Download cell - Wando High School

Cell Cycle, DNA, and Protein Synthesis
The Cell Cycle
• We have learned that the basic unit of life is the cell.
• Like all living things, the cell goes through a cycle of growth
and reproduction.
• The sequence of growth and division of a cell is called the
Cell Cycle.
• Most of the cell’s life is spent in the growth phase known as
interphase
– made up of three phases:
G1, S, and G2
• The shortest phase in the cycle
is the cell division phase known
as mitosis and cytokinesis.
G1 – GAP 1 – Chromosomes are not visible (chromatin)
Cell is rapidly growing and synthesizing proteins for daily functions
(see diagram on page 228)
The Cell Cycle
Mitosis - Cell divides
the nucleus followed
by cytoplasm division
(cytokinesis) resulting
in two identical
daughter cells
G2 – Gap 2 - Cell is growing and
producing proteins needed for
mitosis
S Stage - Synthesis
Chromosomes are replicated to
form a pair of sister chromatids
connected by a centromere
Mitosis
• During mitosis, one parent cell divides into two
identical daughter cells.
• All somatic cells (cells other than the sex cells
that make eggs and sperm) undergo mitosis.
• There are four phases of mitosis:
–
–
–
–
Prophase
Metaphase
Anaphase
Telophase
Prophase
• This is the first and longest phase in
mitosis.
• The nuclear envelope disappears
• Chromatin coils to become visible
chromosomes
• The two halves of the doubled
structure are called sister chromatids.
• Sister chromatids are exact copies of
each other and are held together by a
centromere.
• In animal cells, the centrioles move to
opposite ends of the cell and start to
form spindle fibers
Metaphase
• The second and shortest phase in
mitosis
• The spindle fibers attach to the
centromere
• The sister chromatids are then
pulled to the middle of the cell
and line up on the midline or
equator
• One sister chromatid from each
pair points to one pole while the
other points to the opposite pole
Anaphase
• The centromeres split and
the sister chromatids are
pulled to opposite poles of
the cell
Telophase
•
•
•
•
Chromosomes uncoil
Spindle is broken down
Nuclear envelope reappears
Cytokinesis begins
Cytokinesis
• Cytoplasm is split forming two
daughter cells each with its own
nucleus and cytoplasmic
organelles
– In animals: a cleavage furrow is
formed that pinches the two cells
apart
– In plants: a cell plate forms between
the two new cells to start the
formation of the cell wall (this does
not occur in animal cells!)
Cell Plate
Name the Phase
Prophase
Metaphase
Prophase
Anaphase
Metaphase
Telophase
Telophase
Anaphase
Controlling the Cell Cycle
• The cell cycle is driven by a chemical control system
telling the cell when to turn on and off cell division
– Internal signals – cell senses the presence of enzymes
produced within the cell
– External signals – cell senses the presence of chemicals (such
as growth factors) produced by other specialized cells
• Cells also respond to physical signals
– When cells are packed in too closely, division
is turned off
– When cells are not in contact with other cells,
division is turned on
Controlling the Cell Cycle
• The cycle control system is regulated at
certain checkpoints
• At each checkpoint, the cell decides if it should go on
with division
– G1 – makes sure conditions are favorable and cell is big
enough for division
– G2 – cell checks for any mistakes in the copies of DNA
– Mitosis – cell makes sure chromosomes and spindle are
arranged properly
• Specific stimuli are required to initiate cell division.
Cell division in most animals cells is in the “off”
position when no stimulus is present
Mitosis Out of Control
• Cancer cells are an example of cells that
do not listen to the cells control system
• Cancer cells keep dividing even though
they may be closely packed together or
no growth factor is present.
• Cancer begins as a single cell
• This cell is normally found and destroyed by the body’s
immune system. If not, this cell could divide into a mass
of identical daughter cancer cells that:
– Impair the function of one or more organs – malignant tumor
• Cells can break off, enter the blood and lymph systems and invade
other parts of the body and become new tumors.
– Remain at their original site – benign tumor
DNA
• Deoxyribonucleic Acid (DNA) contains the
information for life – all the instructions needed to
make proteins (including enzymes)
• A segment of DNA that controls the production of a
protein is called a gene. Hundreds of genes together
make up a chromosome.
DNA  genes  chromosomes
• DNA is a polymer made up of a chain of nucleotides
• Each nucleotide has three parts:
– simple sugar (deoxyribose)
– phosphate group
– Nitrogen base (adenine, guanine, thymine, or cytosine)
DNA Nucleotide Structure
Single ring nitrogen bases
always bind with a double
ring nitrogen base:
DNA Structure
Adenine to Thymine
Cytosine to Guanine
Nucleotide
Nucleotide Sequence
• The DNA of all living things has the same
four nitrogen bases.
• They are different due to the different
sequences of those bases.
– For example, the code ATTGAC would code
for a different protein than TCCAAA
• Because the order of these bases is so
important, DNA must carefully replicate
itself when the cell divides to ensure an
exact copy is passed on to each daughter
cell
DNA Replication
• DNA is un zipped and unwound
by the enzyme helicase
• The enzyme Polymerase
attaches and reads the DNA
• DNA nucleotides find their
compliments on each side of
the DNA strand
• New bases keep attaching until
two identical molecules of
DNA are completed.
• Mitosis would then follow
where each daughter cell would
be given matching copies of
the original DNA
Protein Synthesis
• DNA holds the code for protein synthesis
but it cannot leave the nucleus.
• Protein synthesis is performed at the
ribosomes in the cytoplasm
• The cell uses RNA to copy the code from
DNA and bring it to the ribosomes
• RNA (ribonucleic acid) has three parts:
– Simple sugar (ribose)
– Phosphate group
– Nitrogen base (adenine, cytosine, guanine, and uracil)
• There is no thymine in RNA – it is replaced with uracil
RNA Structure
Transcription
• Copying the portion of DNA
that carries the code for a
protein is called transcription.
• A portion of DNA that codes
for a specific protein is
unwound
• RNA nucleotides find their
compliment
DNA - ATTGCTCCG
RNA - UAACGAGGC
• The RNA strand (mRNA)
releases from the DNA strand
• mRNA strand is edited and
released from the nucleus
Translation
• Translation is the process of
interpreting mRNA to build a
chain of amino acids that
make up a protein
• mRNA leaves the nucleus and
heads to the ribosomes where
translation will occur
• Each sequence of three
nucleotides is called a codon.
• Each codon codes for a
specific amino acid.
UAA CGA GGC
codon codon codon
Translation Steps
• Amino acids are brought to the ribosome
by tRNA
• There are 20 different tRNA molecules,
one for each type of amino acid
• tRNA anticodons find their compliment
codon on the mRNA
mRNA codons – UAA CGA GGC
tRNA anticodons – AUU GCU CCG
• Peptide bonds forms between the amino
acids forming a polypeptide
• Translation stops when a stop codon is
reached
tRNA
Translation Steps (page 308 in your book)
http://www.biostudio.com/dem
o_freeman_protein_synthesis.
htm
Processes and Code Transfer
• Replication – copies DNA to make another
identical double strand of DNA
• Transcription – makes a copy of a section of
DNA and creates a single strand of mRNA
• Translation – reads the sequence of mRNA
nucleotides to build a protein
Mutations
• If the mRNA
does not copy
the code
correctly, the
amino acid chain
will be altered –
this is called a
mutation