6) Molecular Genetics Cheat Sheet

DNA

Contains hereditary information of te cell

• double stranded

• ATGC nucleotides

RNA

functions vary by RNA molecule

• AUGC

mRNA

Messenger RNA is the single-stranded template for protein synthesis

tRNA

transfer RNA that is clover-shaped and transports amino acid to its mRNA codon

rRNA

Ribosomal RNA that is globular and forms part of the ribosomes

DNA Replication

Copying of genetic information in cells

• DNA replication begins at origin of replication

• new bases added to complementary template

• One new strand made continuously (leading strand)

• One made in fragments (lagging strand)

Leading Strand

Synthesized continuously as DNA unzips

Lagging strand

synthesized discontinuously (producing okazaki fragments)

Okazaki Fragments

Short stretches of nucleotides formed as a lagging strand is synthesized

Primase

Creates a small strip of RNA primer. DNA polymerase needs this existing set of nucleotides from the primer to begin synthesizing a new strand of DNA

DNA Polymerase III

Synthesizes new DNA strand in 5’ → 3’ direction by adding nucleotides to an RNA primer

DNA Polymerase I

Removes RNA primer and replaces it with newly synthesized DNA

Ligase

Seals the aps in the phosphodiester backbone of DNA between Okazaki fragments

Telomere

Segment of DNA that are added to the ends of chromosomes to prevent loss of genomic info as chromosome ends wear down

Telomerase

Enzyme that creates telomeres

Translation

The synthesis of proteins based on the sequence of mRNA nucleotides

1) Initiation

2) Elongation

3) Termination

Translation Initiation

Small ribosomal subunit binds to mRNA and methionine tRNA binds to AUG start codon; large ribosomal subunit

Translation Elongation

tRNA brings amino acids to a growing polypeptide chains enter A site, then shift to P site, and finally to E site for removal

Translation Termination

Translation terminates when te stop codons (UAG, UAA, UGA) are encountered. These are recognized by release factors, which cause the newly made polypeptide chain to be released

RNA Splicing

The process of removing sections of pre-mRNA transcript that are absent in the mature mRNA and reconnecting the remaining exons

Exons:

Protein coding regions of the genome

Introns

Non-coding regions in mRNA that do not encode functional proteins

Alternative splicing

Process occurring during gene expression that allows for production of multiple protein types from a single gene when different combinations of exons are used

Transcription

Process of synthesizing RNA from a DNA template. A specific gene is bonded and transcribed. In DNA replication, entire genome is replicated

Transcription Initiation

RNA polymerase attaches to promoter region on DNA and unzips DNA into 2 strands

Transcription elongation

RNA polymerase synthesizes RNA nucleotides usin gonre DNA strand as template

Transcription termination

RNA polymerase reaches a special sequence, detaches from the DNA, and disassembles

RNA Splicing

the process of removing sections of pre-made RNA transcript that are absent in the mature mRNA and reconnecting the remaining exons

Exons

Protein coding regions of the genome

Introns

non-coding regions in mRNA that do not encode functional proteins

Alternative splicing

Process occurring during gene expression that allows for production of multiple protein types from a single gene when different combinations of exons are used

Translation

The synthesis of proteins based on the sequence of mRNA nucleotides

Translation Initiation:

Small ribosomal subunit binds to mRNA and methionine tRNA binds to AUG start codon; large ribosomal subunit joins to form a complete ribosome

Translation Elongation:

tRNAs bring amino acids a growing polypeptide chain(s) enter at A site, then shift to P site, and finally to E site for removal

Translation Termination

Translation terminates when the stop codons (AUG, UAA, UGA) are encountered. These are recognized by release factors, which cause the newly made polypeptide chain to be released

Point Mutation

A single nucleotide change causing substitution, insertion, deletion.

