about 2 trillion cells are produced by an adult human body everyday! this is about 2 million new...
TRANSCRIPT
About 2 trillion cells are producedBy an adult human body everyday!
This is about 2 million new cells Every second!!
These new cells are produced When other cells divide.
Cell division is also called Cell reproduction.
Gametes are an organism’s Reproductive cells.
Remember that all of the cellsInformation is stored in the
DNA.
So if/when a cell divides, theDNA must also divide and move
Into the newly created cell.
Bacteria reproduce by a type of Cell division called binary fission.
Binary fission is a form of asexualReproduction that produces
Identical offspring.
In asexual reproduction, a single Parent passes exact copiesOf its DNA to its offspring.
Binary fission occurs in 2 stages…
1st the DNA is copiedAnd 2nd the cell divides.
The bacterium divides by adding A new cell membrane to a pointOn the membrane between the
Two DNA copies.
A new cell wall forms aroundThe new membrane.
Eventually the dividing bacterium isPinched into 2 independent cells.
Each cell contains one of the circlesOf DNA and is a completeFunctioning bacterium.
Eukaryotic cells form chromosomesBefore cell division.
A vast amount of information encodedIn DNA is organized into units
Called genes.
A gene is a segment of DNA that Codes for a protein or RNA molecule.
A single molecule of DNA has Thousands of genes lined up
Like train cars.
Genes play an important role in Determining how a person’s
Body develops and functions.
As a eukaryotic cell prepares to Divide, the DNA and the proteinsAssociated with the DNA coil intoA structure called a chromosome.
Before the DNA coils up, the DNAIs copied.
The two exact copies of DNA thatMake up each chromosome
Are called chromatids.
The two chromatids of a chromosomeAre attached at a point called
A centromere.
Each human cell normally has 2Copies of 23 different chromosomes,
For a total of 46 chromosomes.
The 23 chromosomes differ in size,Shape, and set of genes.
Each of the 23 pairs of chromosomes
Consists of 2 homologous chromosomes,
Also called homologues.
Homologous chromosomes are Chromosomes that are similar in Size, shape, and genetic content.
Each homologue in a pair of Homologous chromosomes comes
From one of the 2 parents.
When a cell contains 2 sets of Chromosomes, it is said to be
Diploid.
Gametes contain only 1 set of Chromosomes.
When a cell contains 1 set ofChromosomes, it is said to be
Haploid.
The haploid number in a humanGamete can be written as
n = 23
The diploid number in a cell can beWritten as 2n = 46
The fusion of 2 haploid gametes,A process called fertilization,A diploid zygote is formed.
A zygote is a fertilized egg cell,The 1st cell of a new individual.
Of the 23 pairs of chromosomes inHuman somatic cells, 22 pairs
Are called autosomes.
Autosomes are chromosomes that are Not directly involved in determining
The sex of an individual.
The sex chromosomes, one of the 23 pairs of chromosomes in humans,Contain genes that will determine
The sex of the individual.
In humans, and other organisms, The 2 sex chromosomes are Referred to as the X and Y
Chromosomes.
The genes that create a male are Located on the Y chromosome and
The genes that create a femaleAre located on the X chromosome.
Cell division in eukaryotic cells isMore complex than bacteria cells.
This is because it involves dividingBoth the cytoplasm and the
Chromosomes.
The life of a eukaryotic cell is Usually shown as a cycle.
The cell cycle is a repeating sequenceOf cellular growth and division.
A cell spends 90% of its time in the First 3 phases-these are collectively
Called interphase.
A cell will enter the last 2 phasesOnly if it is about to divide.
The 5 phases of the cell cycle…
1) First growth phase (G1)
During G1 a cell grows rapidlyAnd carries out its routine functions.
Cells that are not dividing remainIn this phase.
Some cells never divide (muscle & nerve)And thus stay in this phase forever.
2) Synthesis (S) phase.
A cell’s DNA is copied during thisPhase. At the end of this phase,Each chromosome consists of 2
Chromatids attached at the Centromere.
3) Second Growth phase (G2)
In G2, preparations are made for the
Nucleus to divide. Hollow proteinFibers called microtubules are Assembled. The microtubules
Are used to move the chromosomes
During mitosis.
4) Mitosis
The process during the cell divisionIn which the nucleus of the cell is
Divided into 2 nuclei is called Mitosis.
Each nucleus ends up with the same Number and kinds of chromosomes
As the original cell.
5) Cytokinesis
The process during cell division in Which the cytoplasm
Divides is called cytokinesis.
Mitosis and cytokinesis produceNew cells that are identical to
The original cells and allow Organisms to grow.
If a cell spends 90% of its time inInterphase, how do cells know
When to divide?
The cell has checkpoints at whichFeedback signals from the cell
Trigger the next phase of the cycle.
The cell cycle in eukaryotes is Controlled by many proteins, controlOccurs at 3 principle checkpoints…
They are at the end of G1, G2,And at Mitosis.
When cells lose their control overWhen to divide, cancer forms.
During mitosis the nucleus dividesTo form 2 nuclei.
Also, the chromatids on each Chromosome are physically moved
To opposite sides of the dividing cell.
Spindles are cell structures made upOf both centrioles and individual
Microtubule fibers that areInvolved in moving the chromosomes
To opposite sides of the cell.
Mitosis has 4 phases…
Step 1 -> Prophase
Chromosomes coil up and become Visible during prophase. The
nuclearEnvelope dissolves and a spindle
forms.
Step 2 -> Metaphase
During metaphase the chromosomes
Move to the center of the cell and line
Up along the equator. Spindle fibers
Link the chromatids of each Chromosome to opposite poles.
Step 3 -> Anaphase
Centromeres divide during anaphase.The 2 chromatids move towardOpposite poles as the spindle
Fibers begin to shorten.
Step 4 -> Telophase
A nuclear envelope forms around the Chromosomes at each pole.
Chromosomes, now at opposite poles, Uncoil and the spindle dissolves.
Mitosis is complete!
As mitosis ends, cytokinesis begins.
During cytokinesis, the cytoplasmOf the cell is divided in half, and
The cell membrane grows to encloseEach cell, forming 2 daughter cells.
