Download Cell Division: The Cell Cycle

Cell Division: The Cell Cycle
• Cell Cycle is the pattern of division & growth of a cell.
– It involves the copy & distribution of the genome into 2
daughter cells.
• Genome is a cell’s total hereditary endowment or the entire genetic
code (DNA) found within the nucleus of a cell.
– It takes place inside the somatic cells of humans with the
exception of red blood cells & certain nerve cells.
• Somatic cells are all the body’s cells except the reproductive cells; egg
& sperm.
• Somatic cells contain 46 chromosomes.
– Chromosomes are condensed chromatin into double rods (chromatids) of genetic
material.
» Chromatin
• The mass of very long, thin fibers of DNA & proteins that are found
unwound within the nucleus.
» Chromatid
• ½ of the double-rodded structure of a chromosome
• The cell cycle serves 3 main functions….
1. Reproduction
•
In single-celled organisms, 2 separate individual organisms are
the result of the cell cycle.
2. Growth & development
•
In multi-cellular organisms, rapid copying of cells via the cell
cycle add to the growing organism.
3. Tissue & renewal
•
In multi-cellular organisms that have reached maximum growth,
the cell cycle renews & replaces older cells to maintain and
organism’s size & function.
• The Cell Cycle occurs in 3 stages.
1. Stage 1: Interphase (21 hours)
• Interphase is the longest of the 3 stages of the Cell
Cycle
• Interphase is divided into 3 subphases:
1. G1 (1st gap)
2. S phase
3. G2 (2nd gap)
• The cell begins to grow & enlarge during all 3
subphases of Interphase.
• The cell produces structures that will be used to help
the cell divide into 2 new cells.
– Centromere connects the chromatids or double rods of
chromosomes.
– Centrioles are organelles used to separate & pull
chromosomes into new nuclei.
» Spindle fibers are bands that extend from the centriole & attach to the
chromosome & pull it into separate nuclei.
• The primary process that takes place during Interphase
is the replication of DNA.
– DNA (deoxyribonucleic acid) is the sequence of nitrogen base
pairs that determines the structure of proteins and serves as
the genetic code of life.
– Replication is the process by which the DNA makes an exact
copy of itself.
• DNA (chromatin within the nucleus) replicates or copies
itself only during the S phase of interphase.
• Steps of DNA replication
– Step 1: DNA unzips; bonds connecting nitrogen base pairs
dissolves.
– Step 2: RNA brings in & attaches new nitrogen bases to the
now exposed nitrogen bases resulting in 2 sets of nitrogen
base pairs (Adenine to Thymine & Guanine to Cytosine).
– Step 3: Deoxyribose & Phosphate are brought in to complete
the sides resulting in 2 exact copies of the DNA molecule.
2. Stage 2: Mitosis (<50 minutes)
• During Mitosis, 2 nuclei are created and 1 copy of the
DNA created during Interphase is distributed to each of
the nuclei.
• This process is typically divided into 4 primary phases.
– Phase 1: Prophase
– Phase 2: Metaphase
» Recently a new phase; Prometaphase, has been added in
between Prophase and Metaphase.
– Phase 3: Anaphase
– Phase 4: Telophase
3. Stage 3: Cytokinesis (< 15 minutes)
• The cytoplasm divides.
• The 1st sign of cleavage is the appearance of a cleavage furrow.
– A cleavage furrow is shallow groove in the cell surface near the old metaphase
plate.
• 2 new cell membranes form around the 2 new cells.
• The new cells have an identical set of chromosomes and half of
the organelles.
• Nucleic acids
– Organic molecule that contains the instructions
cells need to carry out all of the functions of life.
– Composed of the elements Carbon, Oxygen,
Hydrogen, Nitrogen & Phosphorus in various
combinations.
– There are 2 types of nucleic acids
• Deoxyribonucleic acid
– More commonly known by the acronym, DNA
• Ribonucleic acid
– More commonly known by the acronym, RNA
• RNA is responsible for carrying the genetic code from
the DNA in the nucleus to Ribosomes.
– Ribosomes are the cell organelle located within the
cytoplasm that is responsible for protein production.
• Proteins are large organic molecules made of carbon, hydrogen,
oxygen, nitrogen & in certain cases, sulfur.
– Amino acids are the building blocks of proteins.
» There are over 20 known amino acids
• 10 essential; must be ingested
• 10 non-essential; the body synthesizes or makes.
• Proteins serve several functions within the body…
– Building blocks for most cell organelles & body structures.
• Hair, skin, fingernails, muscles, etc.
– Proteins form parts of various cells membranes.
– Enzymes are specialized proteins that speed up or slow down
chemical reactions within the body.
• There are 2 types of RNA.
– Type 1: Messenger RNA (mRNA)
• mRNA: responsible for taking a copy of the DNA code from the
chromosomes in the nucleus to the appropriate ribosome.
– Type 2: Transfer RNA (tRNA)
• tRNA: responsible for bring the appropriate amino acid to the ribosome
to build the protein.
• RNA, which stands for ribonucleic acid, contains the
same nitrogen bases as DNA with the exception of one
and is only 1 strand unlike the 2 in DNA.
– Thymine is replaced with Uracil and matches up with Adenine.
• Steps to Protein synthesis
1. Messenger RNA production
•
•
DNA unzips
RNA bases match up along one of the unzipped DNA
strands.
Genetic information is transferred from the DNA strand
to the RNA strand.
•
2. Messenger RNA attaches to a Ribosome
•
The ribosome moves along the messenger RNA strand
reading the genetic code 3 bases (codons) at a time.
–
Codon: a 3 letter combination of the 4 nitrogen bases that
code for & match up to a specific amino acid.
» Stop codons: 3 letter combination that tells the ribosome to
stop adding amino acids to a growing protein chain.
3. Transfer RNA attaches to Messenger RNA
•
•
Based on the specific 3 letter combination (codon) that
is read the transfer RNA retrieves the amino acid that
the codon matches.
The amino acid is then connected to the previous
amino acid.
4. Protein production finishes
•
•
•
The protein chain continues to grow with each amino
acid that is added.
The ribosome reaches a STOP codon or 3 letter
combination that tells the ribosome to stop adding
amino acids to the protein chain.
The protein chain is then released and transported to
the part of the body that it is needed.