Cell Cycle

Cell Cycle

Basics of the Cell Cycle

The cell cycle is the process of making new cells. It is composed of multiple phases and occurs within milliseconds. The cell cycle is vital to the creation of cells to help with the body’s functions and keep it alive.

The cell cycle is composed of the following phases:

• Interphase (G1 phase: the cell contents are duplicated, S phase: the DNA is replicated, G2 phase: the parts of the cell that have been copied till now are rechecked)
• Prophase
• Metaphase
• Anaphase
• Telophase
• Cytokinesis

* Prophase, Metaphase, Anaphase, and Telophase are a part of mitosis

The Beginning Phase

Interphase

• All of the cell functions are normal
• The cell grows in size and carries on to metabolism
• The chromosomes of the cell are duplicated
• Cells will spend the majority of their time in interphase

Mitosis

Mitosis Characteristics

• Mitosis is the division of somatic (body) cells
• The result of mitosis is two daughter cells

Prophase

• This is the longest of all the phases in mitosis
• The chromosomes become visible
• The nuclear membrane disintegrates
• In animal cells, spindles start to form from the centrioles
• In plant cells, spindles form on their own\

Metaphase

• The chromosomes start to line up in the cell
• Centromeres attach to the spindles
• They make sure that each cell gets an exact copy

Anaphase

• The chromosomes that are separated by the spindle fibers start to move and shorten

Telophase

• This phase begins when the chromosomes reach opposite sides of the cell
• A new nuclear cell membrane starts to form around the chromosome
• The cells begin to prepare for separate existence\

After Mitosis

Cytokinesis

• Cytoplasm division occurs
• The animal’s cells end up forming a “cleavage furrow”
• The plant’s cells end up forming a “cell plate”

End of cycle

• Two genetically identical daughter cells are formed
• The cells are diploid, meaning they contain both pairs of chromosomes

DNA Replication

DNA Characteristics

• DNA- stands for deoxyribose nucleic acid
• Deoxyribose sugar- deoxyribose is the sugar used to create DNA
• Nucleic acid- DNA is a form of nucleic acid
• Double helix- this is when there are two strands that are twisted together in a cell

How to make a nucleic acid monomer

• The monomer- Nucleotide

• Deoxyribose sugar
• Phosphate (p)
• Nitrogen Base

• Adenine
• Thymine
• Cytosine
• Guanine

• The phosphate, deoxyribose sugar, and nitrogen base all connect to each other and form a monomer. Those monomers connect to each other and that’s how the DNA strands are formed.

Complementary base pairs

Guanine pairs with Cytosine and Adenine pairs with Thymine.

There should be the same number of cytosine as there is guanine and the same number of adenine as there is thymine.

For example: 12C=12G and 5A=5T

Antiparallel

• DNA is considered antiparallel
• DNA has a 5’ to 3’ side and a 3’ to 5’ side (read the apostrophe as “prime”)
• The top strand is 3’ to 5’
• The bottom strand is 5’ to 3’

DNA Replication Process

• DNA replication helps with the creation of new cells
• The replication of DNA should result in an exact copy of itself
• DNA strands are semiconservative, meaning that DNA is a double helix. Because of this, at the end of the process, the DNA helix will end up with one original strand and one new strand.
• The replication enzymes in DNA replication are:

• Helicase- unzipper (unwinds DNA helix)
• DNA polymerase- copier (copies DNA strands)
• Primase- initializer (guides polymerase)
• Ligase- glue (Fixes gaps in lagging strand)

Steps for DNA Replication

1. The DNA unwinds with helicase
2. The primase tells the polymerase where to go
3. Polymerase is making a new strand for DNA helix. Polymerase only moves in the 3’ to 5’ direction.
4. The movement of the polymerase causes gaps on the lagging strand (the 5’ to 3’ strand). The primase needs to back up and tell the polymerase to back up so the strand is copied correctly.
5. The primase and polymerase movement causes gaps in the lagging strand. Those fragments are called Okazaki fragments and are filled in ligase enzymes.
6. The final DNA has old and one new strand.