins are modified and packaged into new vesicles
4- the secretory vesicles carry the proteins to the cell surface membrane where it fuses and releases the protein by exocytosis.

Question 21

what are the differences between prokaryotic and eukaryotic cells?

Answer 21

• the cells are much smaller
• no membrane bound organelles
  -smaller ribosomes (70s)
• dna is not contained within a nucleus
• a cell wall made of peptidoglycan
  they may also contain:
• plasmids
• a slime capsule around the cell
• flagella

Question 22

how is dna stored in prokaryotic cells?

Answer 22

they do not have a nucleus so instead they have singular circular dna molecule in the cytoplasm.

plasmids are additional small loops of dna which only carry a few genes