Cell Biology and Genetics: Lysosomes, Nucleus, DNA, and Protein Synthesis

What is the primary difference between a primary lysosome and a secondary lysosome?

A primary lysosome is produced by the Golgi complex and contains inactive enzymes, while a secondary lysosome is formed when a primary lysosome fuses with an endosome or organelle, activating its enzymes for digestion.

What is the nucleus and what is its primary function?

The nucleus is the largest organelle in the cell, containing the cell's genetic material and regulating gene expression.

What is the composition of the nuclear envelope?

The nuclear envelope is a double membrane perforated by nuclear pores, which are formed by a ring of proteins called the nuclear pore complex.

What is the function of the nuclear lamina?

The nuclear lamina supports the nuclear envelope and helps maintain the shape of the nucleus.

What is nucleoplasm?

Nucleoplasm is the material within the nucleus, consisting of chromatin and nucleoli.

What is the role of the nucleolus?

The nucleolus produces ribosomal RNA (rRNA) and ribosomal subunits, essential for protein production in the cytoplasm.

How many chromosomes do most human cells contain?

Most human cells contain 46 chromosomes, organized into 23 pairs.

What are the three components of a nucleotide?

A nucleotide consists of a sugar (deoxyribose), a phosphate group, and a nitrogenous base.

What are the four nitrogenous bases found in DNA?

The four nitrogenous bases in DNA are adenine (A), thymine (T), cytosine (C), and guanine (G).

What is the structure of DNA?

DNA has a double helix shape, resembling a spiral staircase, with a backbone of alternating phosphate groups and deoxyribose.

What is the law of complementary base pairing in DNA?

The law states that adenine pairs with thymine (A-T) and guanine pairs with cytosine (G-C) through hydrogen bonds.

What is a gene?

A gene is a segment of DNA that codes for the synthesis of a specific protein and is considered the functional unit of heredity.

What percentage of human DNA is coding DNA?

About 2% of human DNA is coding DNA, while the remaining 98% is non-coding DNA that plays roles in chromosome structure and gene regulation.

What is chromatin?

Chromatin is the complex of DNA and proteins (histones) that organizes DNA within the nucleus, existing as 46 chromosomes during cell division.

What happens to chromatin during mitosis?

During mitosis, chromatin condenses into tightly packed chromosomes, making it visible under a light microscope.

What is the average length of a human DNA molecule?

The average human DNA molecule is about 2 inches long.

What are purines and pyrimidines?

Purines (adenine and guanine) have a double-ringed structure, while pyrimidines (cytosine, thymine, and uracil) have a single-ringed structure.

What is the significance of uracil in RNA?

Uracil is a nitrogenous base found only in RNA, replacing thymine found in DNA.

How does DNA organize itself with proteins?

DNA organizes itself with proteins called histones to form chromatin, which condenses into chromosomes during cell division.

What is the role of ribosomes in protein synthesis?

Ribosomes, composed of rRNA and proteins, are essential for translating mRNA into proteins in the cytoplasm.

What types of cells are anuclear?

Anuclear cells, such as erythrocytes (red blood cells), lack a nucleus.

What types of cells are multinuclear?

Multinuclear cells, such as skeletal muscle cells, contain multiple nuclei.

What are histones?

Proteins around which DNA winds, clustering in groups of eight molecules.

What is a nucleosome?

DNA wrapped around histones.

How much thicker and shorter is chromatin compared to naked DNA?

Chromatin is 150 times thicker and 1,000 times shorter than naked DNA.

What is DNA replication?

The process of copying DNA to make another molecule of DNA.

What are sister chromatids?

Two parallel filaments of identical DNA that are joined at a constricted centromere.

What role do kinetochores play in cell division?

They are protein plaques on each side of the centromere that assist in cell division.

What is the general structure of RNA?

RNA contains ribose sugar, bases A, U, G, C, and is a single nucleotide chain.

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

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

What is the current definition of a gene?

An information-containing segment of DNA that codes for the production of RNA, often involved in synthesizing proteins.

What is the process of transcription?

The copying of genetic instructions from DNA to mRNA using RNA polymerase.

What happens during the processing of pre-mRNA?

Introns are removed and exons are spliced together to form mature mRNA.

