What are the DNA structures at the ends of chromosomes?
The DNA structures at the ends of eukaryotic chromosomes The sequence organisation of the telomeric regions is extremely similar for all eukaryotes examined to date. Subtelomeric areas may contain large sequence arrays of middle repetitive, complex elements that sometimes have similarities to retrotransposons.
What is the structure of eukaryotic chromosomes?
Eukaryotic Chromosome Structure. 1. Eukaryotic chromosomes are found in the cell’s nucleus. The principal feature that distinguishes a eukaryotic cell from a prokaryotic cell is the presence of a membrane-bound nucleus. This nucleus is the “control center” of the cell that stores all the cell’s genetic information, or DNA.
What are the characteristics of chromosomal regions?
Chromosomal characteristics. Telomere: Used to maintain chromosomal integrity by capping off the ends of the linear chromosomes. This region is a microsatellite, but its function is more specific than a simple tandem repeat. Throughout the eukaryotic kingdom, the overall structure of chromosome ends is conserved and is characterized by...
What is the centromere of a chromosome?
Clarification: Centromere is the region in the eukaryotic chromosome where kinetochore is assembled and sister chromatids are held together. In some cases, centromere can also be located at the end of the chromosomes. 3. Which of the following is less condensed, less stained portion of chromatin?
What is found at the ends of the chromosomes in eukaryotes and why?
Repetitive regions at the very ends of chromosomes are called telomeres, and they're found in a wide range of eukaryotic species, from human beings to unicellular protists. Telomeres act as caps that protect the internal regions of the chromosomes, and they're worn down a small amount in each round of DNA replication.
What is found at the end of chromosomes?
Telomeres are structures made from DNA sequences and proteins found at the ends of chromosomes. They cap and protect the end of a chromosome like the end of a shoelace. In almost all animals, from the simplest to the most complex, telomeres are required for cell division.
Do the ends of eukaryotic chromosomes have genes?
These areas contain very few genes and are thought to be organised into a heterochromatin-like domain. The terminal regions almost invariably consist of short, direct repeats.
What is the end of a DNA strand called?
Each end of DNA molecule has a number. One end is referred to as 5' (five prime) and the other end is referred to as 3' (three prime). The 5' and 3' designations refer to the number of carbon atom in a deoxyribose sugar molecule to which a phosphate group bonds.
Why do eukaryotic chromosomes have telomeres?
Telomeres are the physical ends of eukaryotic chromosomes. They protect chromosome ends from DNA degradation, recombination, and DNA end fusions, and they are important for nuclear architecture. Telomeres provide a mechanism for their replication by semiconservative DNA replication and length maintenance by telomerase.
What does each eukaryotic chromosome contain?
Each eukaryotic chromosome is composed of DNA coiled and condensed around nuclear proteins called histones. Humans inherit one set of chromosomes from their mother and a second set from their father.
Do eukaryotic chromosomes have histones?
In eukaryotic cells, chromatin consists of all the DNA within the nucleus and its associated proteins, called histones. Eukaryotic chromosomes are composed of chromatin, and each consists of two complementary strands of DNA coiled tightly around histones.
What are the components of eukaryotic chromosomes quizlet?
a beadlike structure of eukaryotic chromosomes, consisting of a core of eight histone molecules wrapped by a DNA segment about 150 base pairs in length and separated by "linker" DNA.
What happens at end of meiosis1?
Meiosis I ends when the chromosomes of each homologous pair arrive at opposing poles of the cell. The microtubules disintegrate, and a new nuclear membrane forms around each haploid set of chromosomes. The chromosomes uncoil, forming chromatin again, and cytokinesis occurs, forming two non-identical daughter cells.
What does a chromosome consist of?
A chromosome is made up of proteins and DNA organized into genes. Each cell normally contains 23 pairs of chromosomes.
What is on a chromosome?
Chromosomes are thread-like structures located inside the nucleus of animal and plant cells. Each chromosome is made of protein and a single molecule of deoxyribonucleic acid (DNA). Passed from parents to offspring, DNA contains the specific instructions that make each type of living creature unique.
What 2 main things make up a chromosome?
DNA and histone proteins are packaged into structures called chromosomes.
What is the structure of chromosome ends?
Throughout the eukaryotic kingdom, the overall structure of chromosome ends is conserved and is characterized by the telomeric tract - a series of short G-rich repeats. This is succeeded by an extensive subtelomeric region consisting of various types and lengths of repeats - the telomere associated sequences (TAS).
