CH 3 - PT 3 Nucleus, Cell Cycle, DNA, and Protein Synthesis

What is the largest organelle in a cell?

The nucleus

What does the nucleus contain?

The genetic library of blueprints for synthesis of nearly all cellular proteins.

What type of cells are typically uninucleate?

Most cells are uninucleate, meaning they have one nucleus.

Which types of cells can be multinucleate?

Skeletal muscle cells, bone destruction cells, and some liver cells.

What type of cells are anucleate?

Mature red blood cells.

What are the three main structures of the nucleus?

Nuclear envelope, nucleoli, and chromatin.

What is the function of the nuclear envelope?

It is a double-membrane barrier that encloses the nucleoplasm and regulates transport.

What is the nucleoplasm?

The jelly-like fluid enclosed by the nuclear envelope.

What is the role of nucleoli?

Involved in ribosomal RNA (rRNA) synthesis and ribosome subunit assembly.

What is chromatin composed of?

30% DNA, 60% globular histone proteins, and 10% RNA chains.

What are nucleosomes?

Fundamental units of chromatin consisting of DNA wrapped around histones.

What happens to chromatin during cell division?

Chromatin condenses to form chromosomes.

What are the two major periods of the cell cycle?

Interphase and the mitotic phase.

What occurs during interphase?

The cell grows and carries out its usual activities in preparation for cell division.

What are the subphases of interphase?

G₁ (gap 1), S (synthesis), and G₂ (gap 2).

What occurs during the G₁ phase?

Vigorous growth and metabolism; cells that cease dividing are in this phase.

What happens during the S phase?

DNA replication occurs.

What is the function of the G₂ phase?

Preparation for cell division.

What is mitosis?

The process of nuclear division that distributes chromosomes to two daughter nuclei.

What are the phases of mitosis?

Prophase, metaphase, anaphase, and telophase.

What is the role of DNA polymerase in DNA replication?

It synthesizes new strands of DNA by bonding free nucleotides together.

What is the replication fork?

The area where hydrogen bonds between base pairs are broken and DNA strands separate.

What is the leading strand in DNA replication?

The strand synthesized toward the replication fork.

What is the lagging strand in DNA replication?

The strand synthesized away from the replication fork.

What is the significance of the G₁ checkpoint?

It is a restriction point that assesses whether the cell is ready to proceed with division.

What is the G₂/M checkpoint?

It occurs between G₂ and M phases to ensure the cell is ready for mitosis.

What is the structure of a chromosome during metaphase?

A chromosome consists of two sister chromatids.

What is the nuclear pore complex?

It regulates the transport of specific large molecules into and out of the nucleus.

What are the main phases of mitosis?

Prophase, Metaphase, Anaphase, Telophase.

What is cytokinesis?

The division of the cytoplasm.

What are the three subphases of interphase?

G1 (growth), S (growth and DNA synthesis), G2 (growth and final preparations for division).

What occurs during G1 phase?

The cell grows and the centrioles begin replicating.

What occurs during G2 phase?

The centrioles finish replicating and the cell completes preparations for mitosis.

What happens during early prophase?

Chromatin condenses into visible chromosomes, and centrosomes begin synthesizing microtubules.

What is the role of the mitotic spindle?

To push centrosomes to opposite poles of the cell and assist in chromosome separation.

What happens during late prophase?

The nuclear envelope breaks apart, and microtubules attach to kinetochores on chromosomes.

What is the metaphase plate?

The imaginary plane where centromeres of chromosomes align at the cell's equator.

What occurs during anaphase?

Centromeres split, and sister chromatids are pulled toward opposite poles of the cell.

What is the shortest phase of mitosis?

Anaphase.

What happens during telophase?

Chromosomes uncoil to form chromatin, new nuclear membranes form, and nucleoli reappear.

What initiates cytokinesis?

It begins during late anaphase and continues through mitosis.

How do daughter cells form during cytokinesis?

A ring of actin microfilaments contracts to form a cleavage furrow, pinching the two daughter cells apart.

What is the function of kinetochores?

To attach microtubules during mitosis and pull chromosomes to the cell's equator.

What happens to the nuclear envelope during late prophase?

It breaks apart, allowing the mitotic spindle to interact with chromosomes.

What are sister chromatids?

Identical threads of a duplicated chromosome held together at the centromere.

What is the role of polar microtubules?

To push against each other and move the poles of the cell farther apart.

What triggers the separation of chromatids at the end of metaphase?

