Molecular Genetics 🧬

Factors of DNA

Deoxyribose, two stranded, helix, antiparallel, facing inwards

Factors of RNA

ribose, single stranded, varied shape

Purines are?

Adenine and Guanine

Pyrimidines are?

Thymine and Cytosine

number of h-bonds and if they double up or not.

Adenine (doubles up) → Thymine (single) = 2 H-bonds

Guanine (doubles up) → cytosine (single) = 3 H-bonds

How much DNA in a single human cell?

1.8m

how is DNA organized in human cell?

wrapped around proteins & tightly compacted into linear chromosomes. There are coding regions called “genes”

YES OR NO: is there a correlation between an organisms’ complexity and genome size?

NO

TRUE OR FALSE: genes are NOT evenly spaced along chromosomes, and each chromosome has different numbers of genes.

TRUE

Describe prokaryotic cell DNA organization.

One (usually circular) chromosomes but no nucleus (DNA roams in nucleoid). The gene compaction is formed in looped domains with supercoiling.

How does Bacteria Usually Replicate?

independently of genome.

TRUE OR FALSE: bacterial genes are transmitted through the process of mitosis.

FALSE: by conjugation

3 stages of cell cycle are?

Interphase, Mitosis, Cytokinesis

Is DNA Replication:

A) Semi-conservative

B) Conservative

C) Dispersive

A

What was the purpose of the Meselson-Stahl Experiment?

To determine which model of DNA Replication is accurate.

3 stages of DNA Replication.

Initiation, Elongation, Termination.

What happens during DNA replication initiation?

DNA strands separate

Small portion of RNA is annealed to the exposed strands to “prime” them for replications.

YES OR NO: Does DNA polymerase build a new strand of DNA by i ncorporating free nucleotides from the nucleoplasm.

YES

What unzips the DNA strands by its Hydrogen bonds?

Helicase

TRUE OR FALSE: At the end of each side of the replication bubble is a replication fork.

TRUE

How does RNA Prime a strand?

by annealing to DNA strand

What is needed for initiation in DNA replication?

needs existing 3’ end of a nucleotide with and -OH group, provided by the primer.

What does RNA Primase do?

synthesizes the primer and anneals it to the template strand.

TRUE OR FALSE: DNA polymerase cant addon DNA Nucleotides

FALSE: It can

In what direction do the new strands synthesize in DNA replicationg?

5’ → 3’

which end are the nucleotides added onto.

3’ end

TRUE OR FALSE: After being replicated, DNA Polymerase joins the backbones back together.

FALSE: Ligase joins the backbones.

In Termination, the two replication forks (____ _____) meet each other.

Circular Genome

two important characteristics of Replication.

1. Bi directionally (Replication proceeds in two directions)

2. Semi- discontinuity (Synthesis occurs continuously on one side, and discontinuously on the other

Elongation is semi-discountinuous; one strand builds continuously in one piece on the ______ _______, and discontinuously on the _________ ______.

Leading strand, lagging strand.

how is the Leading strand constructed.

Uses 3’ → 5’ template strand as a guide

built towards replication forks

Whats the construct of the lagging strand?

5’ → 3’ template

built in short fragments (Okazaki fragments)

constantly added RNA primers on the start of each fragment with RNA Primase.

types of errors that can occur are mispairing (Wrong nucleotide pairings), and slippage. They can be corrected with ________ and _______ _________ (about 130 enzymes that help).

Proofreading, Mismatch repair.

YES OR NO: Replication in prokaryotes is SLOWER than in eukaryotes.

NO

TRUE OR FALSE: Eukaryotic chromosomes have telomeres.

TRUE

What are Telomeres?

regions at the end of linear chromosomes

dont code for anything

to protect chromosomes from degredation

telomeres of lagging strand become shorter

most cells can undergo ~50 replications before telomeres become too short (Hayflick limit)

What does telomerase do?

prevents shortening of telomeres, and extends them so they never get to short. Only in embryonic cells, white blood cells, and gametes.

3 important properties of DNA replication.

• it is semi-conservative

• bi-directional

• semi-discontinuous

What did Chargaff do?

Found constant quantities of each nucleotide in DNA, and hydrolyzed DNA to quantitatively determine contents in nucleotides. (Percentages)

What did Franklin do?

Imrpoved X-ray crystallography, making them prouce photos of BDNA , which determined double-stranded DNA.

TRUE OR FALSE: Hershey and Chase studied crystallography.

FALSE: They studies bacteriphage genetics; which is a virus that attacks/infects bacteria.

TRUE OR FALSE: Watson and Crick published the double Helix model of DNA molecule.

TRUE

what is the central dogma?

Studied how RNA is synthesized from DNA, and Protein is synthesized from mRNA.

What did Meselon and Stahl work on?

Found DNA is made by copying old DNA

Daughter molecule = Parent strand + new synthesized strand

Prokaryotes and eukaryotes ______________________ in response to their changing environments.

