4 - CENTRAL DOGMA Flashcards
- Proposed by Watson and Crick in 1950
- Described the relationship between nucleic acid and proteins as a directional flow of information
- Deals with the detailed residue-by-residue transfer of sequential information
Central Dogma
3 important steps of the central dogma
- Transcription
- Translation
- DNA Replication
Monomer units or building blocks of nucleic acids
Nucleotides
Components of nucleotides
Sugar + nitrogenous base + phosphate group
Functions of nucleotides
- Part of the coenzymes
- Serves as donors of the phosphoric group (ATP, GTP), of sugars (UDP or GDP sugars), or of lipids
- Regulatory second messengers
- Chemotherapy and immune suppression
- Nitrogen-containing heterocycles
- Cyclic compounds whose rings contain both carbon and other elements
- These are information-containing parts of the DNA because they form sequences
Nitrogenous Base
thousand base pairs
Kilobase
million base pairs
Megabase
- 6-membered ring containing 2 nitrogens
- Cytosine, Uracil, Thymine
Pyrimidines (CUT)
- 9-membered ring consisting of 4 nitrogens
- Adenine, Guanine
Purines (AG)
- Pairing of the single ring pyrimidine with the double-ring purine
- Ensures the symmetrical double helix formation of the DNA
Complementary Base Pairs
Complementary base pairs are held together by?
hydrogen bonds
5-membered rings of sugar
Pentoses
2 types of pentoses
RNA (hydroxyl group, OH)
Ribose
2 types of pentoses
DNA, no oxygen (H)
Deoxyribose
Derivatives of purine and pyrimidines that have a sugar linked to the ring of nitrogen
Nucleoside
Nucleosides are linked by?
B-N-glycosidic bond
- Forms the backbone of the DNA
- One chain runs in 5’ to 3’ direction while the other is 3’ to 5’
Phosphate
opposing orientation of the 2 nucleotide chains
Antiparallelism
links sugar base of one nucleotide and the phosphate group of the adjacent nucleotide
ester bonds
- Production of new DNA for cell division
- Proceeds in a 5’ to 3’ direction
DNA Synthesis or Replication
Absolute requirements for DNA synthesis
- Free 3’-OH group
- DNA template (ssDNA)
- Helicase binds to ORI protein of the parent and separates strands
- Unwinding begins at the A-T rich region and binding proteins keep strands apart
- Primase makes a short stretch of RNA on the DNA template
Step 1: Unwinding of DNA
Replication fork — appearance of the unwound DNA when it starts to form the leading and lagging strand
Step 2: Replication Fork Formation
- DNA polymerase adds DNA nucleotides to the RNA primer
- DNA polymerase proofreading activity checks and replaces incorrect bases
Step 3: DNA Polymerase Replication
- The primary replicase enzyme that performs the elongation of the DNA strand
- It adds nucleotides first to the RNA primer and then grows the chain by creating the phosphodiester bonds
- It also has a 3’-5’ proofreading (exonuclease) function that removes incorrectly incorporated nucleotides
DNA Polymerase
- Continuous strand synthesis continues in a 5’-3’ direction in the leading strand
- Discontinuous synthesis produces Okazaki fragments on the 5’-3’ template of the lagging strand
Step 4: Formation of Okazaki Fragments
- Enzymes — remove RNA primers
- Ligase — seals sugar-phosphate backbone and joins Okazaki fragments together
- Replication is completed by filling in the gaps by DNA polymerase and DNA ligase
Step 5: Removal of RNA Primers
- DNA molecules are extremely long, thus, it is packed into a chromosome that, during cell division, is only 2 micrometers (millionths of a meter long)
- To fit inside the nucleus, the DNA molecule must fold so tightly that its compacted length shrinks by a factor of 7,000
- DNA coils around proteins called histones that resemble beads on a string
DNA Synthesis
Enzymes in DNA Replication
unwinds parental double helix
Helicase
Enzymes in DNA Replication
stabilize separate strands
Binding proteins
Enzymes in DNA Replication
adds short primer to template strand
Primase
Enzymes in DNA Replication
binds nucleotides to form new strands
DNA polymerase
Enzymes in DNA Replication
joins Okazaki fragments and seals other nicks in sugar-phosphate backbone
Ligase
A polymer of purine and pyrimidine ribonucleotides linked together by 3’-5’ phosphodiester bridges analogous to those in DNA
RNA
- Usually double-stranded
- Thymine as a base
- Deoxyribose as the sugar
- Maintains protein-encoding information
- Cannot function as an enzyme
- Persists
DNA
- Usually single-stranded
- Uracil as a base
- Ribose as the sugar
- Carries protein-encoding information and controls how information is used
- Can function as an enzyme
- Short-lived
RNA
- Long straight chain of nucleotides
- Made in the nucleus during transcription
- Copies DNA and leaves through nuclear pores
- Contains the nitrogen bases (A, G, C, U (no T))
- Carries the information for several amino acids forming a specific protein
- Made up of 500 to 1000 nucleotides long
- Contains the sequence of 3 bases called codon
mRNA — Messenger RNA
start codon
AUG (methionine)
stop codon
UAA, UAG, UGA
- Single strand, 100-3000 nucleotides long
- Globular in shape
- Made inside the nucleus of a cell by the nucleolus
- Associates with proteins to form ribosomes
- Helps protein synthesis
rRNA — Ribosomal RNA
- Clover-leaf shape
- Single-stranded molecule with attachment site at one end for an amino acid
- Opposite end has three nucleotide bases called the anticodon
tRNA — Transfer RNA
- First step in gene replication
- Because the DNA is too big to exit the nucleus, a small copy of it must be created and exits to the cytoplasm
Transcription
splits the DNA strand molecule
RNA polymerase enzyme
3 stages of transcription
control point that determines which genes are transcribed
Initiation
3 stages of transcription
RNA nucleotides are added
Elongation
3 stages of transcription
a terminator sequence/region signals the end of transcription
Termination
- The mRNA is translated to synthesize proteins
- Each amino acid is formed by 3 nitrogenous bases
- In the cytoplasm, the ribosomes read the sequence of the RNA in groups of three bases
- An anticodon or complementary codon is matched to the RNA coding for a specific amino acid
Translation/Protein Synthesis
