5 Flashcards
What are the three main components of a nucleotide?
- A pentose sugar
- A phosphate group
- Nitrogenous base
What is complementary base pairing in DNA?
In DNA, adenine (A) pairs with thymine (T) via two hydrogen bonds - and guanine (G) pairs with cytosine (C) via three hydrogen bonds
What type of bond holds the two strands of DNA together?
Hydrogen bonds between complementary nitrogenous bases
What is the significance of DNA being antiparallel?
The two DNA strands run in opposite directions, meaning one strand runs 5’ to 3’ and the complementary strand runs 3’ to 5’
What is the sugar-phosphate backbone in DNA?
The sugar-phosphate backbone is the repeating structure of sugar (deoxyribose) and phosphate that forms the outer structure of DNA, with the nitrogenous bases pointing inward
What is a chromosome?
a long strand of DNA tightly packed with proteins, mainly histones, that carry genetic information
What is chromatin?
Chromatin is the material that makes up chromosomes, consisting of DNA and histone proteins
What is the role of histones in DNA packaging?
Histones are proteins around which DNA wraps to form nucleosomes, the basic units of chromatin structure, aiding in DNA condensation and accessibility
What is a nucleosome?
A nucleosome is a structural unit of chromatin, consisting of DNA wrapped around a core of eight histone proteins
How do histones and DNA interact?
DNA, which is negatively charged due to its phosphate groups, wraps around positively charged histones, which contain basic amino acids like lysine and arginine
What is the first level of DNA packaging in eukaryotic chromosomes?
DNA wraps around histone proteins to form nucleosomes, which are the first level of packaging
What is the 30 nm fiber in chromosome structure?
The 30 nm fiber is a further condensed form of chromatin, where nucleosomes are packed together with the help of histone H1
How is chromatin made dynamic to allow replication and transcription?
Chromatin is made dynamic through chromatin remodeling complexes and histone modifications, such as acetylation, which loosen or tighten the chromatin structure
What is the role of histone acetylation?
Acetylation of histone tails neutralizes the positive charge, loosening the interaction between histones and DNA, thus making the chromatin more accessible for transcription
What are the key structural components of a eukaryotic chromosome that ensure its replication and separation?
The telomere (protects the ends of chromosomes and allows for complete replication), the replication origin (where replication begins), and the centromere (attaches to mitotic spindles during cell division)
What is the function of the nuclear membrane?
The nuclear membrane (or nuclear envelope) consists of two concentric membranes that separate the nucleus from the cytoplasm and contains nuclear pores for selective transport
What is the function of the nucleolus?
The nucleolus is the site of ribosomal RNA (rRNA) synthesis and the assembly of ribosomal subunits
What is the difference between interphase and M-phase chromosomes?
Interphase chromosomes are less condensed and allow for gene expression and replication, while M-phase chromosomes are highly condensed to facilitate segregation during cell division
What is the genome?
The genome is the complete set of genetic information in an organism’s DNA
What causes the uniform diameter of the DNA double helix?
The pairing of purines (adenine and guanine) with pyrimidines (thymine and cytosine) ensures a uniform diameter, with A pairing with T and G pairing with C
What role do nuclear pores play in the cell?
Nuclear pores act as selective channels that regulate the movement of molecules, such as RNA and proteins, between the nucleus and the cytoplasm
How long is the total length of DNA in a single human cell?
Approximately 2 meters of DNA are packed into each human cell
What is the challenge related to packaging DNA into chromosomes?
The challenge is to compact the 2 meters of DNA into a nucleus that is only about 5 µm in diameter, while still maintaining accessibility for replication and transcription
How do chromatin remodeling complexes affect DNA packaging?
Chromatin remodeling complexes reposition or restructure nucleosomes to allow greater accessibility to DNA, facilitating processes like replication and transcription
What is the significance of telomeres on chromosomes?
Telomeres protect the ends of chromosomes from degradation and ensure that the entire length of the chromosome is replicated
What is the role of centromeres during cell division?
Centromeres are DNA sequences that allow chromosomes to attach to mitotic spindles during cell division, ensuring proper chromosome segregation
What is chromatin made of?
Chromatin consists of DNA and proteins, primarily histones, which help in the compaction and organization of DNA within the nucleus
What happens during histone deacetylation?
Histone deacetylation removes acetyl groups from histones, restoring their positive charge, which leads to tighter chromatin packing and inhibits transcription
Why do purines always pair with pyrimidines in DNA?
Purines (adenine and guanine) are larger, two-ring structures, while pyrimidines (thymine and cytosine) are smaller, single-ring structures. Pairing them maintains the uniform diameter of the DNA double helix
Why is DNA packaging dynamic, and why is this important for the cell?
DNA packaging must be dynamic to allow for gene expression, replication, and repair, which require access to specific regions of the DNA at different times
What is the function of histone H1?
Histone H1 helps pull nucleosomes together, forming a more condensed 30 nm fiber, which is an important step in chromatin packaging
How many histone proteins make up the core of a nucleosome?
The nucleosome core consists of 8 histone proteins (2 copies each of H2A, H2B, H3, and H4)
What happens to chromosomes during the M-phase of the cell cycle?
Chromosomes become highly condensed to ensure accurate segregation during mitosis
