IBDP Bio (2025) - D1.2 Protein Synthesis

Amino acid

building block of proteins consisting of a basic amino group (NH2), an acidic carboxylic group (COOH), a hydrogen atom (-H), and an organic side group (R) attached to the carbon atom.

Anticodon

three consecutive bases on tRNA that are complementary to a codon on mRNA.

Codon

each sequence of three bases standing for one of the 20 possible amino acids.

Complementary base pairing

is the standard arrangement of bases in nucleotides in relation to their opposite pairing, such as cytosine paired with guanine and adenine with thymine (or uracil in RNA).

degeneracy

there are more codons (64) than there are amino acids to be coded, so most amino acids are coded by more than one code.

Genetic code

the order of bases in DNA that determines the sequence of amino acids in proteins.

Hydrogen bonds

a chemical bond in which a hydrogen atom of one molecule is attracted to an electronegative atom of another molecule.

Messenger RNA (mRNA)

a type of RNA that attaches to ribosomes and specifies the sequence of amino acids in a protein.

Nucleotides

the building blocks of nucleic acids consisting of a five-carbon sugar, a nitrogenous base, and a phosphate group.

Polypeptides

a polymer of amino acids joined together by peptide bonds.

Ribosomes

cell organelle that functions as the site of protein synthesis.

RNA polymerase

an enzyme that links together the growing chain of RNA during transcription.

Transcription

when the DNA sequence of bases is converted into mRNA.

Translation

when the sequence of bases on mRNA is decoded into an amino acid sequence (proteins).

Transfer RNA (tRNA)

an RNA molecule that brings specific amino acids that match the codons in the mRNA.

RNA

single-stranded nucleic acid that contains the sugar ribose

initiation of translation

brings together mRNA, a tRNA with the first amino acid, and the two ribosomal subunits

elongation (translation)

codon recognition, peptide bond formation, translocation

Sense strand of DNA

The strand of DNA that is read to make mRNA during transcription

Antisense strand of DNA

The noncoding DNA strand, which is complementary to
mRNA and serves as the template for RNA synthesis. Also called the transcribed strand.

free RNA nucleotides

monomers used to create an RNA polymer

Adenine

The base that pairs with Thymine in DNA

Thymine

The base that pairs with Adenine in DNA

Guanine

The base that pairs with Cytosine in DNA

Cytosine

The base that pairs with Guanine with DNA

Uracil

Nitrogen base that pairs with adenine in RNA.

gene expression

The process by which information encoded in DNA directs the synthesis of proteins or, in some cases, RNAs that are not translated into proteins and instead function as RNAs.

rRNA

ribosomal RNA; type of RNA that makes up part of the ribosome

small ribosomal subunit

Part of ribosome that recognizes mRNA transcripts and initiates translation

large ribosomal subunit

joins amino acids to form a polypeptide chain

triplet code

3 bases of DNA that code for a single amino acid

Universality of DNA

all organisms use the same genetic code

stop codon

UAG, UAA, or UGA; the codon that ends all RNA.

start codon

AUG (methionine)

peptide bond

covalent bond formed between amino acids

condensation reaction

a chemical reaction in which two or more molecules combine to produce water or another simple molecule

elongation (translation)

codon recognition, peptide bond formation, translocation

insertion mutation

a mutation in which one or more nucleotides are added to a gene

deletion mutation

a mutation in which one or more pairs of nucleotides are removed from a gene

substitution mutation

Mutation in which a single base is replaced, potentially altering the gene product.

silent mutation

A mutation that changes a single nucleotide, but does not change the amino acid created.

frameshift mutation

mutation that shifts the "reading" frame of the genetic message by inserting or deleting a nucleotide

sickle cell anemia

a genetic disorder that causes abnormal hemoglobin, resulting in some red blood cells assuming an abnormal sickle shape