Silent Mutation

the codon is changes, but due to the redundancies in codons, the same amino acid gets incorporated as normal; protein function remains unchanged

Missense Mutation

results in a new codon that encodes a new amino acid

Nonsense mutation

converts an existing codon encoding an amino acid into a stop codon, prematurely signaling the cell to stop building a protein; it produces a truncated, usually non-functioning proteinf

forward mutation

changes a wild type allele to a mutant allele

backward mutation

changes a mutant allele to wild type

frameshift mutation

results in a shifted reasing frame of RNA transcript, causing amino acids to be translated and resulting in impaired protein structture

Wild type

mRNA sequence without any mutation

Base-pair deletion

Frameshift causing extensive missense

Base-pair insertion

Frameshift causing immediate nonsense

Plasmids

Small, circular double stranded DNA molecules that are separate from the main prokaryotic DNA

• carry genes that are non-essential but beneficial for survival

• replicate independently from main prokaryotic DNA

Operons

gene clusters that control transcription and consist of promoter, operator, structural genes

Promotor

DNA sequence where RNA polymerase attaches to

Operator

Region that can block the action of RNA polymerase if occupied by a repressor

structureal genes

genes that code for proteins that are to be produced

regulatory genes

genes that encode products that control the expression of other genesr

repressor

protein that binds to the operator of prokaryotic genes to decrease transcription

activator(enhancer)

protein that binds to prokaryotic operators to increase transcription and assists the attachment of RNA polymerase to promotor

Lac Operon

operon in prokaryotic cell that encodes genes required for processing of lactose

• presence of lactose induces the operon to produce lactose breakdown enzymes → rna polymerase can now transcribe operon

Trp Operon

A group of genes necessary to synthesize tryptophan in prokaryotic cells

• presence of tryptophan allows trp repressor to bind to operator. RNA synthesis blocked

• absence of tryptophan, RNA synthesis process

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Conjugation

DNA transferred from a living donor bacterium to a living recipient bacterium by cell-to-cell contact

• donor produces pilus(bridge) to send DNA or plasmid to recipient. Donor may transfer F plasmid containing gene that allows pilus to form

transformation

a competent recipient bacterium takes up free DNA from surrounding

Transduction

DNA is transferred from one bacterium to another by a bacteriophage

Genome

complete genetic information for an organism

• majority of human genome is non-coding DNA

Transcriptome

Set of all RNA molecules that can be produced by a cell

Proteome

complete set of proteins in an organism that are expressed

Location of Transcription and Translation in Prokaryotes

Cytoplasm

Location of Translation in Eukaryotes

Cytoplasm

Location of Transcription in Eukaryotes

Nucleus

Polycistronic

single mRNA codes for many proteins

• Prokaryotes

Monocistronic

A single mRNA codes for a single protein

• eukaryotes

DNA Methylation

Stops gene expression by tightening chromatin organization of DNA and without altering nucleotide sequence

• more difficult to access DNA for transcription

Histone Acetylation

Increases gene expression by loosening chromatin organization of DNA and making it more accessible for transcription

• histones have a tail made of lysine amino acids

  • if mutated, gene expression could be affected → increased or decreased

RNA interference

microRNA and small-interfering RNA silence genes by binding to mRNA

Temperature-dependent sex determination

• seen in reptiles

• gender determined by environmental temperature during thermosensitive period of embryonic development

1) Patter development : males cold, women warm (ex: turtles)

2) Patter II development: females cold/hot, males medium (crocs)

genomic imprinting

captain genes are expressed depending on which parent they are inherited from

• body only expresses the genes from one parents chromosome rather than both while the imprinted genes on the other chromosome are silenced via epigenetic mechanism

Angelman Syndrome

A (different) set of genes is only expressed on the mother’s chromosomes 15, while the father’s genes are imprinted.

• if the maternal copies of the gene are deleted or mutated, health conditions result

Prader-Willi Syndrome

A set of genes are only expressed on the father’s chromosome 15, while the mother’s genes are imprinted

• if the genes on the father’s copy are mutated or deleted, health conditions result