cell nucleus

the nucleus

The nucleus is only found in eukaryotic cells. It contains most of the genetic material (the DNA) of the cell. The genetic material of the nucleus is like a set of instructions. These instructions tell the cell how to build molecules needed for the cell to function properly. That is, the DNA tells the cell how to build molecules needed for life. The nucleus is surrounded by the nuclear envelope, a double membrane (two phospholipid bilayers) that controls what goes in and out of the nucleus. The nucleus also has holes embedded in the nuclear envelope. These holes are known as nuclear pores, and they allow things to flow in and out of the nucleus.


Inside of the nucleus, you will find the chromosomes. Chromosomes are strands of DNA wrapped around proteins. They contain genes, or small units of genetic material (DNA) that contains the code for the creation of a protein. Human cells have 46 chromosomes (23 pairs). There are hundreds to thousands of genes on each chromosome.


The nucleus of many cells also contains a central region called the nucleolus. The job of the nucleolus is to build ribosomes. These ribosomes flow out the nuclear pores into the cytoplasm. Ribosomes are organelles that make proteins in the cytoplasm. See the composition of the nucleus pictured below ( Figure 1.1).


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the nucleus is found in all cells.

a. true

-->  b. false

human cells have 46 genes.

a. true

-->  b. false

which best describes the nuclear envelope?

-->  a) a double membrane that controls what goes in and out of the nucleus.

b) the outside boundary of the nucleus.

c) the nuclear covering that controls whats inside the nucleus.

d) a bilayer that surrounds the nucleus.

which best describes a gene?

a) a unit of dna that is wrapped around proteins.

-->  b) a unit of dna that contains code for the creation of one protein.

c) a unit of dna that gives an individual a trait.

d) an area within the nucleus where ribosomes are made.

which of the following statements is false.

a) ribosomes are the site of protein synthesis.

b) human cells have 46 chromosomes.

-->  c) within the nucleolus is the nucleus.

d) ribosomes are made in the nucleolus.

what is the role of the nuclear pores?

a) nuclear pores determine what enters and leaves a cell.

b) nuclear pores allow ribosomes to be made in the nucleus.

-->  c) nuclear pores allow things to flow in and out of the nucleus.

d) all of the above describe roles of the nuclear pores.

in prokaryotic cells, what is located within the nucleus?

a) the dna

b) the nucleolus

c) the nuclear pores

-->  d) prokaryotic cells do not have a nucleus.

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