Exam 1 Review:  Chapter 3 - The Nucleus

nucleus - The large, membrane-bound, usually oval or spherical organelle within the cytoplasm of (almost all) living cells, containing the cell's hereditary material (DNA in the form of chromosomes) and controlling the cell's metabolism, growth, and reproduction.

genes - The units of hereditary, consisting of a sequence of DNA that occupies a specific location on a chromosome and determines a particular characteristic in an organism; at the molecular level, genes specify the primary structure of the proteins which make up the organism; DNA and its genes are found in the nucleus and in the mitochondria; genes are duplicated and transmitted during the process of cell division; genes undergo mutation when their DNA sequence changes

chromosomes - The dark-staining rod-like structures seen when DNA is maximally supercoiled during the processes of nuclear division termed mitosis and meiosis.  Humans have 23 pairs of chromosomes.

chromatin - The form and appearance of DNA during interphase in the cell nucleus; it consists of a complex of nucleic acids and proteins, primarily histones, which provide for the first level of DNA supercoiling; since the DNA is not fully supercoiled in this configuration, it stains lightly with basic dyes to give an indistinct granular appearance; it condenses to form the fully supercoiled chromosomes during cell division.

histone proteins - Any of several small, basic = alkaline (containing a high proportion of basic amino acids) proteins most commonly found in association with the DNA in the chromatin; they provide the framework for the first level of DNA supercoiling, the nucleosome configuration; they also play a role in genetic regulation.

DNA supercoiling - The general term representing the series of sequential packaging mechanisms which permit the exceedingly long DNA molecules to be housed within the nucleus in an orderly arrangement so that particular sequences, genes, can be accessed efficiently when needed.

messenger RNA - The diverse class of RNA molecules which mediate the transfer of genetic information ("protein blueprints") from the DNA in the cell nucleus to the ribosomes in the cytoplasm, where they serves as templates for protein synthesis during the process of translation; it is synthesized from a DNA template during the process of transcription in the nucleus.  aka - mRNA.

DNA base complimentarity - The term which describes the consistent hydrogen bonding between nitrogenous bases in DNA and RNA; example: adenine always pairs with thymine (DNA) or uracil (RNA) with two hydrogen bonds and guanine always pairs with cytosine with three hydrogen bonds.

nuclear envelope = nuclear membrane - The double-layered membrane enclosing the nucleus of a cell and separating it from the cytoplasm; it is often continuous at some points with the endoplasmic reticulum; it contains many large pores and typically has some ribosomes attached to its cytoplasmic surface.

nuclear pores - Large (but still only visible with the electron microscope) protein complexes which span the width of the nuclear envelope = nuclear membrane and serve as channels through which a variety of water soluble solutes, including relatively large proteins and nucleic acids may pass; a typical nucleus has ~3,000 of them.

nucleolus - The small, typically round, non-membrane-bound granular bodies (organelles) composed of protein and RNA and located in the nucleus of most cells during interphase; they are usually associated with a specific chromosomal site which is the location for the genes for rRNA; it is involved in ribosomal RNA synthesis and the formation of ribosomes.

transcription - The first major process in protein synthesis, where genetic information from a nuclear gene is copied to form a messenger RNA blueprint which codes for the amino acid sequence in the polypeptide chain; the mRNA must migrate to the cytoplasm to the ribosome to participate in translation.

translation - The second major process in protein synthesis, where genetic information from a nuclear gene is actually transformed into a polypeptide chain at the ribosome.

codon - The sequence of three nucleotides ("triplet") on each mRNA = messenger RNA molecule, in a linear order specified by the DNA blueprint, which hydrogen bonds in a complementary fashion to the triplet anticodon sequence of a tRNA = transfer RNA molecule; this specific binding ensures that the correct amino acid will be joined by a peptide bond to the growing chain of the polypeptide being synthesized by the ribosome.

codon dictionary - The set of 64 combinations of nitrogenous bases found in mRNA which are complimentary to the DNA triplets which represent the 20 amino acids which can be assembled into polypeptides; since there are more codons than amino acids, one amino acid may be represented by more than one codon triplet; however, each triplet represents one and only one amino acid; one of the triplets represents "start" synthesis signal and three of the triplets represent "stop" synthesis signals.

anticodon - The sequence of three nucleotides ("triplet") in a special location on each tRNA = transfer RNA molecule which hydrogen bonds in a complementary fashion to the triplet codon sequence of a mRNA = messenger RNA molecule; this specific binding ensures that the correct amino acid will be joined by a peptide bond to the growing chain of the polypeptide being synthesized by the ribosome.

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