Day 10 Genetic Info Transfer

Pyrimidine

Cytosine, Uracil, Thymine (CUT)

Purine

Adenine, Guanine (AG)

What forms the backbone of a DNA strand?

Sugar-phosphate linkage formed by covalent bonds between nucleotides

Which specific carbons on the deoxyribose sugar bond with the phosphate groups?

The 5' (five prime) and 3’ (three prime) carbon

How do sugars and phosphates connect in a DNA strand's backbone pattern?

Each sugar attaches in a repetitive pattern to two phosphates

How many hydrogen bonds hold A–T and G–C pairs together?

AT: 2

CG: 3

Why is the origin of replication a short sequence rich in A and T?

A–T pairs have only 2 hydrogen bonds, so less energy is needed to separate the strands

Anti parallel

One side of helix runs in opposite direction of other

Which list correctly describes how RNA differs from DNA?

Single-stranded

Contains uracil

Contains ribose instead of deoxyribose

What are the genomes of cells and viruses made of?

Cells: DNA only

Viruses: DNA or RNA

What is the difference between genotype and phenotype?

Genotype is the sum of all genes (genetic makeup)

Phenotype is the expression of the genotype as traits

DNA replication is described as semiconservative. What does that mean?

Each daughter molecule has one original parent strand (template)

and one newly synthesized strand

Helicase

Breaks hydrogen bonds to unzip the DNA helix

What are the roles of DNA polymerase III and DNA polymerase I?

DNA polymerase III: Adds nucleotides to the new chain and proofreads

DNA polymerase I: Removes RNA primers, replaces them with DNA, and repairs mismatches

Leading strand from which to which prime?

The leading strand is synthesized continuously 5′→3′

How is the lagging strand made?

Made in short Okazaki fragments joined by DNA ligase

DNA ligase

Enzyme that joins DNA strands together by joining separate pieces of DNA together by forming covalent chemical bonds

What is the Central Dogma, and what are its exceptions?

DNA → RNA → protein

Exception: RNA viruses copy RNA to RNA

Retroviruses

Convert RNA to DNA

Which ribosome sizes and subunits are correct?

Bacterial, mitochondria, chloroplasts: 50S + 30S = 70S

Eukaryotic (nucleus): 60S + 40S = 80S

During translation initiation, what is the START codon,

and which tRNA anticodon first occupies the P site?

START codon: AUG

The initiator tRNA with the complementary anticodon UAC sits in the P site

Which codons terminate translation, and why does translation stop there?

UAA, UAG, UGA

There is no corresponding tRNA for them

A point mutation changes a codon so that it now codes for the SAME amino acid.

What type of mutation is this?

Silent mutation

What are the three components of a DNA nucleotide?

Phosphate, deoxyribose (5-carbon sugar), nitrogenous base

Match each RNA to its role. Which pairing is correct?

mRNA carries the instructions for making proteins

tRNA is the adaptor linking mRNA codons to amino acids

rRNA is a major structural component of the ribosome; has sequence complementary to regions of mRNA with which it can interact

Which of the following are regulatory RNAs?

MicroRNAs

Anti-sense RNAs

Riboswitches

Small interfering RNAs

What is a genome and where is it found?

The sum total of an organism's genetic material

Mostly in chromosomes

Also in plasmids and in eukaryotic mitochondria and chloroplasts

Compare bacterial and eukaryotic chromosomes

Bacterial: DNA condensed by histone-like proteins, usually one chromosome, extra genes on plasmids

Eukaryotic: DNA wound around histones in the nucleus, diploid or haploid, more linear

What is the purpose of DNA replication, and what is the purpose of transcription?

Replication: cell division

Transcription: making proteins to maintain cellular function

Which enzymes open up the DNA at the origin, and which proteins keep the strands apart?

Topoisomerases unwind the helix

& Helicases break the hydrogen bonds to separate the strands

Single-strand binding proteins keep them apart

What does primase do and why is it needed?

Synthesizes a short RNA primer that

DNA polymerase III needs to start adding nucleotides

What are the roles of DNA polymerase III and DNA polymerase I?

Pol III adds nucleotides and proofreads

Pol I removes RNA primers, replaces them with DNA, and repairs mismatches

Replication Steps

Topoisomerase unwinds

Helicase unzips

Single strand binding proteins hold strands apart

Primase adds RNA primer

Pol III extends

Pol I replaces primers

Ligase seals

What does RNA polymerase do during transcription?

Makes an RNA copy of the template strand of the DNA

Moving 5′→3′ as elongation continues

What is a codon?

A codon is three nucleotides specifying an amino acid

Wobble

Usually only the first two bases matter, so the third can vary without changing the amino acid

A DNA template strand reads 3′-TAC-5′.

What is the mRNA codon, the tRNA anticodon, and the amino acid?

mRNA Codon: AUG

tRNA Anticodon: UAC

Amino acid: Methionine (START)

mRNA 5′-AUG CCG CCG UAG-3′ is translated.

What peptide is made?

Met–Pro–Pro, then stop at UAG

Which describes the ribosome sites during elongation?

A site: incoming tRNA

P site: tRNA holding the growing chain

E site: empty tRNA exits

Which codons terminate translation and why does it stop?

UAA, UAG, UGA

There is no corresponding tRNA for them

What is a mutation and what is a wild type?

Mutation: any change in the nucleotide sequence of the genome

Wild type: an organism with the natural, nonmutated phenotype

What is the difference between spontaneous and induced mutations?

Spontaneous: random errors in replication

Induced: caused by exposure to mutagens such as UV light, X-rays, or chemicals like nitrous acid

Silent mutation

Base altered, amino acid unchanged, no effect

Missense mutation

Different amino acid is placed (may or may not function)

Nonsense

A normal codon becomes a stop codon

Frameshift

Insertion or deletion shifts the reading frame
and nearly always gives a nonfunctional protein

A single G is inserted into the middle of a gene.

What type of mutation is this, and what is the likely result?

Frameshift

Insertions and deletions of bases (not multiples of 3) shift every downstream codon

What is a single nucleotide polymorphism (SNP),

and why does it matter clinically?

A single altered nucleotide that is passed on genetically

Used as a marker for disease and key to personalized medicine

How do DNA polymerases repair mistakes during replication?

They detect mispaired bases

Uses 3′→5′ exonuclease activity to remove the incorrect nucleotide

Why can mutations be beneficial for bacteria, and how does this relate to antibiotic resistance?

Few create variants that survive when the environment changes

Antibiotic exposure selects for resistant mutants

When the environment changes (like antibiotic exposure), resistant mutants survive and reproduce

Which are examples of widespread antibiotic exposure that drive success of resistant mutants?

Unnecessary antibacterial soaps

Incomplete antibiotic courses

Antibiotics fed to livestock