What sequences are required for a properly functioning chromosome?
Some sequences are required for a properly functioning chromosome: Centromere: Used during cell division as the attachment point for the spindle fibers. Telomere: Used to maintain chromosomal integrity by capping off the ends of the linear chromosomes. This region is a microsatellite, but its function is more specific than a simple tandem repeat.
What are retrotransposons in DNA?
Retrotransposons are sequences in the DNA that are the result of retrotransposition of RNA. LINEs and SINEs are examples where the sequences are repeats, but there are non-repeated sequences that can also be retrotransposons.
What is the function of an intron?
Its function, if any, is unknown. Introns are intervening sequences between the exons that are never translated. Some sequences inside introns function as miRNA, and there are even some cases of small genes residing completely within the intron of a large gene.
What is the coding region of mRNA?
The exons can be divided into three parts. The coding region is the portion of the mRNA that will eventually be translated. Upstream untranslated region ( 5' UTR) can serve several functions, including mRNA transport, and initiation of translation (including, portions of the Kozak sequence ).
What are the promoter regions of transcription?
Promoter regions (normally less than a couple of hundred basepairs upstream of transcription) include elements such as the TATA and CAAT boxes, GC elements, and an initiator. Exons are the part of the transcript that will eventually be transported to the cytoplasm for translation.
Do eukaryotic chromosomes contain DNA?
Typical eukaryotic chromosomes contain much more DNA than is classified in the categories above. The DNA may be used as spacing, or have other as-yet-unknown function. Or, they may simply be random sequences of no consequence.
Where are loops of chromatin located in mitotic chromosomes?
B. Electron micrographs of whole-mounted mitotic chromosomes show loops of chromatin at the periphery of the chromosomes.
What is the function of centromeres?
One of the functions of a centromere is to contribute to proper chromosome segregation. The other function is to
How do telomeres function?
Telomeres appear to function in at least two ways during the replication of chromosomes. One way is to provide a primer for DNA polymerase. The second is to
What is DNA winding around?
A. DNA winding around histones to form small nucleosomes.
Can a strand begin at the 5' end?
A. It cannot begin the 5' end of a new strand without a primer.
Is DNA protected inside a nucleosome?
A. DNA is not protected inside a nucleosome.
Do telomeres shorten with cell division?
A. Telomeres shorten slightly with each cell division.
Overview
Eukaryotic chromosome fine structure refers to the structure of sequences for eukaryotic chromosomes. Some fine sequences are included in more than one class, so the classification listed is not intended to be completely separate.
Chromosomal characteristics
Some sequences are required for a properly functioning chromosome:
• Centromere: Used during cell division as the attachment point for the spindle fibers.
• Telomere: Used to maintain chromosomal integrity by capping off the ends of the linear chromosomes. This region is a microsatellite, but its function is more specific than a simple tandem repeat.
Structural sequences
Other sequences are used in replication or during interphase with the physical structure of the chromosome.
• Ori, or Origin: Origins of replication.
• MAR: Matrix attachment regions, where the DNA attaches to the nuclear matrix.
Protein-coding genes
Regions of the genome with protein-coding genes include several elements:
• Enhancer regions (normally up to a few thousand basepairs upstream of transcription).
• Promoter regions (normally less than a couple of hundred basepairs upstream of transcription) include elements such as the TATA and CAAT boxes, GC elements, and an initiator.
Genes that are used as RNA
Many regions of the DNA are transcribed with RNA as the functional form:
• rRNA: Ribosomal RNA are used in the ribosome.
• tRNA: Transfer RNA are used in the translation process by bringing amino acids to the ribosome.
• snRNA: Small nuclear RNA are used in spliceosomes to help the processing of pre-mRNA.
Repeated sequences
Repeated sequences are of two basic types: unique sequences that are repeated in one area; and repeated sequences that are interspersed throughout the genome.
Satellites are unique sequences that are repeated in tandem in one area. Depending on the length of the repeat, they are classified as either:
• Minisatellite: Short repeats of nucleotides.
Retrotransposons
Retrotransposons are sequences in the DNA that are the result of retrotransposition of RNA. LINEs and SINEs are examples where the sequences are repeats, but there are non-repeated sequences that can also be retrotransposons.
Other sequences
Typical eukaryotic chromosomes contain much more DNA than is classified in the categories above. The DNA may be used as spacing, or have other as-yet-unknown function. Or, they may simply be random sequences of no consequence.