Enzymes that are activated at the end of metaphase.

What happens to the spindle during telophase?

The spindle disappears.

What is chromatin?

The DNA-containing material in the form of a less condensed structure during interphase.

What is the significance of the G1 checkpoint?

It is a restriction point that assesses whether the cell is ready to proceed to DNA synthesis.

What occurs to the nucleoli during prophase?

The nucleoli disappear.

What happens to chromosomes during anaphase?

Each sister chromatid becomes a separate chromosome and is pulled toward opposite poles.

What is the main purpose of mitosis?

To distribute chromosomes to two daughter nuclei, producing two identical daughter cells.

What is interphase?

The phase during which the cell carries out normal metabolic activities and grows, consisting of G1, S, and G2 periods.

What occurs during the G1 phase of interphase?

The centrioles begin replicating.

What happens during the S phase of interphase?

DNA is replicated.

What is the purpose of mitosis?

To distribute chromosomes to two daughter nuclei, resulting in two identical daughter cells.

What is telophase?

The final phase of mitosis where chromosomes uncoil, nuclear envelopes form, and the mitotic spindle breaks down.

What is the role of messenger RNA (mRNA)?

To carry instructions from DNA for building proteins, maintaining the triplet code from DNA.

What is transcription?

The process where DNA information is copied into mRNA.

What is the difference between exons and introns?

Exons are coding segments of a gene, while introns are noncoding segments interspersed among exons.

What are the three types of RNA involved in protein synthesis?

Messenger RNA (mRNA), Ribosomal RNA (rRNA), and Transfer RNA (tRNA).

What is the function of ribosomal RNA (rRNA)?

To serve as a structural component of ribosomes, aiding in the translation of mRNA into polypeptides.

What is the function of transfer RNA (tRNA)?

To carry specific amino acids and match them with the corresponding codon on mRNA during translation.

What is the genetic code?

The set of rules by which information encoded in mRNA is translated into proteins, consisting of codons.

How many possible codons are there?

64 possible codons, derived from 4 bases (A, U, C, G) in groups of three.

What is the significance of redundancy in the genetic code?

It helps protect against transcription errors by allowing multiple codons to code for the same amino acid.

What is the process of translation?

The decoding of mRNA to assemble polypeptides, occurring at ribosomes in the cytoplasm.

What happens during the initiation stage of transcription?

RNA polymerase binds to the promoter and begins mRNA synthesis.

What occurs during the elongation stage of transcription?

RNA polymerase moves along the template strand, adding RNA nucleotides complementary to the DNA.

What signals the termination of transcription?

A special nucleotide sequence called a termination signal.

What is the role of the nuclear envelope in protein synthesis?

It regulates the exit of mRNA from the nucleus to the cytoplasm for translation.

What is the triplet code?

A sequence of three nitrogen bases in DNA that specifies a single amino acid.

What is the function of the cleavage furrow during cytokinesis?

To pinch the cell apart, resulting in two identical daughter cells.

What is the final outcome of mitosis and cytokinesis?

Two identical daughter cells that are genetically identical to the original mother cell.

What is the structure of mRNA?

Single-stranded, with a sequence that is complementary to the DNA template strand.

Where does protein synthesis occur?

At ribosomes in the cytoplasm.

What is the role of the promoter in transcription?

It is the region where RNA polymerase binds to initiate transcription.

What is the significance of the termination signal in transcription?

It marks the end of mRNA synthesis and leads to the release of RNA polymerase and the mRNA transcript.

What is the start codon in the genetic code?

AUG

What are the stop codons in the genetic code?

UAA, UAG, UGA

What is the role of tRNA in translation?

tRNA molecules recognize and bind to specific codons on mRNA and carry the corresponding amino acids.

What are the three phases of translation?

Initiation, Elongation, and Termination.

What happens during the initiation phase of translation?

The small ribosomal subunit binds to the mRNA and the initiator tRNA carrying methionine, followed by the large ribosomal subunit joining.

What occurs during the elongation phase of translation?

Amino acids are added one at a time to the growing polypeptide chain through codon recognition, peptide bond formation, and translocation.

What is the function of the release factor during termination?

It binds to the stop codon, causing the release of the polypeptide chain and the disassembly of the ribosome.

What is the relationship between DNA triplets and mRNA codons?

mRNA codons are complementary to the DNA triplets, with thymine (T) replaced by uracil (U) in RNA.

Which amino acid is coded by the codon AUG?

Methionine (Met), which also serves as the start codon.