unit 5 cell cycle and DNA replication

What is the cell cycle?

The series of events a cell goes through as it grows, replicates its DNA, and divides.

Why do cells divide?

For growth, repair, replacement, and asexual reproduction.

Interphase

The phase where a cell spends ~90% of its life performing normal functions and preparing to divide.

G0 phase

Resting phase; cell exits the cell cycle and does not divide.

G1 phase

Cell grows and prepares for DNA replication by synthesizing proteins and enzymes.

S phase

DNA synthesis; genetic material is replicated.

G2 phase

Cell grows and prepares for division; doubles contents and checks DNA.

M phase

The phase that includes mitosis and cytokinesis.

Mitosis

Nuclear division producing two identical nuclei.

Cytokinesis

Division of the cytoplasm into two daughter cells.

Cleavage furrow

Indentation that forms during cytokinesis in animal cells.

Cell plate

Structure that forms during cytokinesis in plant cells.

Apoptosis

Programmed cell death that occurs in a controlled manner.

How is the cell cycle regulated?

By cyclins, checkpoints, and proteins that monitor DNA damage and spindle attachment.

Cyclins

Proteins that regulate the timing and progression of the cell cycle.

Checkpoints

Control points that ensure conditions are favorable before progressing.

G1 checkpoint

Checks cell size, nutrients, growth factors, and DNA damage.

G2 checkpoint

Checks for DNA damage before mitosis begins.

Spindle checkpoint- Metaphase

Ensures chromosomes are properly attached to spindle fibers.

What happens when regulation fails?

The cell may become cancerous due to uncontrolled division.

Cancer

A disease caused by uncontrolled cell division due to gene mutations.

Mutagen

An environmental agent that causes mutations (e.g., radiation).

Carcinogen

An agent that causes cancer (e.g., tobacco tar).

Oncogene

A mutated proto-oncogene that promotes uncontrolled cell division.

Tumor suppressor gene

A gene that normally slows or stops cell division.

Effect of tumor suppressor mutation

Loss of function leads to uncontrolled division.

Effect of oncogene mutation

Gain of function causes checkpoint failure and rapid division.

How is cancer treated?

Surgery, radiation, chemotherapy, biologics, immunotherapy, and RNAi.

Why does chemotherapy cause hair loss?

It targets rapidly dividing cells, including hair follicles.

Chromatin

Spaghetti-like form of DNA during interphase.

Chromosome

A condensed structure of DNA made of two sister chromatids.

Chromatid

One identical half of a replicated chromosome.

Sister chromatids

Identical DNA strands joined at the centromere.

Centromere

Region where sister chromatids are joined.

Telomere

End regions of a chromosome.

Spindle fibers

Microtubules that move chromosomes during mitosis.

Centriole

Organelle that helps form spindle fibers in animal cells.

Prophase

Chromatin condenses, nuclear membrane breaks down, spindle fibers form.

Metaphase

Chromosomes line up at the MIDDLE of the cell.

Anaphase

Sister chromatids separate and move AWAY to opposite poles.

Telophase

TWO Nuclear envelopes reform; chromosomes unwind.

Nucleic acids

Molecules that store and transmit genetic information.

Monomer of nucleic acids

Nucleotide.

Nucleotide components

Sugar, phosphate group, nitrogenous base.

DNA sugar

Deoxyribose.

RNA sugar

Ribose.

DNA bases

A, T, C, G.

RNA bases

A, U, C, G.

Double helix

The twisted ladder structure of DNA.

Complementary base pairing

A-T and G-C.

Anti-parallel DNA

Two strands run in opposite directions (5’→3’ and 3’→5’).

Type of bonds in DNA

Covalent bonds in backbone, hydrogen bonds between bases.

Why DNA replicates

So each daughter cell gets a complete copy of genetic information.

DNA replication model

Semi-conservative.

Semi-conservative replication

Each new DNA molecule contains one old strand and one new strand.

DNA helicase

Unzips DNA strands at the replication fork.

Replication fork

Area where DNA strands separate.

Primase

Adds RNA primer to start replication.

DNA polymerase III

Adds nucleotides in the 5’→3’ direction.

DNA polymerase I

Removes RNA primers and replaces them with DNA.

DNA ligase

“glues” Okazaki fragments together.

Leading strand

Continuously synthesized toward the replication fork.

old strand 3’ to 5’ into fork

Lagging strand

Discontinuously synthesized away from the fork.

old strand 5’ to 3’ into fork

Okazaki fragments

Short DNA fragments formed on the lagging strand.

What can go wrong during replication

Mutations from errors or environmental damage.

Human DNA replication speed

~50 nucleotides per second.

Cancer is contagious

False.

Cancer is a single disease

False; it includes over 100 diseases.

Cancer caused by abnormal genes

True.

What phase is this?

Interphase

What phase is this?

Prophase

What phase is this?

Metaphase

What phase is this?

Anaphase

What phase is this?

Telophase

What is this phase called?

Cytokinesis

RNA

helps convert DNA message into proteins

DNA

stores genetic information