Nucleus structure and function

Nuclear Membrane Definition The nuclear membrane, also called the nuclear envelope, is a double membrane layer that separates the contents of the nucleus from the rest of the cell. It is found in both animal and plant cells. A cell has many jobs, such as building proteins, converting molecules into energy, and removing waste products. The nuclear envelope protects the cell’s genetic material from the chemical reactions that take place outside the nucleus. It also contains many proteins that are used in organizing DNA and regulating genes. Function of the Nuclear Membrane The nuclear membrane is a barrier that physically protects the cell’s DNA from the chemical reactions that are occurring elsewhere in the cell. If molecules that stay in the cytoplasm were to enter the nucleus, they could destroy part of the cell’s DNA, which would stop it from functioning properly and could even lead to cell death. The envelope also contains a network of proteins that keep the genetic material in place inside the nucleus. It also manages what materials can enter and exit the nucleus. It does so by being selectively permeable. Only certain proteins can physically pass through the double layer. This protects genetic information from mixing with other parts of the cell, and allows different cellular activities to occur inside the nucleus and outside the nucleus in the cytoplasm, where all other cellular structures are located. Parts of the Nuclear Membrane The nuclear membrane surrounds the ...

Cell Nucleus Definition The cell nucleus is a large organelle in eukaryotic organisms which protects the majority of the DNA within each cell. The nucleus also produces the necessary precursors for protein synthesis. The DNA housed within the cell nucleus contains the information necessary for the creation of the majority of the proteins needed to keep a cell functional. While some DNA is stored in other organelles, such as mitochondria, the majority of an organism’s DNA is located in the cell nucleus. The DNA housed in the cell nucleus is extremely valuable, and as such the cell nucleus has a variety of important structures to help maintain, process, and protect the DNA. Cell Nucleus Structure A cell nucleus is surrounded by a double membrane, known as the nuclear envelope. This membrane covers and protects the DNA from physical and chemical damage. In doing so, the membrane creates a separate environment to process the DNA in. The outer membrane is in contact with the cytoplasm, and connects in some places to the endoplasmic reticulum. The inner membrane connects to the nuclear lamina. This nuclear framework inside the cell nucleus helps it maintain its shape. There is also evidence that this scaffolding of proteins helps form a matrix to transport and distribute products within and out of the nucleus. Nuclear pores create passages through the nuclear membrane, and allow products of the cell nucleus to enter the cytoplasm or endoplasmic reticulum. The pores also allow so...

Portions containing DNA alone alternate with sections containing DNA wrapped around the histones. The histone components actually consist of octets, or groups of eight. These eight subunits come in four pairs. Where the DNA meets these histone octets, it wraps itself around the histones like thread being wound around a spool. At the start of transcription, the DNA double helix in the region to be transcribed becomes partially unwound, resulting in a transcription bubble. At this point, enzymes and other proteins that contribute to transcription have migrated to the region. Some of these bind to a DNA sequence of nucleotides called a promoter. • Each three-nucleotide combination (AAA, AAC, etc.) carries the code for a distinctamino acid. The 20amino acidsfound in the human body are what make up proteins. • Since there are 64 possible combinations of three bases from among a total of four (4 raised to the power of 3), someamino acidshave multiple codons, as they are called, associated with them. But_each codon invariably codes for the sameamino acid_. • Transcription errors do occur in nature, leading to mutated or incomplete protein products down the line, but overall such errors are statistically rare, and their overall impact is thankfully limited. At the start of mitosis, the chromosomes, which to this point in the cell's life cycle have sat rather loosely in the nucleus, become far more condensed, while the nucleolus does the opposite and becomes harder to visualize; du...