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Flashcards on DNA and RNA structure, replication, transcription, translation, and related concepts.

Francis Crick's definition of a genetic material

A genetic material must duplicate itself and control the development of the rest of the cell in a specific way.

Friedrich Miescher (1871)

Isolated nuclei from white blood cells in pus and found an acid substance with nitrogen and phosphorus.

Archibald Garrod (1902)

Linked inheritance of inborn errors of metabolism.

Frederick Griffith (1928)

Worked with Streptococcus pneumoniae bacteria, which exists in two types: Type S (smooth) and Type R (rough).

Difference between Streptococcus pneumoniae Type S and Type R

Type S is enclosed by a capsule, which will not be recognized by the immune system. Type R has no capsule and is exposed.

Oswald Avery, Colin MacLeod, and Maclyn McCarty (1944)

Treated lysed S bacteria with protease and DNase to destroy protein and DNA, respectively.

Alfred Hershey and Martha Chase (1953)

Used Escherichia coli bacteria infected with a virus and grew a batch of virus in a medium containing 35S and 32P in a blender experiment.

Bacteriophage

A virus that infects bacteria.

Phoebus Levine

Identified the 5-carbon sugars ribose in 1909 and deoxyribose in 1929 and discovered the chemical distinction between RNA and DNA.

Erwin Chargaff (1951)

Analyzed base composition of DNA from various species and observed regular relationships: A+G = T+C.

Purines and Pyrimidines

AG are purines, and TC are pyrimidines and should be in equal amounts.

Rosalind Franklin and Maurice Wilkins (1952)

Used X-ray diffraction to obtain an image of DNA's helix structure; distinguished two forms of DNA using 'photo 51'.

James Watson and Francis Crick

Produced the 1st 3D model of DNA, using ideas originally from Rosalind Franklin.

Gene

A section of a DNA molecule.

Nucleotide

A single building block of DNA, composed of a deoxyribose sugar, a phosphate group, and a nitrogenous base (A, G, T, C).

Phosphodiester bonds

Form between the deoxyribose sugars and the phosphates, creating a continuous sugar-phosphate backbone.

Antiparallelism

DNA consists of two chains of nucleotides in an antiparallel configuration.

Complementary base pairs

The specific pairing of purines and pyrimidines via hydrogen bonds: A=T (2 H+ bonds) and G=C (3 H+ bonds).

DNA Directionality

One strand runs in a 5' to 3' direction, and the other runs in a 3' to 5' direction.

DNA condensation

Scaffold proteins form frameworks that guide DNA strands; DNA coils around histones; chromosome substance is called chromatin

Nucleosome

A DNA strand + Histone.

RNA

The bridge between gene and protein.

RNA Template

Bases of an RNA sequence are complementary to those of one strand of the double helix, called the template strand.

RNA Polymerase

Builds an RNA molecule.

Coding strand

The nontemplate strand of the DNA double helix.

RNA structure compared to DNA

Usually single-stranded, contains uracil instead of thymine, ribose as the sugar, and can function as an enzyme.

Major types of RNA

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

Replication

DNA to DNA.

Transcription

DNA to RNA.

Translation

RNA to Protein.

Function of mRNA

Encodes amino acid sequence.

Function of rRNA

Associates with proteins to form ribosomes, which structurally support and catalyze protein synthesis.

Function of tRNA

Transports specific amino acids to the ribosome for protein synthesis.

mRNA

Carries information that specifies a particular protein. Three mRNA bases in a row form a codon, which specifies a particular amino acid.

Anticodon

A three-base sequence on one loop of a transfer RNA molecule that is complementary to an mRNA codon and connects the appropriate amino acid and its mRNA.

Three DNA replication models

The semiconservative model, the conservative model, and the dispersive model.

DNA Replication

Process to ensure that the DNA is duplicated; happens during the S phase of cell division.

Matthew Meselson and Franklin Stahl, 1957

Demonstrated the semiconservative mechanism of DNA replication using labeled replicating DNA from bacteria with a heavy form of nitrogen.

Three phases of DNA replication

Initiation, Elongation, and Termination.

Helicase

Separate or unzip the strands.

Binding Proteins

Keep the strands apart.

Primase

Insert Promoter and starts the sequence.

DNA Polymerase

Add Nucleotides.

Ligase

Catalyzes the formation of covalent bonds in the sugar-phosphate backbone of a nucleic acid.

Origins of replication

Specialized sites where DNA replication starts.

Replication forks

The sites at which single-stranded DNA is exposed, and at which DNA synthesis occurs.

Leading strand

The strand synthesized in the 5’ to 3’ direction.

Lagging strand

Replicated discontinuously as fragments, which are later joined to form a continuous strand.

Lagging strand (3’ to 5’)

Nucleotides here are in fragments – Okazaki fragment.

Exome

DNA of the human genome which encodes protein

Intron

Unused part of the genome.

Exon

Expressed part of the genome.

Coding Strand

Sequence is the same as the RNA sequence that is produced, with the exception of U replacing T.

Template Strand

Its code is the complement of the RNA that is produced.

Transcription

Key enzyme is RNA polymerase.

RNA polymerase

Reads the template from 3’ to 5’.

Transcription

Coding strand – RNA (A = U : C = G) , Template Strand – DNA

RNA Processing

A methylated cap is added to the 5’ end, a poly A tail is added to the 3’ end, splicing occurs, mRNA is proofread, and the mature mRNA is sent out of the nucleus.

Translation

Assembles a protein using the information in the mRNA sequence.

Translation

Divided into three steps: Initiation, Elongation, and Termination.

Translation Initiation

The leader sequence of the mRNA forms H bonds with the small ribosomal subunit. Start codon: AUG.

Primary (1 degree) structure

Amino acid sequence.

Secondary (2 degree) structure

Folding; Alpha helix and beta-pleated sheet.

Tertiary (3 degree) structure

3D structure / further folding.

Quaternary (4 degree) structure

Interaction of subunits (e.g. Hemoglobin).

Chaperone Proteins

Stabilize partially folded regions and prevent a protein from getting stuck; developed into to treat diseases

Misfolded proteins

Tagged with ubiquitin and taken to a proteasome, a tunnel-like multiprotein structure.