Question

key ideas
as you read this section, keep these questions in mind:

• what does the cytoskeleton do?
• how does dna direct activity in the cytoplasm?
• which organelles play a role in protein production?
• what is the role of vesicles in cells?
• how do cells get energy?

what gives a cell structure and support?
a cell has a web of protein fibers called a cytoskeleton. the cytoskeleton has three main functions:

• to help the cell move
• to support the cell and help it keep its shape
• to organize the parts of the cell and keep some structures in place

how are activities of the cell directed?
almost all of a cells activities depend on proteins that the cell makes. the instructions for making these proteins are stored in the cells dna. rna carries a copy of the instructions from the dna in the nucleus to the ribosomes in the cytoplasm.
some ribosomes are attached to other organelles. these ribosomes make proteins that will leave the cell.
the nuclear envelope is a double membrane that surrounds the nucleus and separates it from the rest of the cell.
parts of ribosomes are made in the nucleolus.
in a eukaryotic cell, the dna is located in the nucleus.
ribosomes are made up of rna and proteins. some ribosomes are free in the fluid part of the cytoplasm. these ribosomes make proteins that will stay inside the cell.
materials move into and out of the nucleus through nuclear pores.
looking closer

1. compare how does the function of free ribosomes differ from the function of ribosomes attached to other organelles?
2. explain how do materials leave the nucleus?

Explanation:

1. Free ribosomes make proteins that stay inside the cell, while ribosomes attached to other organelles make proteins that will leave the cell. This is based on the location - free ribosomes are in the cytoplasm fluid and attached ribosomes are associated with organelles for export - related protein synthesis.
2. Materials leave the nucleus through nuclear pores. These pores are channels in the nuclear envelope that allow for the passage of molecules such as RNA and proteins.

Answer:

1. Free ribosomes make proteins for internal use in the cell, and ribosomes attached to other organelles make proteins for export from the cell.
2. Materials leave the nucleus through nuclear pores.