Ramp-Up Biology: Transcription & Translation

Deoxyribonucleic Acid (DNA)

the polymer that genes are made of in all cells, both prokaryotic and eukaryotic

• has two strands that are antiparallel (5’ end of one strand faces the 3’ end of the other strand

• complementary (A pairs with T, and G pairs with C)

• stable

• the genetic material of the cell

Ribonucleic Acid (RNA)

nucleic acid that is the product of transcription

• more reactive

• unstable compared to DNA

Nucleotide

the monomer of nucleic acids (ribonucleotide NTP for RNA and deoxyribonucleotide dNTP for DNA)

• comprised of nitrogenous base (ATGC in DNA and AUGC in RNA) covalently bonded to a pentose sugar (ribose in NTP and deoxyribose in dNTP) which is bonded to phosphates

DNA Replication

the process by which the genome’s DNA is copied in cells

• before a cell divides, it must first copy (or replicate) its entire genome so that each resulting daughter cell ends up with its own complete genome

  • each DNA template strand is read from 3’ to 5’ to make a complementary DNa strand from 5’ to 3’

Transcription

the process of making an RNA copy of a gene’s DNA sequence

• RNA transcribed can be mRNA (coding), tRNA (noncoding), and rRNA (noncoding)

  • the mRNA carries the gene’s protein information encoded in DNA

• only one DNA strand of the gene serves as a DNA template strand

  • this strand is read 3’ to 5’ by RNA polymerase enzyme to make the transcript in a 5’ to 3’ direction

Translation

the process of translating the sequence of a messenger RNA molecule to a sequence of amino acids during protein synthesis

• mRNA is read in a 5’ to 3’ direction from the start coding till the translation machine encounters the stop codon

Central Dogma

theory that states that genetic information, in all cells, flows from DNA to RNA to proteins

Gene Expression

a process by which the genetic information in a DNA sequence is turned into a functional product (EX: protein or noncoding RNA)

• all cell types in our body have the SAME genes, but express different sets of genes

• accounts for the difference in their shapes, sizes, and functions

Gene

a sequence of nucleotides that codes for a functional gene product (protein or noncoding RNAs)

• unit of genetic informaion

Promoter Sequence

a regulatory sequence of the gene to which RNA polymerase enzyme bids to start transcription

• this sequence is NOT transcription

Transcribed Region of a Gene

this is the part of a gene that extends from transcription start site to transcription stop site and gets transcribed

Alternative Splicing

a cellular process in which exons from the same gene are joined in different combinations, leading to different, but related, mRNA transcripts

• occurs in eukaryotic cells

Exon

the portion of a gene that codes for amino acids

Intron

a portion of a gene that intervenes between two successive exons

• doesn’t code for amino acids

• spliced out during alternative splicing

• has a splice donor site at its start (5’ end of mRNA) and a splice acceptor site at its end (3’ end of mRNA)

Amino Acids

monomer of proteins

Ribosomes

complex of rRNA and proteins is the factory for protein translation

(Open) Reading Frame

a portion of a DNA molecule that, when translated into amino acids, contains no stop codons

Codon

a trinucleotide sequence of DNA or RNA that corresponds to a specific amino acid

• part of the open reading frame of a gene

Start Codon

a trinucleotide sequence within a messenger RNA (mRNA) as it is read from 5’ to 3’

• determines the reading frame of mRNA that gets translated into a protein

Stop Codon

a trinucleotide sequence within a messenger RNA (mRNA) molecule that signals a halt to protein synthesis

• there is no tRNA corresponding to stop codon

Mutation

a change in a DNA sequence

• some are nonconsequential (some mutations in the intron regions of a gene) whereas others may be consequential (they may alter the rate of protein synthesis - mutations in the promoter sequence of a gene) and others may change the sequence of amino acids in the protein

Point Mutation

when a single base pair is altered, deleted, or inserted

Nonsense Mutation

the substitution of a single base pair that leads to the appearance of a premature stop codon where previously there was a codon specifying an amino acid

Missense Mutation

when the change of a single base pair causes the substitution of a different amino acid in the resulting protein

Frameshift Mutation

a type of mutation involving the insertion or deletion of a nucleotide in which the number of deleted base pairs is not divisible by three S

Silent Mutation

a point mutation in the gene that does not change the amino acid sequence of the resulting protein