Read the information about the nucleus and DNA. Then follow the
directions for drawing below the diagram.
Cell Nucleus - Commanding the Cell
The cell nucleus acts like the brain of the cell. It helps control eating,
movement, and reproduction. If it happens in a cell, chances are the
nucleus knows about it. The nucleus is not always in the center of the cell.
It will be a big dark spot somewhere in the middle of all of the cytoplasm
(cytosol). You probably won't find it near the edge of a cell because that
might be a dangerous place for the nucleus to be. If you don't remember,
the cytoplasm is the fluid that fills cells.
Life Before a Nucleus
Not all cells have a nucleus. Biology breaks cell types into eukaryotic
(those with a defined nucleus) and prokaryotic (those with no defined
nucleus). You may have heard of chromatin and DNA. You don't need a
nucleus to have DNA. If you don't have a defined nucleus, your DNA is
probably floating around the cell in a region called the nucleoid. A defined
nucleus that holds the genetic code is an advanced feature in a cell.
Important Materials in the Envelope
The things that make a eukaryotic cell are
a defined nucleus and other organelles. The
nuclear envelope surrounds the nucleus
and all of its contents. The nuclear
envelope is a membrane similar to the cell
membrane around the whole cell. There
are pores and spaces for RNA and proteins
to pass through while the nuclear envelope keeps all of the chromatin and
nucleolus inside.
When the cell is in a resting state there is
something called chromatin in the nucleus.
Chromatin is made of DNA, RNA, and
nuclear proteins. DNA and RNA are the
nucleic acids inside of the cell. When the
cell is going to divide, the chromatin becomes very compact. It condenses.
When the chromatin comes together, you can see the chromosomes. You
will also find the nucleolus inside of the nucleus. When you look through a
microscope, it looks like a nucleus inside of the nucleus. It is made of RNA
and protein. It does not have much DNA at all.
DNA consists of two long, twisted chains made up of nucleotides. Each nucleotide contains one
base, one phosphate molecule and the sugar molecule deoxyribose. The bases in DNA
nucleotides are adenine, thymine, cytosine and guanine.
Draw, label and color the DNA strand using the same colors you see
here. This will go in your journal – page number is on the board.
Chromosomes and DNA
Chromosomes are DNA wrapped around proteins to
form an X-shaped structure.
The diagram will help you see the relationship.
1. Chromosomes are found in the nucleus
2. Chromosomes are made of DNA
3. Sections of chromosomes are called genes
DNA - deoxyribonucleic acid (it is the genetic code
that contains all the information needed to build and
maintain an organism)
• DNA guides the cell in making new proteins that biological traits.
• DNA gets passed from one generation to the next.
• DNA is one of the nucleic acids, information-containing molecules in the cell.
• DNA is found in the nucleus of almost every cell – prokaryotes usually have
RNA instead of DNA.
Two Types of Cell Division
1. Mitosis- Occurs in body cells (somatic cells) - In mitosis you
start with one cell and end up with two cells that have the same
number of chromosomes as the first cell.
2. Meiosis- Occurs in sex cells (reproductive cells) - In meiosis you
start with one cell and end with four cells that have one-half the
number of chromosomes of the first cell.
Division to Multiply – Mitosis Vocabulary
cell = the basic unit of a living thing
cell division = the dividing of a cell following mitosis
chromosome = the stringlike structure in a cell nucleus that carries information controlling all the cell's activities
DNA = the molecule in each cell that directs the cell's activities
mitosis = the process by which a cell produces two new identical nuclei
The Cell Cycle - Mitosis