Molecular Basis of Inheritance

DNA

the substance of inheritance, is the most celebrated molecule of our time. Hereditary information is encoded in DNA and reproduced in all cells of the body

DNA program

m directs the development of biochemical, anatomical, physiological, and (to some extent) behavioral traits

Fredrick Griffith

The discovery of the genetic role of DNA began with research by (----) in 1928

Erwin Charga

reported that DNA composition varies from one species to the next and the number of A and T bases are equal and the number of G and C bases are equal

Nucleotides

are the building blocks of DNA

Thymine & Adenine & Cytosine & Guanine

Four Nitrogenous Bases

double helix

shape of the DNA

A – T (U) & G – C

Complementary base pairing

antiparallel

strands of a DNA double helix are said to be "-------" because the have the same chemical structure, but are opposite in direction

acts as a template

Since two strands of DNA are complementary, each strand (--------) for building a new strand in replication

DNA replication

the parent molecule unwinds, and two new daughter strands are built based on base-pairing rules

Semiconservative Model

model of replication that predicts that when a double helix replicates, each daughter molecule will have one old strand (derives or “conserves” from the parent molecule) and one newly made strand

origins of replication

Replication begins at particular sites called

Bubble

the two DNA strands are separated, opening up a replication “---------”

replication fork,

At the end of each replication bubble is a “--------” a Y-shaped region where new DNA strands are elongating

Helicases

are enzymes that untwist the double helix at the replication forks

Single-strand binding proteins

bind to and stabilize single-stranded DNA

Topoisomerase

corrects “overwinding” ahead of replication forks by breaking, swiveling, and rejoining DNA strands

short RNA primer

The initial nucleotide strand is

primase

An enzyme that can start from scratch and adds nucleotides one at a time using the parental DNA as a template

DNA polymerases

Enzymes that catalyze the elongation of new DNA

5’ to 3’ direction

DNA polymerases add nucleotides only to the free 3-prime end of a growing strand; therefore, a new DNA strand can elongate only in the (--------)

leading strand

Along one template strand of DNA, the DNA polymerases synthesizes a -------- continuously, moving toward the replication fork

lagging strand

To elongate the other new strand, called the (-------), DNA polymerase must work in the direction away from the replication fork

Okazaki fragments

The lagging strand is synthesized as a series of segments called (---------), which are joined together by DNA ligase

mismatch repair

In (--------) of DNA, repair enzymes correct error in base pairing

RNA

is the bridge between genes and the proteins for which they code

Transcription

is the synthesis of RNA using information in DNA

Translation

is the synthesis of a polypeptide, using information in the mRNA

Transcription

produces messenger RNA (mRNA)

Ribosomes

are the sites of translation

primary transcript

A (-----) is the initial RNA transcript from any gene prior to processing

DNA -> RNA -> PROTEIN

The central dogma is the concept that cells are governed by a cellular chain of command:

RNA polymerases

RNA synthesis is catalyzed by (---------) which pries the DNA strands apart and join together the RNA nucleotides

uracil , thymine

RNA synthesis follows the same base-pairing rules as DNA, except that (--------) substitute for (----------)

Initiation, Elongation, & Termination

The three stages of transcriptions

modify pre-mRNA (RNA processing)

Enzymes in the eukaryotic nucleus (-----------) before the genetic messages are dispatched to the cytoplasm

The 5’ end receives a modified nucleotide 5’ cap & The 3’ end gets a poly-A tail

Each end of a pre-mRNA molecule is modified in a particular way:

spliceosomes

RNA splicing is carried out by

codons

The mRNA base triplets, called (-------), are read in the 5’ to 3’ direction

amino acid (one of 20)

Each codon specifies the (----------) to be placed at the corresponding position along a polypeptide

Translation

is a complex process in terms of its biochemistry and mechanics

transfer RNA (tRNA)

A cell translates an mRNA message into protein with the help of

amino acids , polypeptide

tRNAs transfer (--------) to the growing (--------) in a ribosome

amino acid & anticodon

each molecule of tRNA carries a specific (----------) & (-----------) on each of its two ends

two steps

accurate translation requires how many steps?

First step of accurate translation

Correct match between a tRNA and an amino acid, done by the enzyme aminoacyl-tRNA synthetase

second step of accurate translation

A correct match between the tRNA anticodon and an mRNA codon

three sites

how many binding sites does ribosomes have for tRNA

P site

this site Holds the tRNA that carries the growing polypeptide chain

A site

this site Holds the tRNA that carries the next amino acid to be added to the chain

E site

Is the exit side, where discharged tRNAs leave thee ribosome

Initiation, Elongation & Termination

the stages of translation

Initiation

stage of translation where it brings together mRNA, a tRNA with the first amino acid, and the two ribosomal subunits

Initiation

stage of translation where this happens : First, a small ribosomal subunit binds with mRNA and a special initiator tRNA • Then the small subunit moves along the mRNA until it reaches the start codon (AUG)

Initiation factors

proteins called (---------) bring in the large subunit that completes the translation initiation complex

Elongation

stage of translation where : ribosome ready for aminoacyl tRNA , codon recognition , peptide bond formation and translocation

Termination

stage of translation where it occurs when a stop codon in the mRNA reaches the A site of the ribosome

Mutations

are changes in the genetic material of a cell or virus

Point mutations

are chemical changes in just one base pair of a gene

abnormal protein

The change of a single nucleotide in a DNA template strand can lead to the production of an

genetic disorder or hereditary disease

If mutation has an adverse effect on the phenotype of the organism the condition is referred to as a

nucleotide-pair substitution

A (-----------) replaces one nucleotide and its partner with another pair of nucleotides

Silent mutations

they have no effect on the amino acid produced by a codon because of redundancy in the genetic cod

Missense mutations

these mutations still code for an amino acid, but not the correct amino acid

Nonsense mutations

these mutations change an amino acid codon into a stop codon, nearly always leading to a nonfunctional protein

Insertions

are additions s of nucleotide pairs in a gene

deletions

are losses of nucleotide pairs in a gene

frameshift mutation

Insertion or deletion of nucleotides may alter the reading frame, producing a

frameshift mutation

These mutations have a disastrous effect on the resulting protein more often than substitutions do

Conservative Model

this type of model tells us that would produce two helices, and among them, one contains entirely old DNA while the other contains entirely new DNA

Dispersive Model

this type of model tells us that every round of replication would result in hybrids, or DNA double helices that are part original DNA and part new DNA

Conservative, Semi conservative, & Dispersion Models

three models of DNA replication