Chromosomes and Cell Cycle Quiz

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Questions and Answers

What are chromatids?

Structures that break down chromosomal material

Identical strands formed from DNA replication (correct)

Segments of non-coding DNA

Different types of chromosomes in a cell

Which structures are responsible for the majority of DNA in living organisms?

Histones

Chromatin

Chromosomes (correct)

Nucleosomes

What is the role of the centromere in chromosomes?

It packages DNA with proteins

It protects the ends of chromosomes

It joins sister chromatids together (correct)

It is the site of DNA transcription

During which phase of the cell cycle are chromosomes maximally contracted and visible?

Metaphase Signup and view all the answers

What is the study of chromosomes and chromosomal abnormalities referred to?

Cytogenetics Signup and view all the answers

Which of the following characteristics is true for heterochromatin?

Silenced genes and more condensed Signup and view all the answers

What role do telomeres play at the ends of chromosomes?

They shorten with each cell division, acting like a biological clock Signup and view all the answers

What type of chromosome structure is characterized by a centromere located in the middle, resulting in two equal arms?

Metacentric Signup and view all the answers

Which statement regarding centromeres is correct?

They attach spindle fibers to pull chromatids apart during mitosis Signup and view all the answers

In a submetacentric chromosome, how do the lengths of the two arms compare?

The short arm is shorter than the long arm Signup and view all the answers

What type of chromosome has arms that are of equal length?

Metacentric Signup and view all the answers

What is the total number of chromosomes found in a normal human cell nucleus?

46 Signup and view all the answers

Which of the following statements best describes homologous chromosomes?

They consist of one chromosome from each parent. Signup and view all the answers

How many pairs of sex chromosomes do humans possess?

1 Signup and view all the answers

What role do satellites play in the chromosome structure?

They play a vital role in nucleolus formation. Signup and view all the answers

What are the two categories of chromosomes based on structure?

Autosomes and Allosomes Signup and view all the answers

In humans, what designation is given to the sex chromosomes?

X and Y Signup and view all the answers

What is the total number of autosomes in a human cell?

22 Signup and view all the answers

What is the ploidy level of human somatic cells?

Diploid (2n) Signup and view all the answers

Where does ribosome synthesis and assembly primarily occur?

In the nucleolus Signup and view all the answers

Study Notes

Chromosomes: Structure, Types, and Classification

Chromosomes are the organized genetic structures within a living organism, containing most of the DNA.
The term "chromosome" derives from the Greek words "chroma" (color) and "soma" (body).
Chromosomes are responsible for distinguishing species and transmitting genetic information between generations.
They are visible under a light microscope during metaphase of mitosis, when maximally contracted.

Chromosome Structure

A chromosome is composed of two identical sister chromatids, resulting from DNA replication during the S phase (synthesis) of the cell cycle.
Sister chromatids are joined at a primary constriction called the centromere.
DNA is complexed with proteins (histones) and other macromolecules. This complex is known as chromatin.
Chromatin is packaged into nucleosomes, which are further organized into higher order structures. Different levels of chromatin packaging are visible: DNA duplex, 11 nm diameter histone fiber, 30 nm chromatin fiber, 300 nm coiled chromatin fiber and 1400 nm diameter metaphase chromatid.
Chromatin exists differently in different cell types, with some cells lacking chromatin as part of their normal structure (e.g. erythrocytes).

Heterochromatin and Euchromatin

Heterochromatin is more condensed, gene-poor (contains more AT sequences) and stains darker in microscopic examination.
Euchromatin is less condensed, gene-rich (contains more GC sequences) and stains lighter.

Chromosome Tips and Middle

Telomeres are the tips of chromosomes. They act like a biological clock, getting shorter with each cell division.
Centromeres are the middle sections of chromosomes. They play a critical role for attaching to spindle fibers and pulling apart sister chromatids in cell division.
Each centromere divides the chromosome into a short arm (p) and a long arm (q).

Kinetochore

The kinetochore is a protein structure attached to each side of the centromere. It's critical for chromosome movement during cell division.

Chromosome Classification

Classification of Chromosomes based on gene complement.
- Autosomes: 22 pairs that control somatic characteristics.
- Allosomes (sex chromosomes): 1 pair controlling gender determination.
Classification based on centromere position.
- Metacentric: centromere in the middle, equal arms
- Submetacentric: centromere slightly off centre, unequal but similar length arms
- Acrocentric: centromere very near one end, very short p arm
- Telocentric: centromere at the end of the chromosome, no p arm
Classification of chromosomes based on length.
- Autosomes are numbered from 1-22 and classified in 7 groups (A to G) based on length, in descending order.
- Sex chromosomes either X & Y belong to group C&G respectively.

Satellites

Some chromosomes have satellite structures; these play a role in forming the nucleolus after cell division, a site of ribosome synthesis and assembly.

Chromosome Duplication

In preparation for cell division, DNA replicates, creating chromosomes composed of two identical sister chromatids joined by a centromere.

Chromosome Numbers

Members of the same species have identical chromosome numbers in somatic cells.
All chromosomes, except the sex chromosomes, are arranged in pairs based on identical length and position of the centromere.

Telomere

Telomeres are essential for protecting chromosome integrity and preventing fusion.
Telomeres are composed of repeating DNA sequences (TTAGGG) telomerase is the enzyme responsible for maintaining telomere length during DNA replication.
Telomerase is often found in stem cells and cancer cells because their division rate is high. This allows telomeres to remain long and therefore cells continually divide.
Shortening of telomeres is linked to aging. Cancer development may occur from telomerase activity.

Telomere and Cancer

Cancer cells often have high telomerase activity. This ensures the telomere remains long and that the cell can continue dividing. This allows cancer cells to bypass the normal mechanism for inhibiting uncontrolled cell division.
Research explores ways to directly target telomerase as a potential cancer treatment approach.

Telomerase

Telomerase is an enzyme that adds bases to telomeres. This maintains the length during cell division.
Telomerase is present in germ cells, stem cells, and highly active in cancer cells; this is one of the key characteristics of cancer cells enabling them to proliferate.
Measuring telomerase levels might become useful in cancer detection.

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Description

Test your knowledge on chromosomes, their structures, and roles during the cell cycle. This quiz covers key concepts such as chromatids, centromeres, and chromosomal abnormalities. Challenge yourself with questions related to the organization and function of genetic material in living organisms.