Packaging of dna helix

DNA Packaging The DNA structure was proposed by Watson and Crick. According to them, the DNA is a double-helical structure with two polynucleotide strands running anti-parallel to each other. This double helix is negatively charged due to the presence of phosphate groups in the DNA backbone. The cell makes histone proteins that bind the DNA to counterbalance the negative charge. These histone proteins are involved in DNA packaging. Read on to explore what is DNA packaging and why it is required. Table of Contents • • • • What is DNA Packaging? Have you ever wondered how DNA is present in a nucleus smaller than it? This can be explained by the process of DNA packaging. DNA is an organic, complex, molecular structure found in both prokaryotic and eukaryotic cells and also in many viruses. It is a hereditary material which is found in the nucleus of the cell and is mainly involved in carrying genetic information. The DNA structure has the following characteristics: • The strands of the DNA are helically wounded, every single strand forms a right-handed coil. • The pitch of each helix is 3.32 nm, and about 10 nucleotides make up one turn. • The distance between two succeeding base pairs is 0.34 nm • The total length of a DNA is the distance between two succeeding base pairs and the product of a total number of base pairs. • A typical DNA strand has a length of approximately 2.2 meters, which is much longer than a nucleus. Prokaryotic cells can be distinguished from All eukar...

\( \newcommand\) • • • • • • • • Search Fundamentals of Biochemistry Some of the material in this chapter section comes from Chapter 8.4, Chromosomes and Chromatin, as it was important to describe it earlier in the structure/function unit. In addition, some biochemistry courses might not get to the material in a late chapter in a text. Repetition of some of the material is easier in an online textbook as well. Introduction Recall from Chapter 8, that within eukaryotic cells, DNA is organized into long linear structures called chromosomes, as shown in Figure \(\PageIndex\): Diagram of Replicated and Condensed Eukaryotic Chromosome. (1) Chromatid – one of the two identical parts of the chromosome after the S phase. (2) Centromere – the point where the two chromatids are joined together. (3) Short arm is termed p; the Long arm is termed q. Image by: Eukaryotic organisms (animals, plants, fungi, and protists) store most of their DNA inside the cell nucleus as linear nuclear DNA, and some in the mitochondria as circular mitochondrial DNA or in chloroplasts as circular chloroplast DNA. In contrast, prokaryotes (bacteria and archaea) do not have organelle structures and thus, store their DNA only in a region of the cytoplasm known as the nucleoid region. Prokaryotic chromosomes consist of double–stranded circular DNA. The genome of a cell is often significantly larger than the cell itself. For example, if the DNA from a human cell containing 46 chromosomes were stretched out in a...

Most students learn at an early age that organisms can be broadly divided into two types: prokaryotes and eukaryotes. In primary school, children are taught that the main difference between these organisms is that eukaryotic cells contain membrane-bound organelles, such as the nucleus, while prokaryotic cells do not. There is much more to the story, however, particularly with regard to chromosomal structure and organization. Much of what is known about prokaryotic chromosome structure was derived from studies of Escherichia coli, a bacterium that lives in the human colon and is commonly used in laboratory cloning experiments. In the 1950s and 1960s, this bacterium became the model organism of choice for prokaryotic research when a group of scientists used phase-contrast microscopy and autoradiography to show that the essential genes of E. coli are encoded on a single circular chromosome packaged within the cell nucleoid (Mason & Powelson, 1956; Cairns, 1963). Prokaryotic cells do not contain nuclei or other membrane-bound organelles. In fact, the word " prokaryote" literally means "before the nucleus." The nucleoid is simply the area of a prokaryotic cell in which the chromosomal DNA is located. This arrangement is not as simple as it sounds, however, especially considering that the E. coli chromosome is several orders of magnitude larger than the cell itself. So, if bacterial chromosomes are so huge, how can they fit comfortably inside a cell—much less in one small corner...

This animation shows how DNA molecules are packed up into chromosomes. DNA is tightly packed up to fit in the nucleus of every cell. As shown in the animation, a DNA molecule wraps around histone proteins to form tight loops called nucleosomes. These nucleosomes coil and stack together to form fibers called chromatin. Chromatin, in turn, loops and folds with the help of additional proteins to form chromosomes. Condensing DNA into chromosomes prevents DNA tangling and damage during cell division. Depending on students’ background, it may be helpful to pause the animation at various points to discuss different structures.

