DNA

• deoxyribonucleic acid (DNA) is a biomolecule that has an essential role on how our cells produce proteins
• DNA is made up of chains of nucleotides. Each nucleotide consists of a five-carbon sugar called deoxyribose (deoxy– means “without oxygen") and a sugar-phosphate backbone group, which make up the nitrogenous bases of DNA.
• There are four nitrogenous bases found in DNA. They are cytosine (C), guanine (G), adenine (A), and thymine (T).
• Adenine and guanine are considered purines because their structure has two rings.
• cytosine and thymine are pyrimidines because their structure only has one ring.
• DNA is described as a double helix, whose structure is similar to a twisted ladder. The five-carbon sugar and the phosphate group form the handles of the ladder, and the nitrogenous base pairs create the steps of the ladder.
• Replication is the process wherein DNA produces new copies of itself. This process is described as semiconservative because, after DNA replication, the new copies contain both the old strand and the new strand
• Steps in DNA Replication:

  1. Fork Transformation – unbinding
  2. Primer Binding – template
  3. Elongation – creating new bonds
  4. Termination – proofreading
• Terms to Remember in DNA Replication:

  • DNA Helicase – separates DNA strands
  • Primase – generates RNA primers
  • Primers – template for starting point of

  replication

  • Polymerases – adds nucleotides to leading

  and lagging strands

  • Topoisomerase – prevents DNA from being

  tangled

  • DNA Ligase – joins Okazaki fragments
  • Okazaki fragments – pieces of newly

  created DNA

  • Lagging strand – 3’-5’ (discontinuous)

  Leading strand – 5’-3’ (continuous)

  Single strand binding proteins – holds the

  opened strand
• RNA is single-stranded and is made up of a phosphate group and a five-carbon sugar called ribose. It is also made of nitrogenous bases: cytosine, guanine, adenine, and uracil (U).
• there are three main types of RNA:

  • Messenger RNA (mRNA) – acts as a “messenger” that copies the nucleotide sequence of the DNA inside the nucleus and carries it out to the cytoplasm

  • Ribosomal RNA (rRNA) – is the site where the proteins are assembled

  • Transfer RNA (tRNA) – carries amino acids and transfers them to the ribosome
• transcription happens when the mRNA enters the nucleus and copies the nucleotide sequence of DNA
• Steps in DNA Transcription:

  1.Initiation – RNA polymerase connects to section of DNA where promoter is located

  2. Elongation – Polymerase separates strands to make space

  3. Termination – polymerase separate from strands and mRNA leaves nucleus to go to cytoplasm

  • Terminator: signals completion of mRNA
• translation happens when the nucleotide sequence carried by the mRNA will be used in this process. It begins once mRNA attaches to a ribosome.
• Steps in DNA Transcription:

  1. mRNA attaches to Ribosome
  2. tRNA carries anticodon and 3 nitrogenous bases. mRNA joins tRNA in ribosome

  Stop Codon – UGA UAG UAA
• Translation sites:

  • Pepridyl tRNA (P site) – location of growing chain of polypeptide
  • Aminocyl tRNA (A site) – carries next amino acid
  • Exit (E site) – holding place for discharged tRNA
• any incorrect pairing of bases may lead to mutation.
• two types of mutation: gene mutation and chromosomal mutation
• gene is a sequence of DNA that determines a trait
• chromosome, which can be found inside the nucleus, contains the genes, which are transmitted from one generation to another, especially during cell reproduction
• Gene Mutation

  • errors in the DNA replication
  • alternation occurs in the nucleotide sequence
  • single gene
• Chromosomal Mutation

  • Errors in crossing over meiosis
  • Alternation occurs in segment
  • several genes are affected
• Chromosomal Mutation Types: Deletion, Duplication, Inversion, Translocation, Nondisjuntion
• Chromosomal Mutation Type:

  Deletion is when a part of a chromosome is deleted, making it shorter than its normal size.
• Chromosomal Mutation Type:

  Duplication is when a part of a chromosome became longer due to an extra segment attached to it
• Chromosomal Mutation Type:

  Inversion is when a part of a chromosome is attached in reverse orientation.
• Chromosomal Mutation Type:

  Translocation is when a part of two chromosomes interchange
• Chromosomal Mutation Type:

  Nondisjunction The chromosomes that make up a pair fail to separate during meiosis, resulting in an unequal number of chromosomes in the cell
• Gene Mutation Type:

  Point mutation or substitution happens when there is a replacement of a nucleotide. It affects a gamete or a sex cell (sperm or egg), causing a disorder that can be transmitted to the next generation
• Gene Mutation Type:

  Missense mutation happens when there is a substitution in the amino acid of a protein
• Gene Mutation Type:

  Nonsense mutation is when a stop codon was added to prevent the effect of a substitution in the production of proteins
• Gene Mutation Type:

  Frameshift happens when one or a few nucleotide pairs in the DNA are deleted or inserted.
• karyotyping is a process wherein the chromosomes of an organism are arranged by pairs, according to size and structure.
• Types of mutation:

  • Somatic – in body cells which means it’s not passed on
  • Germline – in reproductive cells which means it is passed on
• Mutagens: Physical, Chemical, Biological
• Down Syndrome

  Description: Person with mild to severe mental retardation, highly vulnerable to other diseases, and born with birth defects

  Mutational Cause:Trisomy 21 (a chromosomal mutation wherein there is an extra chromosome 21)
• Turner Syndrome

  Description: A sterile person with sex organs that do not develop

  Mutational Cause: Lack of a sex chromosome, wherein the person’s genotype is XO (O stands for the missing gene)
• Klinefelter Syndrome

  Description: An affected person with abnormal body structure (e.g., enlarged breasts, small penis)

  Mutational Cause: Contains an extra X chromosome (XXY), which makes the person have 47 chromosomes instead of the normal 46
• Progeria

  Description:Development of adultlike appearance and features associated with older people to children

  Mutational Cause:

  Point mutation in a single gene called lamin A (lamin is a family of proteins)
• Timeline of the discover of DNA

  A) Frederick Griffith

  B) Oswald Avery

  C) Erwin Chargaff

  D) Alfred Hershey

  E) Martha Chase

  F) Rosalind Franklin

  G) Maurice Wilkins

  H) Francis Crick

  I) James Watson