Cell Reproduction and Cell Cycle - Section 1

Cell Reproduction

The process by which cells produce new cells through mitosis , meiosis and cytokinesis.

Why do cells reproduce?

For growth, tissue repair, replacement of old cells, and reproduction.

Mitosis

Division of the nucleus that produces two genetically identical daughter cells.

Cytokinesis

Division of the cytoplasm to form two separate daughter cells.

Difference between mitosis and cytokinesis

Mitosis divides the nucleus; cytokinesis divides the cytoplasm.

Why are cells produced by mitosis called clones?

Because they have the same genetic information as the parent cell.

Why doesn't mitosis create genetic variation?

Because daughter cells are genetically identical.

Meiosis

A type of cell division that produces gametes and creates genetic variation.

Why does meiosis reduce the chromosome number by half?

So fertilization restores the normal diploid chromosome number.

Interphase

stage before meiosis and mitosis

G1 Phase

The cell grows and performs its normal functions.

S Phase

DNA is replicated (copied). DNA synthesis

G2 Phase

a check point to make sure the cell is good to go

What are the three phases of Interphase?

G1, S, and G2.

During which phase is DNA replicated?

S Phase and it duplicated

Interphase occurs...

Before mitosis or meiosis.

Interkinesis

Short period between Meiosis I and II where DNA is NOT replicated.

Why is Interkinesis NOT considered Interphase?

Because DNA is not replicated.

DNA synthesis

The DNA strand zips open and a new strand is synthesized to bind with the old one

When does DNA replication occur?

During S Phase.

DNA "unzips"

The two DNA strands separate so each can serve as a template.

Semiconservative Replication

Each new DNA molecule contains one original strand and one newly synthesized strand.

Why is DNA replication called semiconservative?

Because each daughter DNA molecule contains one old strand and one new strand.

Adenine pairs with...

Thymine (A-T).

Cytosine pairs with...

Guanine (C-G).

Chromatin

Uncondensed DNA found during Interphase.

When are chromosomes NOT visible?

During Interphase because DNA is chromatin.

When do chromosomes become visible?

During Prophase when chromatin condenses.

Histones

Proteins DNA wraps around to organize and package DNA.

Core Histones

Proteins DNA wraps around to form nucleosomes.

H1 Histone

Helps pack nucleosomes closer together.

Nucleosome

DNA wrapped around histone proteins; the basic unit of chromatin.

What is the basic unit of chromatin and eukaryotic cells?

Nucleosome.

Chromosome

A condensed DNA molecule containing genetic information.

Unduplicated Chromosome

One chromosome

Duplicated Chromosome

One chromosome consisting of two sister chromatids joined at the centromere.

Chromatid

One identical copy of a duplicated chromosome.

Centromere

The region where sister chromatids are attached.

Monad

Another name for one chromatid (DNA strand).

Dyad

Another name for a duplicated chromosome.

Chromatid = __ = __

DNA strand = Monad.

Dyad = __

Duplicated chromosome.

How many chromatids are in an unduplicated chromosome?

One.

How many chromatids are in a duplicated chromosome?

Two.

How many centromeres does a duplicated chromosome have?

One.

A duplicated chromosome is considered how many chromosomes?

One chromosome.

Does DNA replication increase chromosome number?

No. It doubles the chromatids, not the chromosomes.

Unless specified otherwise, assume chromosomes are...

Duplicated.

Homologous Chromosomes

A pair of chromosomes with the same genes but possibly different alleles.

Karyotype

An organized picture of an individual's chromosomes used to detect abnormalities.

Application: A cell finishes dividing its nucleus but remains one cell. What process failed?

Cytokinesis.

Application: A cell is actively copying its DNA. Which phase is it in?

S Phase.

Application: A cell has copied its DNA and is preparing to divide. Which phase?

G2 Phase.

Application: DNA replication failed. Which phase malfunctioned?

S Phase.

Application: Why are chromosomes not visible during Interphase?

Because DNA is in the form of chromatin.

Application: During what phase do chromosomes first become visible?

Prophase.

Application: A chromosome has two chromatids and one centromere. How many chromosomes?

One chromosome.

Application: A chromosome has one chromatid. Is it duplicated or unduplicated?

Unduplicated.

Application: A chromosome has two chromatids. Is it duplicated or unduplicated?

Duplicated.

Application: If a duplicated chromosome separates in mitosis, what does each daughter cell receive?

One unduplicated chromosome.

Application: What happens if cytokinesis does not occur after mitosis?

One cell with two nuclei.

Application: Doctors arrange all of a patient's chromosomes to check for disorders. What is this?

A karyotype.

Professor Fact: Cells produced by mitosis are...

Genetically identical (clones).

Professor Fact: Meiosis creates...

Genetic variation.

Professor Fact: DNA is synthesized ONLY during...

S Phase.

Professor Fact: DNA strands = Chromatids = __

Monads.

Professor Fact: Dyad = __

Duplicated chromosome.

Professor Fact: Is a duplicated chromosome one or two chromosomes?

STILL one chromosome.

Professor Fact: Chromosome number after DNA replication...

Does NOT change.

Professor Fact: DNA replication doubles __ but not __

Chromatids; chromosomes.

Professor Fact: Why is Interkinesis NOT Interphase?

Because DNA is not replicated.