Podcast
Questions and Answers
What are chromatids?
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?
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?
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?
During which phase of the cell cycle are chromosomes maximally contracted and visible?
What is the study of chromosomes and chromosomal abnormalities referred to?
What is the study of chromosomes and chromosomal abnormalities referred to?
Which of the following characteristics is true for heterochromatin?
Which of the following characteristics is true for heterochromatin?
What role do telomeres play at the ends of chromosomes?
What role do telomeres play at the ends of chromosomes?
What type of chromosome structure is characterized by a centromere located in the middle, resulting in two equal arms?
What type of chromosome structure is characterized by a centromere located in the middle, resulting in two equal arms?
Which statement regarding centromeres is correct?
Which statement regarding centromeres is correct?
In a submetacentric chromosome, how do the lengths of the two arms compare?
In a submetacentric chromosome, how do the lengths of the two arms compare?
What type of chromosome has arms that are of equal length?
What type of chromosome has arms that are of equal length?
What is the total number of chromosomes found in a normal human cell nucleus?
What is the total number of chromosomes found in a normal human cell nucleus?
Which of the following statements best describes homologous chromosomes?
Which of the following statements best describes homologous chromosomes?
How many pairs of sex chromosomes do humans possess?
How many pairs of sex chromosomes do humans possess?
What role do satellites play in the chromosome structure?
What role do satellites play in the chromosome structure?
What are the two categories of chromosomes based on structure?
What are the two categories of chromosomes based on structure?
In humans, what designation is given to the sex chromosomes?
In humans, what designation is given to the sex chromosomes?
What is the total number of autosomes in a human cell?
What is the total number of autosomes in a human cell?
What is the ploidy level of human somatic cells?
What is the ploidy level of human somatic cells?
Where does ribosome synthesis and assembly primarily occur?
Where does ribosome synthesis and assembly primarily occur?
Flashcards
What is a chromosome?
What is a chromosome?
A chromosome is a tightly packaged and organized structure containing most of a living organism's DNA.
What are sister chromatids?
What are sister chromatids?
Sister chromatids are identical copies of a replicated chromosome held together at the centromere.
What is the centromere?
What is the centromere?
The centromere is the constricted region where sister chromatids are joined.
What is chromatin?
What is chromatin?
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What is a nucleosome?
What is a nucleosome?
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Heterochromatin
Heterochromatin
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Euchromatin
Euchromatin
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Telomeres
Telomeres
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Centromere
Centromere
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Kinetochore
Kinetochore
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Metacentric chromosome - What is its centromere location?
Metacentric chromosome - What is its centromere location?
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Submetacentric chromosome - What is its centromere location?
Submetacentric chromosome - What is its centromere location?
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How are autosomes classified into groups?
How are autosomes classified into groups?
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What are sex chromosomes?
What are sex chromosomes?
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What is the human chromosomal complement?
What is the human chromosomal complement?
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What are homologous chromosomes?
What are homologous chromosomes?
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What are somatic cells?
What are somatic cells?
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What are gametes?
What are gametes?
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What are satellites in chromosomes?
What are satellites in chromosomes?
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What is the role of the nucleolus?
What is the role of the nucleolus?
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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
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Classification of Chromosomes based on gene complement.
- Autosomes: 22 pairs that control somatic characteristics.
- Allosomes (sex chromosomes): 1 pair controlling gender determination.
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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
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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
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Telomeres are essential for protecting chromosome integrity and preventing fusion.
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Telomeres are composed of repeating DNA sequences (TTAGGG) telomerase is the enzyme responsible for maintaining telomere length during DNA replication.
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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.
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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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