The Relationship Between Nucleic Acids and Proteins

These flashcards cover the fundamental relationship between nucleic acids and proteins, including DNA/RNA structure, gene expression (transcription, processing, translation), gene regulation (specifically the trp operon), and protein structural levels.

What is the definition of a monomer?

A monomer is a single atom, small molecule, or molecular fragment that forms a larger polymer when bonded with identical or similar monomers.

What are the two main types of nucleic acids defined in the lecture?

The two types are DNA ($Deoxyribonucleic acid$), which is the basis of an organism's genetic material, and RNA ($Ribonucleic acid$), which is typically single-stranded and involved in protein synthesis.

Where is DNA located in prokaryotic cells?

In prokaryotic cells, DNA is found in the cytosol as a single, circular chromosome and in small circular pieces called plasmids.

What is the function of histone proteins in eukaryotic cells?

Histones bind to DNA to form nucleosomes, helping to pack large DNA threads into the confined space of the nucleus.

Define the terms 'genome' and 'allele'.

A genome is an organism's complete DNA base sequence, while alleles are different versions of the same gene.

What are the three components of a nucleotide?

A nucleotide consists of a phosphate group, a five-carbon sugar ($deoxyribose$ or $ribose$), and a nitrogenous base.

Which nitrogenous bases are categorized as pyrimidines?

Cytosine ($C$), Thymine ($T$), and Uracil ($U$).

Which nitrogenous bases are categorized as purines?

Guanine ($G$) and Adenine ($A$).

What type of bond joins nucleotides in the sugar-phosphate backbone?

A phosphodiester bond.

Explain the antiparallel nature of DNA.

DNA consists of two strands running in opposite directions, one in a $5'$ to $3'$ direction and the other in a $3'$ to $5'$ direction.

According to the complementary base pairing rule, how many hydrogen bonds form between $C$ and $G$?

$3$ hydrogen bonds ($CG3$).

What is semi-conservative replication?

It is a process where the resulting DNA molecules contain one original conserved strand and one newly synthesized strand.

What role does DNA polymerase play in DNA replication?

DNA polymerase moves along the template strand, adding complementary nucleotides toward the $3'$ end of the new strand.

What are the three main forms of RNA mentioned in the notes?

Messenger RNA ($mRNA$), Transfer RNA ($tRNA$), and Ribosomal RNA ($rRNA$).

What is the purpose of RNA processing in eukaryotes?

RNA processing involves adding a methyl-G cap to the $5'$ end, a poly-A tail to the $3'$ end, and splicing to remove introns.

Explain the concept of a 'degenerate' genetic code.

The code is degenerate because multiple different DNA triplets can code for the same amino acid, providing tolerance to genetic mutations.

What is a promoter region?

A region upstream of a gene where RNA polymerase binds to initiate transcription; in eukaryotes, this often contains a $TATA$ box.

During transcription, in which direction is the pre-mRNA strand synthesized?

It is synthesized in the $5'$ to $3'$ direction.

What happens during the 'termination' stage of translation?

Translation ends when a stop codon is reached; no $tRNA$ corresponds to this codon, leading to the release of the polypeptide chain.

Distinguish between regulatory and structural genes.

Regulatory genes code for proteins like transcription factors that control the expression of other genes, while structural genes code for proteins involved in the actual structure or function of an organism.

How does high tryptophan levels affect the trp operon via repression?

Tryptophan binds to the repressor protein, activating it so it can bind to the operator and block RNA polymerase from transcribing structural genes.

What occurs during attenuation in the trp operon when tryptophan levels are high?

A terminator hairpin loop forms in the $mRNA$, causing RNA polymerase to detach prematurely before transcribing the structural genes.

What are the four levels of protein structure?

$1. Primary$, $2. Secondary$, $3. Tertiary$, and $4. Quaternary$.

What is the 'proteome'?

The proteome is the complete set of proteins expressed by a cell or organism.

Which organelles are primarily responsible for the modification and packaging of proteins for secretion?

The Rough Endoplasmic Reticulum ($ER$) and the Golgi apparatus.

What process is used to release protein-filled vesicles from the cell?

Exocytosis, which is a form of bulk transport that requires $ATP$.