Chapter 8: DNA replication, binary fission, mitosis

A gene is

segment of DNA which codes for a protein

Heredity

A gene contains instructions for building RNA and proteins

Not all genes are expressed in every cell

Genome

All the genetic information in an organism; all of an organism's chromosomes.

All cells divide

No living organisms can reproduce without cell division

unicellular organisms divide in order to reproduce

Cell division produces a continuous supply of replacement cells in multicellular organisms

Cell division

One cell divides into two cells

Cell theory:

All cells come from other cells

Eukaryotic cells divide by mitosis:

A fertilized egg or zygote divides by mitosis

The fetus grows and develops into a mature adult consisting of countless cells.

Eukaryotic cells divide by meiosis:

Each mature individual produces sex cells by another fork of cell division called meiosis

Meiosis occurs only during reproduction

Gametes fuse during fertilization

Sex cells produce by meiosis contain half the DNA as body cells

At fertilization, the zygote inherits DNA from both gametes

Cells divide as theyre needed (cell division)

Mitotic cell divisions allow an organism to:
Grow and develop
Repair tissues
Regenerate lost body parts
Reproduce asexually by mitosis

Apoptosis

process of programmed cell death as needed (duck feet)

DNA replication precedes cell devision

Cells must copy their DNA before they can divide

The entire genome is replicated so that each new cell gets one complete copy of DNA

Genome

Complete DNA sequence for a particular organism or individual

In DNA replication both strands are copied

DNA is made of two chains of nucleotides called strands. They are complementary to each other because of how the nitrogenous bases match up.
A-T
G-C
Each strand acts as a template- they are both used to build a new molecule of DNA

DNA replication is semiconservative

"Semiconservative" means the cell keeps the original, parental DNA each time replication takes place, while producing new DNA at the same time.

After replication, each DNA molecule has one parental strand and one daughter strand

Enzymes replicate the DNA

1. Enzymes called helicases unwind the DNA
2. DNA polymerase synthesize new DNA strands
3. Ligases join short strands into long strands

Complementary base pairing assures that the new DNA strands have the correct sequence

DNA replication requires lots of energy

ATP is required for every chemical reaction in DNA replication
-produce the nucleotides
-unwind the DNA
-build the new strands

Replication enzymes divide up the work

DNA replication begins simultaneously at multiple spots along the chromosomes, called origins of replication

Replication proceeds in both directions at once from each origin.

Prokaryotic cells divide by binary fission

In bacteria and archaea asexual reproduction occurs by binary fission a process that replicates DNA and distributes it to two daughter cells

binarry fission steps

1) parent cell contains one chromosome
2) DNA replicates and attaches to cell membrane
3) membrane growth between the two attachment points move the DNA moles apart as new cell wall material is deposited
4) the result of binary fission: two daughter cells each identical to the original

Prokaryotes can get new DNA

In bacteria and archaea a donor cell can directly transfer its genes to a recipient cell

Healthy cells can also absorb DNA from dead and dying cells and incorporate it into their genomes

Eukaryotic cell division

Must replicate entire genome

Chromatin

DNA is wrapped around histone proteins

Chromosomes

Highly condensed (compacted) chromatin

Chromosomes exist in pairs in humans

One set from maternal side, one set from parental side

Chromosome pairs contain the same genes= homologous

homologous chromosomes

Chromosomes that have the same sequence of genes and the same structure

In an undividing cell, the DNA is not condensed

Before replication the DNA is visible as chromatin

Chromosome duplication occurs during interphase

AFTER duplication, the DNA condenses into visible two sister chromatids (prophase)

Mitosis generates exact cell copies

Eukaryotes divide in a process called mitosis

Mitosis is one part of cell cycle

At the end of mitosis, two new daughter cells have exactly the same DNA as the new parent cell

The cell cycle is a repeated series of events

The cell cycle lasts from the beginning of one cell division until the beginning of the next

It includes the time when cells are dividing (mitosis) and the time when cells are not dividing (interphase)

G1 phase of cell cycle (1st)

Normal cell function and cell growth

If the cell is getting ready to divide, it will move to S phase if not it will stay in G1 phase

S phase of cell cycle (2nd)

DNA replication and duplication copying its entire genome- every chromosome

Now it is committed to dividing. There is no going back after replication begins

G2 phase of cell cycle (3rd)

Additional growth and preparation for division

Then...
Prophase
Metaphase
Anaphase
Telophase

Cell produces centrosomes (producing microtubules) necessary for mitosis

Mitosis (M phase) is eukaryotic cell division

Cells leaving G2 phase enter mitosis the cell division of the nucleus, which is then followed by cytokinesis the division of the cell itself

Prophase (1st stage of mitosis)

Chromosomes condense and spindle forms

Once the spindle forms. Chromosomes attach to it

Chromosome copies move towards the "poles" and synthesize microtubules

During interphase the cell is not dividing

Interphase proceeds in 3 stages
G1
S
G2

Metaphase (2nd stage of mitosis)

Chromosomes line up at the equator

Spindle forms

Spindle microtubules attach to the sister chromatids

Anaphase (3rd phase of mitosis)

Spindle separates the chromatids

Sister chromatids are pulled apart by mitotic spindle

Once separated, each chromatid is referred to as a chromosome

Cell elongates

The spindle shortens, moving the sister chromatids towards the opposite poles

Telophase (4th stage of mitosis)

Chromosomes unwind and spindle dissolves

Chromosomes de-condense

Nuclear membrane reforms

Microtubules begin to disintegrate

Two sets of protein filaments form at equatorial plane

Cytokinesis

Splits the cell

The cytoplasm and the two nuclei are distributed into the two forming daughter cells, which then physically separate.

Cytokinesis in animal cells

cleavage furrow forms

Proteins beneath the cell membrane contract like a draw string, separating the daughter cells

Cytokinesis in plant cells

A cell plate forms

The cell plate is the beginning of a new wall that separates the two daughter plant cells

Vesicles gather at the middle of the cell to deliver the necessary cellulose, other polysaccharides, and proteins

The ________ is under tight control

Cell cycle

A series of _________ regulate the cell cycle

Chemical checkpoints

Chemical checkpoints in cell cycle ensure that

All the DNA has replicated

DNA is not damaged

Chromosomes line up and separate properly

Apoptosis

programmed cell death

_______ cells divide out of control

Cancer

Tumor cells are
Benign:
Malignant:

Benign: contained

Malignant: spreadable