What is the role of ribosomes in translation?

Ribosomes read the mRNA code and form a protein.

What is the function of transfer RNA (tRNA)?

tRNA delivers a single amino acid to the ribosome and contains an anticodon complementary to the mRNA codon.

What are the three main steps in translation?

Initiation, elongation, and termination.

What is the start codon in mRNA?

AUG, which codes for the amino acid methionine.

What is the significance of the protein cap on mRNA?

It serves as a recognition site for ribosomes during translation.

What is the difference between transcription and translation?

Transcription is the process of making mRNA from DNA, while translation is converting mRNA into a protein.

What is meant by 'semi-conservative fashion' in DNA replication?

Each new DNA molecule consists of one original strand and one newly synthesized strand.

What is the role of the terminator in transcription?

It is a stop sequence on DNA that signals the end of gene transcription.

What is the function of exons in RNA?

Exons are the RNA sequences that will be expressed in the final protein product.

What is the relationship between DNA, RNA, and proteins?

DNA is transcribed to RNA, which is then translated into proteins.

What does it mean for a gene to be activated?

It means that the gene is being expressed, resulting in the production of mRNA and subsequently a protein.

What is the role of tRNA during elongation in translation?

tRNA carries amino acids and binds to the A site of the ribosome.

What happens to the ribosome during the elongation phase of translation?

The ribosome creates a peptide bond between the first and second amino acids and moves down the mRNA by one codon.

What triggers the termination of translation?

The ribosome reaches a stop codon on the mRNA.

What is the function of the release factor in translation?

The release factor binds to the A site, prompting the ribosome to disassemble from the mRNA.

How are proteins modified for secretion or lysosomal targeting?

Proteins are synthesized into the rough endoplasmic reticulum (ER) and modified by enzymes.

What are polyribosomes?

Clusters of multiple ribosomes translating the same mRNA molecule simultaneously.

What is the first step in protein processing after translation?

Post-translational modification occurs as the protein threads through a pore into the rough ER.

What occurs during the Golgi complex processing of proteins?

Vesicles fuse to form a new Golgi cistern, which migrates and packages proteins into secretory vesicles.

How can gene expression be regulated in cells?

Genes can be turned on or off, and their expression can vary based on chemical messengers like hormones.

What is the role of prolactin in casein synthesis?

Prolactin binds to receptors on mammary cells, activating a regulatory protein that initiates transcription of the casein gene.

What are the four steps of DNA replication?

1. Unwinding the helix, 2. Unzipping the helix, 3. Synthesizing complementary strands, 4. Organizing new DNA into nucleosomes.

What is semiconservative replication?

Each new DNA molecule contains one old (parental) strand and one newly synthesized strand.

What are the phases of the cell cycle?

Interphase (G1, S, G2) and the mitotic phase (prophase, metaphase, anaphase, telophase).

What occurs during the G1 phase of interphase?

The cell carries out normal tasks and synthesizes proteins in preparation for DNA replication.

What happens during the S phase of interphase?

The cell replicates all nuclear DNA and duplicates centrioles.

What is the significance of the G0 phase?

Cells in G0 have left the cycle and cease dividing for a long time or permanently.

What is the primary function of mitosis?

To produce two genetically identical daughter cells.

What occurs during prophase of mitosis?

Genetic material condenses into chromosomes, the nuclear envelope disintegrates, and spindle fibers form.

What is the role of spindle fibers during metaphase?

Spindle fibers align chromosomes along the cell equator.

What happens during anaphase?

Sister chromatids are cleaved apart and migrate to opposite poles of the cell.

What occurs during telophase?

Chromosomes cluster at each pole, the nuclear envelope reforms, and chromosomes uncoil.

What is cytokinesis?

The division of the cytoplasm into two cells, beginning in late anaphase and continuing through telophase.

What factors stimulate cell division?

Sufficient cytoplasm, replicated DNA, adequate nutrients, and growth factors.

What is cancer in relation to cell division?

Cancer involves malignant tumors that invade surrounding tissues and can metastasize to form secondary tumors.

What are the lethal effects of cancer?

Cancer can replace functional tissue, invade vital organs, weaken immunity, and cause severe wasting of tissues.