Cell Division and Protein Synthesis

(pp. 81–87)

Cell life cycle

The series of changes a cell goes through from the time it is formed until it divides.

Interphase

The longer phase of the cell cycle where the cell grows and carries on its usual metabolic activities; resting only from division (also called the metabolic phase).

DNA Replication

The exact duplication of the genetic material (DNA molecules) that precedes cell division, occurring toward the end of interphase.

Mitosis

Division of the nucleus, resulting in the formation of two daughter nuclei with exactly the same genes as the mother nucleus.

Cytokinesis

Division of the cytoplasm, which usually begins during late anaphase and completes during telophase.

Prophase

The first stage of mitosis; chromatin coils into visible chromosomes (each made of two chromatids), centrioles move apart, mitotic spindle forms, and the nuclear envelope disappears.

Chromatid

One of the two identical strands making up a duplicated chromosome.

Centromere

A buttonlike body that holds two chromatids together.

Metaphase

The stage of mitosis where chromosomes cluster and line up at the metaphase plate (the center of the spindle).

Anaphase

The stage of mitosis where centromeres split, and the separated chromatids (now called chromosomes again) are pulled toward opposite ends of the cell.

Telophase

The final stage of mitosis where chromosomes uncoil back into chromatin, the spindle breaks down, and a nuclear envelope forms around each chromatin mass.

Cleavage furrow

A contractile ring made of microfilaments that forms over the midline of the spindle during cytokinesis, pinching the cytoplasmic mass into two parts.

Gene

A segment of DNA that carries the information for building one protein or polypeptide chain.

Triplet

Each sequence of three bases on the DNA gene that specifies one particular amino acid.

Ribonucleic Acid (RNA)

A second type of nucleic acid (single-stranded, uses ribose, contains uracil) that acts as a decoder and messenger for DNA.

Messenger RNA (mRNA)

Long, single nucleotide strands that carry the “message” (instructions for protein synthesis) from the DNA gene in the nucleus to the ribosomes in the cytoplasm.

Transfer RNA (tRNA)

Small, cloverleaf-shaped RNA molecules that transfer (ferry) amino acids to the ribosome.

Ribosomal RNA (rRNA)

RNA that helps form the ribosomes, where proteins are built.

Protein synthesis

Involves two major phases: transcription and translation.

Transcription

The phase of protein synthesis that involves the transfer of information from DNA’s base sequence into the complementary base sequence of mRNA (occurs in the nucleus).

Codons

The corresponding three-base sequences on mRNA that specify a particular amino acid.

Translation

The phase of protein synthesis where the language of nucleic acids (base sequence) is “translated” into the language of proteins (amino acid sequence) (occurs in the cytoplasm).

Anticodon

A special three-base sequence on the tRNA "head" that can bind to the complementary codon on mRNA