USMLE PREP #1

Replication

DNA to DNA (DNA Synthesis)

Transcription

DNA to RNA (RNA Synthesis), occurs in interphase

Translation

RNA to Protein (cytoplasm)

Reverse Transcription

RNA to DNA (Retroviruses)

Gene Expression

Turns on gene (activates transcription and translation)

DNA

What is bigger DNA or RNA?

Fragmenting

Breaks DNA into smaller pieces so its easier to analyze

Interphase

G0, G1, S, G2 (everything but M)

G0

This cell cycle phase does NOT divide (most cells are in this- neurons, muscle cells, non-nucleated RBCs)

G1 Cells

Cells that get ready to divide (nucleated red cells, epithelial cells, hair cells) 46 chromosomes and 46 chromatids (have not divided yet)

G1 Checkpoint

Uses signal transduction, triggered by hormones, to decide when a cell should enter S phase (DNA replication) Tyrosine Kinase Receptor (TKR) plays a key role

Adenine

Thymine

Uracil

Guanine

Cytosine

Nucleoside

Base and a sugar

Nucleotide

Base, Sugar, and Phosphate (AMP, ADP, ATP)

Synthesis (S)

Phase in cell cycle that replicates DNA (DNA synthesis) 92 chromatids (46 Chromosomes)

Nucleic Acids

These are made up of nucleotides joined together by phosphodiester bonds.

There is usually a 5’ phosphate and a 3’ hydroxyl group

Nucleosomes

DNA wraps around histones to form

Positively

Histones are () charged

10 nm fiber

DNA + histone octamer (nucleosomes)

30 nm fiber

Nucleosomes added H1 histones (tighter package)

Higher-order chromatin

Nucleosomes with H1 histones and scaffolding proteins (even more condensed)

Heterochromatin

Very tightly packed, inactive (dark staining, inactive)

Euchromatin

Loosely packed, active (light staining, open and used for transcription)

Barr Bodies

One female X chromosome is inactive

Denaaturation

DNA strands are separated (around 92-95 degrees Celsius) PCR

Annealing

Primers bind (or renature) to the single stranded DNA (50 to 65 degrees Celsius)

Extension

DNA Polymerase extends the primers to form a new strand (72 degrees Celsius)

HIV

() has reverse transcriptase and requires a primer but lacks proof reading activity (does not have 3’ exonuclease activity) 

Telomerase

Prevents chromosomes from shortening with # of replications (reverse transcriptase activity)

hMLH2, hMLH1

are the genes that finds the error and excises it, respectively 

Lynch Syndrome

(DNA Instability) that exhibits incomplete pentrance (one good gene, one bad gene, NO CANCER, but you will still have Lynch, you need two for to develop pathology (cancer))

Uracil

Cytosine Deamination creates 

3’ exonuclease

() is the proofreading enzyme

5’ exonuclease

() removes RNA primer

p53

() prevents damaged cells from going into S phase, induces apoptosis (suppresses tumor formation)

kDa, Daltons

Cells can be damaged in G1 like p53 (protein 53, 53 means 53(), 53,000 ())

Li-Fraumani Syndrome

If P53 turns mutated damaged DNA cells go into S phase causing ()

Loss of Function Mutations

Tumor Suppressive Genes  (mutated p53, p53 does not work, creating cancer)

Gain of Function Mutations

Where a gene is mutated to make the gene “turn on” when it is not supposed to be “on”, creating cancer

primer

DNA Polymerase has to see a () on a chromosome to start replication

Promoter

RNA Polymerase binds to the () in order to start transcription, double stranded DNA

Gene

double stranded DNA, but only one stand is used as a template

Template Strand

Strand used in transcription, complementary to mRNA

Coding Strand

Strand NOT used in transcription, but is IDENTICAL to mRNA (U/T)

read

DNA is () in 3’ to 5’ direction

RNA

() is synthesized in the 5’ to 3’ direction

upstream

Promoter is always () to the gene

mRNA

made in euchromatin portion of the nucleus (light stained)

tRNA

made in euchromatin portion of the nucleus (light stained)

rRNA

made in nucleolus

Coding Strand

Complementary and anti-parallel to the template strand

Operon

Polycistronic gene region is also known as the

protein information

UTR (Untranslated Region) is a region with no ()

exons or introns, translational processing

Prokaryotic gene expression does not have () or ()

Stem-loop sequence

terminates RNA transcription (stretch G and C)

promoter

The () is replicated since it is DNA

operon

makes multiple genes in one RNA

shine dalgarno sequence

RNA binds to the () in the operon

rifampin

inhibits transcription (RNA polymerase) in bacteria (used to treat TB and meningitis)