22 Questions
What is the composition by dry weight of the nucleus?
DNA 9%, RNA 1%, Histone Protein 11%, Residual Protein 14%, and Acidic Proteins 65%
What is the main site for enzyme activity in the nucleus?
Nucleoplasm
What are chromosomes made of?
Protein and a single molecule of DNA
How many chromosomes do humans have?
46
What is the term for the two chromosomes in a homologous pair that carry the same type of genetic information?
Homologues pairs
Which chromosomes determine a person's biological sex?
X and Y
What are telomeres?
Sections of DNA found at the ends of each chromosome
What is karyotyping used for?
To determine the chromosome complement of an individual
What is found at the ends of each chromosome to protect them?
$TTAGGG$ sequences forming telomeres
What is the name for the localized region of the chromosome with which spindle fibers attach?
$Centromere$
Which structure in the nucleus is related to the production of ribosomal RNA molecules and assembly of ribosomes?
Nucleolus
What makes up approximately 80% of the total chromosomal protein?
Histones
What is the primary function of the nucleus in a eukaryotic cell?
Storage of genetic material
Which organelle is known as the administrative center of the cell?
Nucleus
In which type of cells is it common to find no nucleus?
Blood cells
What percentage of the total cell volume does the average nucleus occupy in mammalian cells?
10%
Which type of cells are classified as polynucleated?
Liver cells
What determines the shape of the nucleus in a cell?
Shape of the cell
Which organelle has the largest cellular organelle in animal cells?
Nucleus
In which type of cells is it common to find more than one nucleus?
Liver cells
What is the average diameter of the nucleus in mammalian cells?
$6 \text{ μm}$
Which type of cells are classified as mononucleate?
$\text{Smooth muscle cells}$
Study Notes
- The nucleus is a membrane-enclosed organelle found in eukaryotic cells, serving as the information processing and administrative center.
- The nucleus is the largest cellular organelle, storing the cell's hereditary material (DNA) and coordinating cell activities.
- Cells contain one to multiple nuclei, depending on the type, and their shape and size can vary.
- The nucleus is surrounded by a nuclear envelope with inner and outer membranes, with nuclear pores controlling the movement of molecules.
- The nucleoplasm is a fluid substance within the nucleus, mainly composed of proteinaceous materials and enzymes, separated from the cytoplasm by the nuclear envelope.
- The nucleolus is a densely stained structure inside the nucleus, responsible for producing ribosomal RNA molecules and assembling ribosomes.
- Chromosomes are thread-like structures inside the nucleus, made of protein and DNA, with histones and non-histone proteins that determine gene activity.
- Humans have 46 chromosomes, including 22 autosomes and 2 sex chromosomes (X and Y), determining biological sex (XX for females and XY for males).
- Chromosomes consist of identical sister chromatids attached by the centromere, which divides chromosomes into short and long arms.
- Chromosomes have telomeres at their ends, made up of repeated DNA sequences and protective proteins, preventing chromosome shortening during replication.
- Techniques such as karyotyping are used to study human chromosomes and determine the chromosome complement of an individual.
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