Transcription, translation, replication

DNA transcription

the first step of gene expression, where the cell's machinery copies a specific segment of DNA into a complementary messenger RNA (mRNA) molecule.

Synthesis of RNA from DNA

Gene expression

• process by which info carried by a gene has observable effects on an organism

• Base sequences do not determine the observable characterisitics of an organism

Non-coding sequences

Some base sequences that are transcribed do not code for polypeptides

Five-prime caps

modified nucleotide is added to the 5’ end. it has 3 phosphate groups instead of one. its base is guanine with an extra methane group

Poly (A) tails

between 100 and 200 adenine nucleotides are added to the 3’ end of the RNA. translation stops before the ribosome reaches the poly (A) tail

Introns

Sequences that will be removed from the primary RNA by enzymes called spliceosomes

Exons

Sequences that will be translated into amino acids

Template strand

the specific DNA strand that enzymes use as a guide to create an RNA molecule during transcription

RNA polymerase

the primary enzyme responsible for transcription, the first step in gene expression. It unzips the DNA double helix and builds a complementary RNA molecule using a DNA template strand

Promoter sequence

specialized regions of DNA located immediately upstream (at the 5' end) of a gene. They serve as critical "landing pads" for RNA polymerase and regulatory proteins, dictating exactly where transcription begins, which DNA strand to copy, and how often the gene is expressed

Non-Template strand

the DNA strand not directly used by RNA polymerase during transcription. Instead, it serves as a reference point, featuring the exact same nucleotide sequence and orientation as the resulting mRNA (with uracil replacing thymine).

DNA replication

Replication of DNA with base sequences identical to exisiting strands

Replication is required for

1. reproduction

2. growth and tissue replacement

DNA Proofreading

Correct errors, prevent mutation in DNA replication

• occurs immediatly after a mismatch

• In prokaryotes its done by DNA polymerase III

Leading strand

Synthesized continuously in the same direction the replication fork is moving. It only requires one initial RNA primer and grows smoothly. [1, 2, 3]

Lagging strand

Synthesized discontinuously in the opposite direction of the replication fork's movement. It is built in short segments called Okazaki fragments, each requiring its own RNA primer and later joined together by DNA ligase.

Continious

The DNA unwinds in the same direction that the polymerase is moving. The enzyme synthesizes the new strand seamlessly in one long, uninterrupted motion.

Discontinious

Because the lagging strand runs in the opposite direction, the polymerase is forced to move away from the unwinding replication fork. [1, 2]

Okazaki fragments

short, newly synthesized DNA sequences formed on the lagging strand during DNA replication.

DNA primase

an enzyme that synthesizes a short RNA segment, known as a primer, complementary to a single-stranded DNA template.

DNA polymerase I

Removing RNA primers from the lagging strand during replication and filling the resulting gaps with DNA

DNA polymerase III

the primary, highly processive enzyme complex responsible for prokaryotic chromosomal DNA replication. It synthesizes new DNA strands for both the leading and lagging strands and features built-in \(3' \to 5'\) exonuclease "proofreading" capabilities to minimize replication errors.

DNA ligase

stitch together the short, newly synthesized fragments of DNA—called Okazaki fragments—on the lagging strand

Translation

the process where cells use genetic information from messenger RNA (mRNA) to build proteins

Modifications of polypeptides

covalent alterations made to a polypeptide chain during or after its synthesis.

degeneracy

multiple codons (DNA base triplets) translate into the same amino acid

mRNA

messenger RNA, is a naturally occurring molecule in your cells that acts as a set of instructions. It carries the code from your DNA to the cell's protein-making factories, telling them exactly how to build the proteins your body needs to survive and function

rRNA

the non-coding RNA that serves as the primary structural and catalytic core of ribosomes. It acts as the "factory" where proteins are assembled, making up about 80% of total cellular RNA

tRNA

a small RNA molecule that acts as an adaptor during protein synthesis. It translates the genetic code by matching specific messenger RNA (mRNA) sequences with their corresponding amino acids, building the polypeptide chains that make up proteins.

Small subunit

decodes genetic instructions by binding directly to messenger RNA (mRNA) and scanning it to find the start codon (usually AUG).

Large subunit

it is responsible for catalyzing peptide bonds between amino acids and provides the structural tunnel that the newly forming polypeptide chain passes through as it is being synthesized

Polypeptide bond

the biological process where a ribosome decodes a messenger RNA (mRNA) sequence into a functional polypeptide chain.

Codon

a sequence of three consecutive nucleotides in DNA or messenger RNA (mRNA) that functions as a single unit of genomic information

Anticodon

a sequence of three nucleotides found on a transfer RNA (tRNA) molecule

Start codon

the first sequence of three nucleotides (a codon) in a messenger RNA (mRNA) transcript that is translated by a ribosome to signal the beginning of protein synthesis

Stop codon

a sequence of three nucleotides in DNA or messenger RNA (mRNA) that signals the cell to halt the synthesis of a protein