Alter gene expression

What plays many roles in regulating gene expression?

RNA molecules

What is an operon?

a piece of DNA that includes the operator, promoter, and genes that they control.

a cluster of functionally related genes that can be under coordinated control by an on-off switch (a segment of DNA called the operator).

What does a repressible Operon do?

It is usually on; meaning the binding of the repressor to the operator shuts off transcription

TRUE OR FALSE: An inducible operon is usually off; a molecule called an induced inacrivates the repressor and turns OFF transcription

FALSE: turns ON transcription

what is a trp Operon?

a repressible operon is on and the genes from tryptophan synthesis are transcribed. When it is present, it binds to the trp repressor protein, which turns it off.

what is a lac operon?

The inducible operon needed for making the enzyme to metabolize lactose.

What are oncogenes and proto-oncogenes?

Oncogenes: cancer-causing genes

Proto-oncogenes: corresponding normal cellular genes that are needed for normal cell growth and division.

What do tumor-suppressor genes do?

Repair damaged DNA

Control cell adhesion

Inhibits cell cycle in cell signaling pathway

what is the triplet hypothesis?

a proposal where genetic code is read three nucleotides at a time.

what are the three characteristics of the genetic code?

• it is redundant (more than one codon can code for the same amino acid)

• it is continuous ( read in 3-letter series with spaces, punctuation, and overlaps

• it is partially universal (Almost all organisms build proteins with the same genetic code)

TRUE OR FALSE: stop codons are optional

FALSE: they are necessary in order to prevent mutations and more virus production.

what are the 3 different forms of RNA, produced from DNA templates, and that are all synthesized in the nucleus?

• Messeger RNA

• Ribosomal RNA

• Transfer RNA

Which genes strands are involved in transcription?

• anti-sense strand (template)

• sense - strands (coding strand)

In initiation phase, RNA Polymerase _____ to a promoted region on the DNA sequence, where the RNA polymerase will ______________________ a section of the double Helix.

binds, Unwind and open

YES OR NO: Promoter region is where translation begins

NO: where transcription begins

Which catalyzes faster; RNA polymerase catalyzing RNA synthesis or DNA Polymerase catalyzing DNA Synthesis?

RNA polymerase catalyzing RNA synthesis (No proofreading needed).

What is the difference between error in transcription and error in DNA replication?

Error in transcription: Error in one protein molecule

Error in DNA replication: Error in genetic make up of organism

What signals transcription to stop?

Polyadnylation Signal (AAUAAA)

what are the modifications needed for pre-mRNA before it leaves the nucleus?

Addition of 5’ cap (linkage of G nucleotides on 5’ end)

addition of 3’ poly-A-Tail (series of A nucleotides on 3’ end)

what are the three benefits of modification.

• facilitate transportation of mRNA

• Protect mRNA from degradation

• Enables ribosomes to bind to 5’ end and begin process of translation

what is RNA splicing?

where Introns (non coding segments not needed for protein synth.) are cut out for the exons (coding segments) of the pre mRNA to join together to form mature mRNA.

where will splicing occur?

by the snRNA (small nuclear RNA)

what are the 4 major components of translation machinery?

• mRNA

• tRNA

• Ribosomes

• Translation Factors (accessory proteins)

what is the look of tRNA?

• anti codon loop at the bottom (complementary to an mRNA codon)

• acceptor stem (single stranded region where amino acid attaches)

• hydroxide at 3’ end

• Phosphate at 5’ end

• stem loop structures

What composes ribosomes?

• rRNA

• proteins

• large and small sub-units

what happens in a Ribosome?

molecules that are involved in translation are assembled here (tRNA, mRNA, translation factors).

What are the three binding sites for tRNA.

• Peptide site (where the tRNA holds the growing peptide bond)

• Amino site (where tRNA enters the ribosome with the next amino acid)

• Exit site (where left over tRNA leaves ribosome after giving up peptide chain)

there are two groups of mutations?

• single-gene mutations

• chromosome mutations

how can single gene mutations be categorized?

• silent (change in a nucleotide base, but does not affect the amino acid)

• missense (change in the nucleotide base that affects amino acid)

• Nonsense (When the protein is shortened by an early stop codon)

What are some causes of chromosome mutations?

• deletion

• duplication

• inversion

• reciprocal translocation

TRUE OR FALSE: mutations are only induced.

FALSE: They can also be spontaneous.

the cause of spontaneous mutations can be caused by _______________________ by DNA polymerase during replication, ___________, or even the result of __________ molecular interactions.

Incorrect base pairing, transposition, normal.

what are the two types of induced mutations?

Physical mutagens (caused by UV rays or X-rays)

Chemical mutagens (Cigarette smoke or nitrites)

Draw the DNA replication bubble diagram

Draw RNA splicing diagram