DNA and RNA

Transcription

creation of mRNA from DNA, note only 1 DNA strand is needed for the template

Leading strand

flows from 5’ to 3’ and synthesizes DNA continuously.

Lagging Strand

flows from 5’ to 3’ and synthesizes DNA in chunks called Okazaki fragments, which are joined together by ligase.

Replication

Synthesis of complementary DNA strands by adding new nucleotides that are joined by phosphodiester bonds. (note this process is semiconservative)

Translation

The synthesis of a polypeptide using information from the messenger RNA. The cell must translate information gathered from the mRNA into the Amino Acid sequence of a polypeptide. Occurs on ribosomes; converts genotype to phenotype

The path of a DNA and RNA strand

Replication, Transcription, Translation

What does DNA ensure?

the continuity of hereditary information between generations

Semiconservative

One “old strand” and one completely new strand

Replication fork

A Y-shaped structure, the site of DNA replication, is created by DNA Helicase unwinding the double helix of DNA.

Codon

Triplet of mRNA bases

anticodon

triplet on tRNA bases

Standard start codon?

AUG (the Amino Acid for this is methionine)

Codon chart

gives you the Amino Acid sequence for each codon (ex: AUG = Methionine) note most Amino Acids are coded by more than 1 codon.

Initiation

rRNA in the ribosomes interacts w/ mRNA at start codon (AUG).

what is tRNA?

Used for the transfer of correct building blocks, such as Amino Acids, in translation, bringing the correct AA to the ribosomes, targeted via Anticodon, ensures AA sequence matches genetic information

what is mRNA

Messenger RNA carries genetic information from a cell’s nucleus to the ribosomes, where proteins are synthesized.

rRNA

ribosomal RNA, most abundant in cell (over 85% of total cellular RNA) composed of ribosomes and is used as a ribozyme (catalyzes the chemical reactions of protein synthesis).

Elongation

AA is transferred to the growing polypeptide chain, continues in the 5’ to 3’ direction as ribosomes moves down the message.

Termination

ends at a stop codon (UAA, UAG, UGA) and stops translating.

Common Ancestry

Almost all living organisms possess the same genetic code; therefore, this is a powerful piece of evidence for common ancestry.

Retroviruses

Retroviruses require an alternate flow of information (RNA to DNA) and require the enzyme Reverse Transcriptase. Viral DNA integrates into the host genome to be transcribed and translated for new viral progeny.

Flow of information

Prokaryotes DNA -> RNA -> Protein (Simultaneous) Ribosome & RNA Polymerase

Eukaryotes DNA -> RNA -> Protein (Sequential) Nucleus -> Cytoplasm/ER

Retroviruses RNA -> DNA -> RNA -> Protein Reverse Transcriptase

Important Metrics

3 bases makes 1 codon, 20 different standard Amino Acids

RNA and DNA comparision

Feature DNA RNA

Pentose Sugar: Deoxyribose Ribose

Nitrogenous Bases: A, G, C, Thymine; A, G, C, Uracil

Structure Double-stranded helix; usually single-stranded

Stability: Highly Stable (Storage) Less Stable (transient)

Chargaff’s Rule

30% Adenine, 30% Thymine, 20% Cytosine, 20% Guanine

Prokaryote Chromosomes

single circular chromosomes, not associated with histone proteins, found in the nucleoid region, allowing for rapid replication and gene expression in small cells.

Topoisomerase

Relaxes the DNA strand left tense after the helicase unwinds it. This also occurs by breaking, swiveling, and rejoining DNA strands.

RNA primers

Since DNA polymerase may not start a strand from scratch and can only add to it, RNA Primers are short sequences of RNA nucleotides

synthesized by Primase to provide an end for DNA synthesis.

DNA polymerase

DNA Polymerase is the primary enzyme that synthesizes new

strands of DNA by matching complementary nucleotides to the

template.

Adds nucleotides in 5' to 3' direction.

Requires an RNA primer to initiate.

Also provides proofreading capabilities.

Replication Accuracy

The error rate is extremely low (1 in 10 billion bases).

DNA polymerase proofreads as it goes.

Mismatch repair enzymes fix errors missed by

polymerase.

Essential for maintaining genetic stability.

Template Strand

The template strand (or antisense strand) is the one

actually read by RNA polymerase

Non-template strand

The Non-Template Strand (or coding/sense strand) has a

sequence matching the new RNA (except T vs U).

RNA synthesis

Occurs in the 5’ to the 3’ direction; to do this, it must read DNA in the 3’ to 5’ direction.

RNA in Eukaryotic cells

In eukaryotic cells, the initial mRNA transcript undergoes enzyme-mediated modifications before translation

5’ GTP cap

modified guanine nucleotide (GTP cap) is added to the 5’ end of the transcript. The cap is essential for ribosomal recognition and protects the mRNA from being worn down in the cytoplasm.

3’ Poly-A tail

the addition of this tail (which is a string of around 100-200 adenine nucleotides) occurs at the 3’ end and it makes the mRNA molecule more stable and also assists in the export of the mRNA from nucleus

Eukaryote Chromosomes

Multiple linear chromosomes, tightly packed, DNA is wrapped around histone proteins to form nucleosomes, which condense chromosomes during Mitosis.

Exons

Sequences that code for proteins, spliced together to form the final mature mRNA

Introns

Non-coding sequences, removed from the final transcript (excised/cut out)

Spliceosomes

Large complexes of proteins and small RNA molecules that

handle the excision of introns and retention of exons.

Precision is key: a single nucleotide error in splicing can ruin the

resulting protein's function.

Mutations

Change in codons resulting in a change in the nucleotide (could change corresponding amino acids).

Gene Regulation

Your body controls what proteins are made because not all genes require the same proteins

Prokaryote Gene Regulation

Prok. cells can turn off transcription of a group of genes called an operon. (RNA polymerase binds at the promoter to start transcription, and the operator acts as the start/stop switch.")

Operon

A group of genes, made of an operator and a promoter

Operators

can be turned off when a repressor protein binds to it blocking transcription

what can block repressors

Molecules found in the environment can attach to the repressor, preventing it from blocking transcription. This turns the gene on by allowing RNA polymerase to produce mRNA

Eukaryote Gene Regulation

RNA polymerase does not bind directly to the promoter, instead it is assisted by a specialized set of proteins called transcription factors

Transcription Factors

can cause genes to relax allowing transcription, can also cause DNA to coil tightly blocking RNA polymerase.

Point Mutation

a mistake is made in base pairing for one nucleotide can be nonsense, missense, silent mutation

Frameshift Mutation

A nucleotide is inserted or deleted, causing every nucleotide to change and the corresponding amino acid sequences to also change.