Genetic organelles

• The nucleus contains most of the DNA in a eukaryotic cell
• The eukaryotic cell's genetic instructions are housed in the nucleus and carried out by the ribosomes.
• Ribosomes use the information from the DNA to make proteins.
• The nucleus contains most of the cell's genes and is usually the most conspicuous organelle.
• The nuclear envelope encloses the nucleus, separating it from the cytoplasm.
• The nuclear membrane is a double membrane; each membrane contains a lipid bilayer - the inner nuclear membrane and the outer nuclear membrane.
• The nucleolus is a prominent structure in the nucleus and the site of ribosomal RNA (rRNA) synthesis and the synthesis of ribosomes.
• Nuclear pores regulate the entry and exit of molecules to pass between the nucleus and cytoplasm.
• The shape of the nucleus is maintains by the nuclear lamina, which is composed of proteins.
• Nucleoplasm is the semi-fluid matrix within the nucleus where various components, including the nucleolus, are suspended. It provides the physical environment for the nucleolus to carry out its functions.
• In the nucleus, DNA is organized into discrete units called chromosomes.
• Each chromosomes is composed of a single DNA molecule associated with proteins.
• The DNA and proteins of chromosomes are together called chromatin.
• Chromatin condenses to form discrete chromosomes as a cell prepares to divide.
• Ribosomes are the particles made of ribosomal RNA and protein.
• Some ribosomes are free ribosomes; others are bound.
• Free ribosomes are suspended in the cytoplasm and typically involved in making proteins that function in the cytoplasm.
• Bound ribosomes are attached to the endoplasmic reticulum (ER) associated with the nuclear envelope and associated with proteins packed in certain organelles or exported from the cell.
• DNA/Genes/Chromosomes/Chromatin/Chromatid

  
  

  Genes - group/s of DNA
• Prokaryotic Cell

  Plasmid - extra copy of chromosomes
• DNA can also be found in the mitochondria and the chloroplast.

  • Mitochondrial DNA (mtDNA) is separate from nuclear DNA and is inherited maternally.
  • Chloroplast DNA (cpDNA) is distinct from nuclear DNA and is maternally inherited in most plants.
• mRNA - messenger

  tRNA - transfer

  rRNA - ribosomal
• Location and types:

  Ribosomes

  • cytoplasm - free ribosomes
  • rough endoplasmic reticulum - attached or bound ribosomes
• Central dogma of biology


  Describes the flow of genetic information within a biological system, primarily focusing on how genetic information is transferred from DNA to RNA to protein
• DNA Replication


  • DNA makes an exact copy of itself
  • During replication, the double-stranded DNA molecule unwinds
  • Each strand serves as a template for synthesis of a new complementary strand
  • Results in two identical DNA molecules
• Transcription

  • DNA is copied into a complementary RNA molecule.
  • RNA polymerase enzyme binds to a specific region of DNA called the promoter and synthesizes a single-stranded RNA molecule using one of the DNA strands as a template.
  • RNA molecule produced is messenger RNA (mRNA)
• Translation

  • Information carried by mRNA is decoded to synthesize a specific protein.
  • Occurs in ribosomes.
  • Transfer RNA (tRNA) molecules bring amino acids to the ribosome according to the codons (three-nucleotide sequences) on the mRNA.
  • The amino acids are then joined together in a specific order dictated by the mRNA sequence to form a polypeptide chain.
  • The polypeptide chain folds into a functional protein.
• Four nitrogenous bases that make up the genetic code:

  • A - adenine
  • T - thymine
  • C - cytosine
  • G - guanine

  These nitrogenous bases are the building blocks of DNA and form the sequence of nucleotides along the DNA molecule. The specific sequence of these bases encodes genetic information, which determines the characteristics and functions of an organism.
• DNA, a double-stranded molecule, is tightly coiled in an organized structure called chromosomes.
• A chromosome is simply a long, continuous thread of DNA wounded together by DNA-associated proteins, referred as histones.
• Each of your body cells consists of 46 chromosomes or 23 pairs. If stretched end to end, it will be about 10 feet long.
• Chromosomes must condense first, before they divide into two daughter cells.
• During cell division, the chromosomes become tightly condensed so they will not be entangled during cell division.
• Before the onset of cell division, DNA is loosely organized like a scattered spaghetti on a plate.
• Chromatin is a complex set of macromolecules that contain loose DNA, proteins, and RNA.
• Chromatin is responsible for packaging the DNA efficiently into smaller volume so that it fits the nucleus of a cell to protect the DNA structure and sequence and to reinforce the DNA molecule to allow mitosis and meiosis.
• Chromatid refers to each strand of the duplicated chromosomes. Together they are called sister chromatids.
• Sister chromatids are held together by centromere, a region of condensed pinched chromosomes.
• Once the chromosome has been copied, the chromosome now appears to be similar to a letter X in which the left and the right halves are identical.
• Located at the centromere is a group of proteins called kinetochore, which is attached to the long spindle fibers during cell division.