2.4 Eukaryotic Cell Structure

Question 1

The NUCLEUS

Answer 1

• contains the genetic code of the cell as DNA molecules, made from the protein Histones to form Chromatin and the Chromosomes
• The DNA is contained within a double membrane within the nucleus known as the NUCLEAR ENVELOPE, allowing for the travel of molecules through NUCLEAR PORES

Question 2

The NUCLEOLUS

Answer 2

• the area within the nucleus that is responsible for producing ribosomes, it is composed of RNA molecules

Question 3

The MITOCHONDRIA

Answer 3

• the sites of cellular respiration and ATP production
• they contain a double membrane, the inner membrane is highly folded into structures called CRISTAE and has a fluid interior called the MATRIX
• have their own DNA (mtDNA) so can reproduce on their own

Question 4

What are VESICLES

Answer 4

• membranous sacs that are simply a single membrane that contains fluid
• they are used to transport materials in, around and out of the cell

Question 5

What are LYSOSOMES

Answer 5

• specialised forms of vesicles that contain hydrochloric enzymes
• they are responsible for the breakdown of waste materials in cells, including old organelles, sometimes the entire cell, in a process known as APOPTOSIS, aka programmed cell death

Question 6

the CYTOSKELETON

Answer 6

a complex of fibres throughout the cytoplasm that uses different types of fibres for different roles:

• Microfilaments: contractile fibres responsible for cell movement and contraction
• Microtubules: globular tubulin proteins which form a scaffold-like structure responsible for cell shape. can also be used as tracks for organelle movement
• Intermediate fibres: these fibres give mechanical strength to the cell and help to maintain its structural integrity

Question 7

What are Centrioles

Answer 7

• a component of the cytoskeleton formed from microtubules
• two together form a centrosome, which is involved in the assembly and organisation of the spindle fibres used in cell division
• thought to be the anchor point of flagella and cilia

Question 8

What are CILIA?

Answer 8

• a hair like extemsion from the cell
• can be stationary or mobile
• stationary cilia have roles in sensory organs ie the nose acting as a filter for dirt
• mobile cilia beat rhythmically moving substances across the cell’s surface found in the trachea
• each cilium contains a central pair of microtubules with 9 pairs around it in a 9+2 arrangement

Question 9

What is a FLAGELLA?

Answer 9

• a whip or tail-like extension from the cell
• used mostly for cell mobility but in some cells are used as sensory organs, detecting chemical changes in the cell’s environment

Question 10

What is the ROUGH ENDOPLASMIC RETICULUM

(RER)?

Answer 10

• a network of flattened membranous sacs called CISTERNAE with ribosomes bound to the plasma membrane
• responsible for the synthesis and transport of proteins

Question 11

What is the SMOOTH ENDOPLASMIC RETICULUM

(SER)?

Answer 11

• a network of flattened membranous sacs called CISTERNAE with ribosomes bound to the plasma membrane
• responsible for the synthesis and storage of lipids and carbohydrates

Question 12

What are RIBOSOMES?

Answer 12

• structures form from rRNA
• site of protein storage
• not membrane bound
• can be free-floating or bound to an organelle’s membrane

Question 13

The GOLGI APPARATUS

Answer 13

• similar in structure to the SER, contains CISTERNAE and no ribosomes
• its role is to modify protiens and package them into vesicles

Question 14

Process of Protein Production

Answer 14

1) RER synthesises proteins
2) they are packaged into vesicles
3) vesicles carry protiens to the Golgi apparatus via the microtubules in the cytoskeleton
4) Golgi apparatus structurally modifies the proteins and packages them into vesicles
5) vesicles either excrete the protiens out of the cell or transport the protiens through the cells