The Microstructure of Cells

Question 1

Nucleus main function

Answer 1

Information central of the cell (control and reproduction)

Question 2

How many nuclei are found in cells?

Answer 2

Most have 1, fungi have several, erythrocytes (red blood cells) have none

Question 3

Why do red bloood cells not have nuclei?

Answer 3

Mammalian erythrocytes have nuclei during early
phases of erythropoiesis, but extrude them during development as they mature in order to provide more space for haemoglobin

Question 4

If red blood cells lose their nucleus and other organelles as they mature, why can no virus attack them?

Answer 4

The inability to carry out protein synthesis means that no virus can evolve to target mammalian red blood cells

Question 5

Nuclear envelope

Answer 5

It is a membrane that encloses the nucleus, separating it from the cytoplasm
* This is a double membrane
* Each membrane consists of a lipid bilayer which is continuous with the endoplasmic reticulum
* Pores regulate the entry and exit of molecules from the nucleus

Question 6

How is the shape of the nucleus maintained?

Answer 6

by the nuclear lamina, which is composed of protein – net of protein filaments

Question 7

Where is the nucleolus located? What is its main function?

Answer 7

Within the nucleus and is the site of ribosomal RNA (rRNA) synthesis

Question 8

What are ribosomes?

Answer 8

particles assembled from ribosomal RNA and many different proteins

Question 9

Is it an organelle and what is it amde up of (units)?

Answer 9

No, they are not membrae-bound. Ribosomes are made up of 2 subunits, a large subunit and a small subunit

Question 10

Where are ribosomes found?

Answer 10

-cytosol: free ribosomes (internal proteins)
-rough er/nuclear envelope : bound ribosomes (exported proteins)

Question 11

What is the endomembrane system and what is its function?

Answer 11

Cells that works together to modify, package, and transport lipids and proteins.
Regulates protein traffic and performs metabolic functions in the cell

Question 12

Components of the endomembrane system

Answer 12

• Nuclear envelope
• Endoplasmic reticulum
• Golgi apparatus
• Lysosomes
• Vacuoles
• Plasma membrane

Question 13

Endoplasmic reticulum cell occupation?

Answer 13

accounts for
more than half of the total membrane in many
eukaryotic cells

Question 14

What are the 2 distinct regions of the ER?

Answer 14

• Smooth ER, which lacks ribosomes
• Rough ER, with ribosomes studding its surface

Question 15

Functions of the smooth ER

Answer 15

• Synthesizes lipids
• Metabolizes carbohydrates
• Detoxifies poison
• Stores calcium ions

Question 16

Functions of rough ER

Answer 16

• Has bound ribosomes, which make proteins that are secreted out of the cells
• Many secretory proteins are glycoproteins
  (proteins covalently bonded to carbohydrates)
• The carbohydrate portion is attached to the secretory proteins by enzymes embedded in rough ER
• After synthesis secretory proteins are isolated from the cytoplasm by being wrapped in membranes
• These bud off from the rough ER and move to other parts of the cell
• The membrane buds containing secretory proteins are called transport vesicles
• Is also a membrane factory for the cell

Question 17

Golgi apparatus main function

Answer 17

Shipping and receiving Center

Question 18

What does Golgi apparatus?

Answer 18

Consists of flattened membranous sacs called cisternae

Question 19

Golgi apparatus main function

Answer 19

Shipping and receiving center

Question 20

Golgi apparatus faces

Answer 20

1. The cis face is close to the rough ER and
   is the receiving site for transport vesicles
   * The transport vesicles from the ER fuse with this face and release their content
2. The trans face is the dispatching site where modified and sorted proteins are packaged into new vesicles and released

Question 21

Golgi apparatus functions

Answer 21

• Modifies products of the ER (glycoproteins and phospholipids)
• Manufactures certain macromolecules
• Targets specific products for specific parts of receiving cells by adding molecular identification tags
• Packages secretory products into transport vesicles

Question 22

What is a lysosome?

Answer 22

Membranous sac of hydrolytic enzymes that
can digest macromolecules

Question 23

What do lysosome’s do?

Answer 23

Lysosomal enzymes can hydrolyze proteins, fats,
polysaccharides, and nucleic acids

Question 24

Where are lysosomes made ?

Answer 24

Hydrolytic enzymes and lysosome membrane are made in the rough ER -Golgi

Question 25

What process/es requires lysosomes? Describe the process/es?

Answer 25

Phagocytosis * A lysosome fuses with the food vacuole and digests the molecules * The products of digestion can be used as nutrients by the engulfing cell Autophagy Lysosomes also use enzymes to recycle the cell’s own organelles and macromolecules, a process

Question 26

What are vacuoles ?

Answer 26

Essentially a large vesicle * Contents vary according to cell – or organisms

Question 27

What is the membrane that surrounds vacuoles ?

Answer 27

Tonoplast

Question 28

Types of vacuoles

Answer 28

* Food vacuoles: formed by phagocytosis * Contractile vacuoles: ound in many freshwater protists, pump excess water out of cells * Central vacuoles: found in many mature plant cells, hold ions and organic compounds and water

Question 29

Functions of vacuoles

Answer 29

* In plants = structural roles * Toxic substances may be recycled in the vacuole * Storage for inorganic compounds in plants * Noxious compounds – defense against herbivores stored in vacuoles * Role in plant growth and development (Immature plant cells – small and numerous; mature plants – coalesce to form central vacuole) * Protozoa – specialized = food vacuoles or phagosomes; also contractile vacuoles – pump out water

Question 30

How do mitochondria and chloroplasts change energy from one form to another?

Answer 30

* Mitochondria are the sites of cellular respiration - a metabolic process that generates ATP * Chloroplasts, found in plants and algae, are the sites of photosynthesis

Question 31

Defining characteristics of mitochondria and chloroplasts

Answer 31

* Are not part of the endomembrane system * Have a double membrane * Have proteins made by free ribosomes * Contain their own DNA which codes for some of their proteins and ribosomes

Question 32

Where is mitochondria found and how do we identify it?

Answer 32

* Mitochondria are found in nearly all eukaryotic cells * They have a smooth outer membrane and an inner membrane folded into cristae

Question 33

How do mitochondria convert energy?

Answer 33

* The inner membrane creates two compartments: intermembrane space and mitochondrial matrix * Some metabolic steps of cellular respiration are catalyzed in the mitochondrial matrix * Cristae present a large surface area for enzymes that synthesize ATP

Question 34

What is a chloroplast, what does it contain and where can you find it?

Answer 34

* The chloroplast is a member of a family of organelles called plastids * Chloroplasts contain the green pigment chlorophyll, as well as enzymes and other molecules that function in photosynthesis * Chloroplasts are found in leaves and other green organs of plants and in algae

Question 35

Describe the structure of chloroplast

Answer 35

Thylakoids, membranous sacs, stacked to form a granum The internal fluid is the stroma

Question 36

What are peroxisomes and where are they found?

Answer 36

* Peroxisomes are like specialized lysosomes - metabolic compartments bounded by a single membrane * Peroxisomes are found in organisms including plants , animals (liver & kidney) and protozoa originate from SER)

Question 37

What do peroxisomes do?

Answer 37

* Oxygen is used to break down different types of molecules * Peroxisomes oxidize other molecules and produce hydrogen peroxide which is then broken down - convert it to water

Question 38

What are Glyoxysomes?

Answer 38

* These are specialised peroxisomes * Occur in lipid–storing regions of seeds * When seeds sprout, enzymes of glyoxysomes convert stored lipids to sugars