Cell Biology: Ribosomes and Membranes

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Questions and Answers

What is the primary function of the nuclear envelope?

Control exchange between the nucleus and cytoplasm (correct)

Store genetic material

Facilitate protein synthesis

Provide structural support for the cell

Eukaryotic ribosomes have a higher Svedberg unit compared to prokaryotic ribosomes.

True

What are the two components that make up ribosomes by mass?

Ribosomal RNA (rRNA) and protein

The cell surface membrane is about ___ nm thick.

7 Signup and view all the answers

Match the following cellular structures with their functions.

Nuclear pores = Allow exchange between nucleus and cytoplasm Cell wall = Provides structural support and shape to plant cells Ribosomes = Synthesize proteins Cell membrane = Controls exchange between the cell and its environment Signup and view all the answers

Which type of ribosomes are found in mitochondria and chloroplasts?

70S ribosomes Signup and view all the answers

The cell wall is made of phospholipids and is flexible.

False Signup and view all the answers

What substance is primarily responsible for the rigidity of the plant cell wall?

Cellulose Signup and view all the answers

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

Protein synthesis Signup and view all the answers

The smooth endoplasmic reticulum (SER) is responsible for synthesizing proteins.

False Signup and view all the answers

What structures are formed by the membranes of the endoplasmic reticulum?

Cisternae Signup and view all the answers

The nucleolus is responsible for making __________ using its own DNA.

ribosomes Signup and view all the answers

What happens to the different parts of the nucleolus during nuclear division?

They separate as ribosome synthesis ceases Signup and view all the answers

Match the components of the endoplasmic reticulum with their functions:

Rough ER = Protein synthesis Smooth ER = Lipid and steroid synthesis SER in liver = Drug metabolism SER in muscle cells = Calcium ion storage Signup and view all the answers

Ribosomes are visible with a light microscope.

False Signup and view all the answers

What is the form of RNA used in the manufacture of ribosomes?

rRNA Signup and view all the answers

Study Notes

Ribosomes

Ribosomes are made of two subunits: a large and a small subunit
The size of ribosomes is measured in Svedberg units (S), which indicate the rate at which substances sediment in a centrifuge
Eukaryotic ribosomes are 80S, while prokaryotic ribosomes are 70S
Mitochondria and chloroplasts contain 70S ribosomes, reflecting their prokaryotic origins
Ribosomes are composed of roughly equal amounts of ribosomal RNA (rRNA) and protein
Ribosomes function as the site of protein synthesis, bringing together mRNA, tRNA, amino acids, and regulatory proteins

Cell Surface Membrane

The cell surface membrane is extremely thin, approximately 7 nm
It has three layers: two dark layers surrounding a pale interior
The membrane is selectively permeable, controlling the exchange of substances between the cell and its environment

Nuclear Envelope

The nucleus is surrounded by two membranes forming the nuclear envelope
The outer membrane of the nuclear envelope is continuous with the endoplasmic reticulum
The nuclear envelope contains nuclear pores that regulate the movement of substances between the nucleus and the cytoplasm
Substances leaving the nucleus through pores include mRNA, tRNA, and ribosomes
Substances entering the nucleus through pores include proteins, nucleotides, ATP, and certain hormones

Cell Wall

Plant cells are easily distinguished from animal cells due to their larger size and the presence of a cell wall
The cell wall is an extra structure that lies outside the cell surface membrane
The cell wall is rigid due to the presence of cellulose fibers, providing structural support and shape to the cell

Nucleolus

The nucleolus appears as a darkly stained, rounded structure within the nucleus
Its primary function is to manufacture ribosomes
It contains DNA from one or more chromosomes, containing genes for ribosomal RNA (rRNA) and tRNA
Less dense regions within the nucleolus are where ribosomal subunits are assembled, combining rRNA with proteins from the cytoplasm
Larger cells with higher ribosome production have a larger nucleolus
The nucleolus only exists during ribosome synthesis and disintegrates during nuclear division when synthesis ceases

Endoplasmic Reticulum

The endoplasmic reticulum (ER) is a network of interconnected membranes that form flattened compartments called sacs or cisternae
The ER separates processes occurring within the cisternae from the cytoplasm
The ER facilitates the transport of molecules, primarily proteins, within the cell
The ER is continuous with the outer membrane of the nuclear envelope

Rough Endoplasmic Reticulum (RER)

RER is characterized by the presence of ribosomes attached to its surface
It functions as the site of protein synthesis

Smooth Endoplasmic Reticulum (SER)

SER lacks ribosomes and has a smooth appearance
It is involved in the synthesis of lipids and steroids
SER plays a role in calcium ion storage, crucial for muscle contraction
In the liver, SER participates in drug metabolism

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Description

This quiz covers key concepts related to ribosomes, cell surface membranes, and the nuclear envelope. Explore the structure and function of ribosomes, the selectively permeable nature of cell membranes, and the composition of the nuclear envelope. Test your knowledge on these foundational cell biology topics!