Structure and Function of DNA and Protein Synthesis

Comprehensive vocabulary flashcards covering DNA structure, packaging into chromosomes, the genetic code, protein synthesis (transcription and translation), and the molecular mechanism of semi-conservative DNA replication.

DNA (Deoxyribonucleic acid)

A molecule found in all cells of all organisms that carries instructions for making proteins and is capable of self-replication.

Nucleotides

The repeating units and building blocks of DNA, each consisting of one $5$-carbon sugar, one phosphate group, and one nitrogen base.

Double helix model

The twisted spiral shape formed by how nucleotides join together in a DNA molecule.

Nitrogenous bases

The four different bases in a DNA molecule: Cytosine ($C$), Guanine ($G$), Adenine ($A$), and Thymine ($T$).

Phosphodiester backbone

The structural frame of DNA consisting of alternating phosphate and sugar molecules, where the phosphate bonds covalently to the sugar of the next nucleotide.

Antiparallel strands

The arrangement of DNA strands running in opposite directions, one from $3'$ to $5'$ and the other from $5'$ to $3'$.

Hydrogen bond

A weak bond that holds paired nitrogen base molecules together in the middle of the DNA molecule.

Base pairing rules

The specific bonding where Adenine joins Thymine ($A-T$) with $2$ hydrogen bonds, and Cytosine joins Guanine ($C-G$) with a $3$-hydrogen bond.

Histones

Proteins around which strands of DNA are looped, coiled, and wrapped to facilitate neat packaging within the nucleus.

Chromatin

The coiled state of DNA when it is wrapped around histone proteins.

Supercoiling

The process through which chromatin is further condensed to be packaged into structures called chromosomes.

Chromosomes

Structures made of packaged chromatin; humans have $23$ pairs or $46$ in total, each containing one DNA molecule.

Chromatid

One of two identical halves of a duplicated chromosome, held together by a centromere.

Centromere

The region of a chromosome that holds two chromatids together.

Genes

Segments of DNA on a chromosome that contain the code and instructions for the construction of a particular protein.

Amino acids

The building blocks of proteins, which are linked in long chains and folded into a $3D$ shape; there are $20$ different types.

Codon

A sequence of three nitrogen bases read together that represents one specific amino acid.

Transcription

The process by which a gene's DNA sequence is copied into messenger RNA ($\text{mRNA}$).

RNA polymerase

The enzyme that binds to the promoter, unwinds DNA, and joins nucleotides to form a complementary strand of $\text{mRNA}$.

Initiation (Transcription)

The beginning of transcription when RNA polymerase binds to the promoter region of a gene.

Elongation (Transcription)

The stage of transcription involving the addition of nucleotides to the growing $\text{mRNA}$ strand.

Termination (Transcription)

The end of transcription where the completed $\text{mRNA}$ strand detaches from the DNA.

Translation

The process in which the genetic code in $\text{mRNA}$ directs ribosomes to connect amino acids together to produce proteins.

Transfer RNA ($\text{tRNA}$)

A molecule that carries individual amino acids to the ribosome and matches its anticodon to the $\text{mRNA}$ codon.

Anticodon

A sequence of $3$ nitrogen bases on a loop of $\text{tRNA}$ that is complementary to a codon on the $\text{mRNA}$ molecule.

Ribosomal RNA ($\text{rRNA}$)

RNA found in ribosomes that assists in the creation of peptide bonds between amino acids.

Semi-conservative replication

The method of DNA replication where each new molecule consists of one original parental strand and one newly synthesized strand.

Helicases

Enzymes that unwind the parental double helix during DNA replication.

DNA polymerase

The enzyme responsible for synthesizing the new DNA strand by adding nucleotides in the $5' \rightarrow 3'$ direction.

Leading strand

The DNA strand that is synthesized continuously in the $5' \rightarrow 3'$ direction toward the replication fork.

Lagging strand

The DNA strand synthesized discontinuously in short segments called Okazaki fragments.

Primase

An enzyme that synthesizes a short RNA primer to provide a starting point for DNA polymerase.

Okazaki fragment

Short sequences of DNA nucleotides synthesized discontinuously on the lagging strand.

DNA ligase

The enzyme that joins Okazaki fragments together on the lagging strand to form a continuous DNA strand.