Intro Life Science - Chapter 9

Central Dogma

The flow of genetic information from DNA to RNA to Protein: DNA replication (S phase), transcription (DNA to mRNA), and translation (mRNA to proteins)

Chargaff's Rule

Showed that DNA nucleotides (monomers) had two types found in equal amounts: A=T and C=G

Nucleotide

A monomer made up of a sugar, phosphate group, and a nitrogenous base; the base determines whether it is A, C, T, or G

Pyrimidines

Cytosine (C) and Thymine (T); nitrogenous bases with only one ring

Purines

Guanine (G) and Adenine (A); nitrogenous bases with two rings (remember: Purina dog food = two bowls)

Sugar phosphate backbone

The outside of the DNA strand that must be broken apart to access the genetic information (bases)

Antiparallel

DNA's two strands run in opposite directions (one runs 5' to 3', the other 3' to 5')

DNA polymerase

The enzyme that builds (polymerizes) new strands of DNA from monomers; can only synthesize in the 5' to 3' direction (but runs 3’ to 5’ on the original strand)

Nucleus

Where eukaryotic cells store their DNA

Nucleoid

The area in the cytoplasm of prokaryotic cells where the chromosome lies (prokaryotes have no nucleus)

Semiconservative Model of DNA Replication

Each parent strand is used as a template to make a complementary daughter strand; each new DNA molecule contains one original and one new strand

Origin of replication

A specific sequence of DNA where replication begins

Helicase

The protein/enzyme that separates (unwinds) the two DNA strands during replication

Replication fork

The Y-shaped point where DNA strands are being pulled apart by helicase; like the opening in a zipper

RNA primer

A short RNA sequence that tells DNA polymerase where to start; anneals (binds) to the DNA template strand

Leading strand

The strand of DNA that is synthesized continuously in one direction (5' to 3') during replication

Lagging strand

The strand of DNA that is synthesized in short stretches (Okazaki fragments) because DNA polymerase must repeatedly jump back

Okazaki fragments

The short, broken fragments of DNA synthesized on the lagging strand during replication

DNA ligase

An enzyme that acts like molecular glue, joining Okazaki fragments into a continuous strand

Telomere

The protective cap at the very edge of a chromosome that cannot be copied by DNA polymerase

Telomerase

The enzyme that extends telomeres, keeping chromosomal DNA from shrinking with each replication

Mutation

A DNA replication error; a change in the nucleotide sequence of DNA

Mismatch repair

A repair process where the incorrect base is detected after replication; repair proteins remove the error by nuclease action and fill the gap with the correct base

Nucleotide excision repair

A repair process that fixes DNA damage caused by UV light and certain chemical agents (e.g., thymine dimers)

Thymine dimers

Abnormal bonds formed between two adjacent thymines due to UV light exposure; can cause problems in future DNA replication

Transcription

The process of copying DNA into mRNA; occurs in the nucleus

Initiation (Transcription)

The first stage of transcription where the promoter signals where mRNA transcription begins

Promoter

A DNA sequence that signals where transcription should begin; recruits RNA polymerase to start transcribing a gene

Elongation (Transcription)

The stage where RNA polymerase reads along the DNA template strand and produces mRNA

RNA polymerase

The enzyme that reads DNA and produces (synthesizes) RNA during transcription

Termination (Transcription)

The final stage where RNA polymerase stalls, stops producing RNA, and releases the completed mRNA from the DNA

Uracil

The nitrogenous base in RNA that replaces thymine (U instead of T); RNA uses A, C, G, U

Ribosome

Made of a large and small subunit; reads mRNA and produces proteins during translation

rRNA (ribosomal RNA)

The type of RNA that holds the ribosome together, acting like structural glue

tRNA (transfer RNA)

The translator molecule that carries amino acids to the ribosome and matches them to mRNA codons during translation

Codon

An mRNA nucleotide triplet (set of three bases) that codes for one amino acid

Genetic code

The chart/system showing which codon translates to which amino acid

Start codon (AUG)

The codon that tells the ribosome where to begin translation; codes for the amino acid methionine (remember: AUGust starts the school year)

Stop codons (UAA, UAG, UGA)

Three codons that signal the end of translation; they do not code for any amino acid

Translation

The process of converting the mRNA nucleotide sequence into a chain of amino acids (protein) at the ribosome

Translation initiation

The small ribosomal subunit scans mRNA until the tRNA anticodon recognizes the start codon (AUG) and brings methionine

Anticodon

The three-base sequence on tRNA that is complementary to an mRNA codon (e.g., UAC is the anticodon for AUG)

Elongation (Translation)

The large ribosomal subunit joins the small subunit; successive tRNAs bring amino acids that are added to the growing polypeptide chain

Polypeptide chain

The chain of amino acids produced during translation that will fold into a functional protein

Translation termination

Occurs when the ribosome reaches a stop codon; ribosome subunits dissociate and the completed polypeptide is released

Exons

The portions of pre-mRNA that are expressed (kept) in the final mature mRNA

Introns

The in-between portions of pre-mRNA that are removed before the mRNA exits the nucleus

Splicing

The process of removing introns from pre-mRNA so only exons remain in the final mRNA

Substitutions

A type of point mutation where one nucleotide is replaced by another

Insertion/Deletion

A type of mutation where nucleotides are added or removed from the DNA sequence

Silent mutations

Mutations that cause no change in amino acid sequence; the protein remains the same

Missense mutations

Mutations that change one amino acid for a different one in the protein

Nonsense mutations

Mutations that introduce a premature stop codon, shortening the protein

Frameshift mutations

Mutations caused by insertions or deletions that shift all downstream codons, altering the entire amino acid sequence after the mutation

DNA Replication (Steps)

1. Helicase unwinds DNA at origin of replication. 2. RNA primer binds. 3. DNA polymerase builds new strands 5’ to 3’. 4. Leading strand: continuous. Lagging strand: Okazaki fragments. 5. Ligase joins fragments. 6. Telomerase extends telomeres.

Transcription (Steps)

1. Initiation - promoter signals start, RNA polymerase binds. 2. Elongation - RNA polymerase reads DNA, produces mRNA. 3. Termination - RNA polymerase stops, releases mRNA.

Translation (Steps)

1. Initiation - small subunit finds start codon (AUG), tRNA brings methionine. 2. Elongation - large subunit joins, tRNAs add amino acids to polypeptide chain. 3. Termination - stop codon reached, ribosome dissociates, polypeptide released.

RNA Processing (Steps)

1. Pre-mRNA produced. 2. Introns spliced out. 3. Exons joined. 4. Mature mRNA exits nucleus.

Mismatch Repair (Steps)

1. Incorrect base added during replication. 2. Repair proteins detect the error. 3. Nuclease removes incorrect base. 4. Gap filled with correct nucleotide.

Nucleotide Excision Repair (Steps)

1. UV light causes thymine dimers. 2. Damage detected. 3. Damaged segment cut out. 4. Gap filled with correct nucleotides.