Cell Structure and Types (4.5, 4.6, 4.7, and 4.8)

Question 1

Nucleus

Answer 1

The organelle of a eukaryotic cell that contains the genetic material in the form of chromosomes, made of chromatin.
Note —-» The nucleus contains the genetic material encoded in the form of DNA.

Question 2

Note 1 —-»

Answer 2

The DNA is associated with many proteins and organized into structures called chromosomes. The proteins help coil these long DNA molecules. Indeed, the DNA of the 46 chromosomes in one of your cells laid end to end would stretch to a length of more than 2 m, but it must coil up to fit into a nucleus only 5 μm in diameter. When a cell is not dividing, this complex of proteins and DNA, called chromatin, appears as a diffuse mass within the nucleus.

Question 3

Chromatin

Answer 3

The complex of DNA and proteins that make up eukaryotic chromosomes.

Question 4

Note 2 —-»

Answer 4

As a cell prepares to divide, the DNA is copied so that each daughter cell can later receive an identical set of genetic instructions. Just prior to cell division, the thin chromatin fibers coil up further, becoming thick enough to be visible with a light microscope as the familiar separate structures you would probably recognize as chromosomes.

Question 5

Nuclear membrane

Answer 5

A double membrane, that encloses the nucleus, perforated with the pores that regulate traffic with the cytoplasm.
Note —-» Each of the two membranes is a separate phospholipid bilayer with associated proteins.

Question 6

Nucleolus

Answer 6

A structure within the nucleus where ribosomal RNA is made and assembled with proteins imported from the cytoplasms to make ribosomal subunits.

Question 7

Describe the process that occurs in the nucleus.

Answer 7

DNA is copied and passed on to daughter cells in cell division; rRNA is made and ribosomal subunits assembled; protein-making instructions in DNA are transcribed into mRNA.

Question 8

What role do ribosomes play in carrying out the genetic instructions of a cell?

Answer 8

Ribosomes synthesize proteins according to the instructions of messenger RNA, which was transcribed from DNA in the nucleus.

Question 9

Note 3 —-»

Answer 9

Ribosomes may be a cell’s protein-making machines, but running a factory as complex as a cell requires infrastructure and many different departments that perform separate but related functions. Internal membranes, a distinguishing feature of eukaryotic cells, are involved in most of a cell’s functions. Many of the membranes of the eukaryotic cell are part of an endomembrane system. Some of these membranes are physically connected and others are linked when tiny vesicles (sacs made of membrane) transfer membrane segments between them.

Question 10

Endomembrane system

Answer 10

A network of membranes inside and surrounding a eukaryotic cell, related either through direct physical contact or by the transfer of membranous vesicles.

Question 11

Vesicles

Answer 11

A sac made of membrane in the cytoplasm of a eukaryotic cell.

Question 12

Endoplasmic Reticulum (ER)

Answer 12

An extensive membranous network in a eukaryotic cell, continuous with the outer nuclear membrane and composed of ribosome-studded (rough) and ribosome-free (smooth) regions.

Question 13

Which structure includes all others in the list: ER, vesicle, endomembrane system, nuclear envelope?

Answer 13

Endomembrane system

Question 14

Smooth endoplasmic reticulum

Answer 14

That portion of the endoplasmic reticulum that lacks ribosomes.

Question 15

Rough endoplasmic reticulum

Answer 15

That portion of the endoplasmic reticulum with ribosomes attached, that make membrane proteins and secretory proteins.

Question 16

Note 4 —-»

Answer 16

The smooth ER of various cell types functions in a variety of metabolic processes. Enzymes of the smooth ER are important in the synthesis of lipids, including oils, phospholipids, and steroids. Our liver cells also have large amounts of smooth ER, with enzymes that help process drugs, alcohol, and other potentially harmful substances.

Question 17

Glycoprotein

Answer 17

A protein with one or more short chains of sugars attached to it.

Question 18

Transport vesicle

Answer 18

A small membranous sac in a eukaryotic cell’s cytoplasm carrying molecules produced by the cell.

Question 19

Note 5 —-»

Answer 19

The rough ER is a membrane-making machine for the cell. It grows in place by adding membrane proteins and phospholipids to its own membrane. As polypeptides destined to be membrane proteins grow from bound ribosomes, they are inserted into the ER membrane. Phospholipids are made by enzymes of the rough ER and also inserted into the membrane. Thus, the ER membrane grows, and portions of it are transferred to other components of the endomembrane system in the form of transport vesicles.

Question 20

Explain why we say that the endoplasmic reticulum is a biosynthetic workshop.

Answer 20

The ER produces a huge variety of molecules, including phospholipids for cell membranes, steroid hormones, and proteins (synthesized by bound ribosomes) for membranes, other organelles, and secretion by the cell.