Biology: Eukaryotic Cell Structure

Question 1

Nucleus

Answer 1

• Largest and densest organelle
• Bounds by a double membrane that has pores (so there is control what enters and leaves this organelle)
  -Contains the DNA which is the code for making proteins. The DNA is associated (wrapped around) proteins called histones.
• DNA replicated happens here
• Transpiration happens here where an mRNA copy is made of a gene.
• The pores allow mRNA to leave and travel to the ribosomes to be used in protein synthesis but they do not allow the larger DNA molecules to leave.

Question 2

Ribosomes

Answer 2

• Smallest, least dense organelle
• Not membrane bound
• Can be found free in the cytoplasm or attached to the surface of the rough E.R.
• Made in the nucleoli of the nucleus
• Site of protein synthesis

Question 3

Nucleolus

Answer 3

• Densely stained region of the necleus
• Ribosomes are constructed here

Question 4

Vesicles

Answer 4

• The sacs fuse with the plasma membrane so that the contents can be secreted to the outside of the cell. This is called Exocytosis.
• The sacs are often formed from the ends of E.R or Golgi apparatus (body)

Question 5

Golgi Apparatus (body)

Answer 5

• Protein, lipids and carbohydrates molecules produced in the ER are modified, and they are transported to the cell surface through the cavities. E.g. carbohydrates can be added to the protein to produce a glycoprotein.
• Form lysosomes

Question 6

Rough ER

Answer 6

• Series of connected, flattened sacs called cisternae spread throughout the cytoplasm of the cell.
• Have ribosomes attached to the surface. The proteins made by the ribosomes are passed into the cytoplasm and are then transported through the cell.
• Vesicles pinch off the cavity and travel to the golgi body where the proteins can be modified (e.g. carbohydrate added to make a glycoprotein), and then secreted.

Question 7

Smooth ER

Answer 7

• Series of connected, more rounded cisternae that do not have ribosomes on the surface.
• Site of lipid sythesis, storage and transport.
• Site of carbohydrates synthesis, storage and transport.

Question 8

Lysosmes

Answer 8

• Vesicles produced by the Golgi that contain enzymes such as proteases and lipases.
• Isolates harmful enzymes from the rest of the cell before releasing them to the outside of the outside of the cell or into a phagocytic vesicle within a phagocyte (white blood cell).
• The enzymes can breakdown the component parts of the cell e.g. digest worn out organelles so that the useful chemicals they contain can be re-used.
• The contents are released when the cell is damaged, dies or is no longer needed (e.g. removing muscle of the uterus after giving birth). The enzymes will break down the cell components to remove the cell. This is called autolysis.
• Phagocytes (white blood cells) have them to breakdown bacterial cells that have been engulfed.
• Release enzymes to the outside of the cell (in a process called exocytosis) to destroy material around the cell.

Question 9

Mitochondria

Answer 9

• Relatively large, rod shaped organelle
• Has a double membrane
• Outer membrane is smooth and controls the movement of molecules in and out of the organelle e.g. prevents respiration enzymes leaving.
• Inner membrane is highly folder to give structures called cristae.
• Inner membrane is highly folder to give structures called cristae.
• On the outside of the cristae are stalked particles.
• The cristae gives a greater surface area over which respiration can take place so that respiration levels can be greater.
• The cristae membrane and stalked particles contain enzymes for producing ATP. The greater surface area they create means that there can be more respiration enzymes and greater ATP production.
• The fluid interior is called the matrix. This contains enzymes for the early stages of respiration, ribosomes for protein synthesis, and DNA for replication of the organelle.
• The site of aerobic respiration
• ATP is made here