Unit 5: Information Transfer

Cell Division and Mitosis

Interphase

Longest phase of the cell cycle (includes G₁, S, and G₂ phases).

G₁ phase:

Cell grows and performs normal functions.

S phase

DNA is replicated (each chromosome duplicates into sister chromatids).

G₂ phase

Cell prepares for mitosis (makes organelles and proteins).

Phases of Mitosis

IPMAT

Prophase

Chromosomes condense, nuclear membrane dissolves, spindle fibers form.

Metaphase

Chromosomes line up in the middle of the cell.

Anaphase

Sister chromatids are pulled apart to opposite poles.

Telophase

Nuclear envelopes reform; chromosomes begin to uncoil

Cytokinesis in plant cells

A cell plate forms between new nuclei → becomes a cell wall.

Cytokinesis in animal cells

The cell pinches inward using a cleavage furrow.

Cancer

Uncontrolled cell division caused by DNA mutations.

Tumors

Abnormal masses of cells.

Benign tumors

Do not spread

Malignant tumors

Invade tissues, can metastasize (spread through blood/lymph)

Chromatin

Unwound DNA (in interphase).

Chromosomes

Tightly coiled DNA, visible during mitosis/meiosis

Chromatid

One of two identical "sister" parts of a duplicated chromosome.

Meiosis I

Homologous chromosomes separate.

Prophase I

Crossing over occurs (exchange of genes between homologous chromosomes → increases genetic diversity).

Meiosis II

Sister chromatids separate (like mitosis).

results of meiosis

4 genetically unique haploid gametes

Somatic cells

Body cells (diploid, 2n) → undergo mitosis.

Gametes

Sex cells (sperm/egg, haploid, n) → made by meiosis.

Dominant alleles

Always show in phenotype if present

Recessive alleles

Only show when homozygous.

Genotype

Genetic makeup

Phenotype

Physical trait

Complete Dominance

Dominant allele completely masks recessive

Incomplete Dominance

Blending (e.g., red + white = pink flowers).

Codominance

Both alleles show (e.g., red + white = red and white spotted cow).

DNA & RNA are nucleic acids made up of

nucleotides

Each nucleotide has:

• Sugar (deoxyribose in DNA, ribose in RNA)

• Phosphate group

• Nitrogen base

DNA base pairing

A ↔ T, C ↔ G

RNA base pairing

A ↔ U, C ↔ G

mRNA

Carries code from DNA to ribosome.

tRNA

Brings amino acids to ribosome.

rRNA

Makes up the ribosome, helps read mRNA

Transcription

(in nucleus):

• DNA is used to make mRNA.

• RNA polymerase helps build the mRNA strand from DNA template.

Translation

in cytoplasm at ribosome):

• mRNA is read in codons (3-base groups).

• tRNA brings amino acids matching codons using anticodons.

• Ribosome links amino acids → polypeptide (protein).

Point mutation

One base changed (may be silent, missense, or nonsense).

Frameshift mutation

• Insertion/deletion changes reading frame.

• Causes: Radiation, chemicals, replication errors.