You may have had a relative say to you, “You look exactly like your father” or “You have the same eyes as your mother!” Have you ever wondered what is the reason for this? It is because of your DNA! You get 50% of your DNA from your father and the other 50% from your mother. Want to learn more about the components and structure of this interesting molecule? Let’s dive in. Structure of DNA The genetic material in most organisms is DNA or Deoxyribonucleic acid; whereas in some viruses, it is RNA or Ribonucleic acid. A DNA molecule consists of two polynucleotide chains i.e. chains with multiple nucleotides. Let’s understand the structure of this chain in detail. Structure Of Polynucleotide Chain A nucleotide is made of the following components: • Pentose sugar – A pentose sugar is a 5-carbon sugar. In case of DNA, this sugar is deoxyribose whereas, in RNA, it is ribose. • Phosphate group • Nitrogenous base – These can be of two types – Purines and Pyrimidines. Purines include Adenine and Guanine whereas pyrimidines include Cytosine and Thymine. In RNA, thymine is replaced by Uracil. Nitrogenous base + pentose sugar (via N-glycosidic linkage) = Nucleoside. Nucleoside + phosphate group (via phosphoester linkage) = Nucleotide. Nucleotide + Nucleotide (via 3′-5′ phosphodiester linkage) = Dinucleotide. Many nucleotides linked together = Polynucleotide. A polynucleotide has a free phosphate group at the 5′ end of the sugar and this is called the 5′ end. Similarly, the sugar also ha...

What you’ll learn to do: Understand chromosome structure and organization in eukaryotic cells When a cell divides, it is essential that the new cell (also known as the daughter cell) contains the same genetic information as the old cell (also known as the parent cell). This genetic information is our DNA, which is packaged into chromosomes. Each chromosome contains information about specific traits of an organism. These chromosomes can be sorted into two categories: autosomes and sex chromosomes. In this section will discuss these two types of chromosomes and the differences between the two as well as how cells package DNA. Watch the video below for an overview of chromosomes. DNA and Chromosomes When a cell divides in two, one of its main jobs is to make sure that each of the two new cells gets a full, perfect copy of genetic material. Mistakes during copying, or unequal division of the genetic material between cells, can lead to cells that are unhealthy or nonfunctional (and even to diseases such as cancer). But what exactly is this genetic material, and how does it behave over the course of a cell division? DNA and Genomes DNA (deoxyribonucleic acid) is the genetic material of living organisms. In humans, DNA is found in almost all the cells of the body and provides the instructions they need to grow, function, and respond to their environment. When a cell of the body divides, it will pass on a copy of its DNA to each of its daughter cells. DNA is also passed on at the ...

Learning Outcomes • Explain how DNA packaging in both eukaryotic and prokaryotic cells protects genetic information When comparing prokaryotic cells to eukaryotic cells, prokaryotes are much simpler than eukaryotes in many of their features (Figure 1). Most prokaryotes contain a single, circular chromosome that is found in an area of the cytoplasm called the nucleoid. Figure 1. A eukaryote contains a well-defined nucleus, whereas in prokaryotes, the chromosome lies in the cytoplasm in an area called the nucleoid. In eukaryotic cells, DNA and RNA synthesis occur in a separate compartment from protein synthesis. In prokaryotic cells, both processes occur together. What advantages might there be to separating the processes? What advantages might there be to having them occur together? Compartmentalization enables a eukaryotic cell to divide processes into discrete steps so it can build more complex protein and RNA products. But there is an advantage to having a single compartment as well: RNA and protein synthesis occurs much more quickly in a prokaryotic cell. The size of the genome in one of the most well-studied prokaryotes, E.coli, is 4.6 million base pairs (approximately 1.1 mm, if cut and stretched out). So how does this fit inside a small bacterial cell? The DNA is twisted by what is known as supercoiling. Supercoiling means that DNA is either under-wound (less than one turn of the helix per 10 base pairs) or over-wound (more than 1 turn per 10 base pairs) from its nor...