Protein synthesis

DNA characteristics

Sugar is deoxyribose, double helix, stays in the nucleus, nitrogenous basese A, T, C, G

RNA charecteristics

Sugar is ribose, single stranded, can leave the nucleus, nitrogenous bases A, U, C, G, has messenger RNA, transfer RNA, ribosomal RNA.

Flow of genetic information in transcription

DNA to mRNA. DNA provides a template for the synthesis of a complementary RNA strand

Translation flow of genetic informaiton

mRNA to protein. Informaiton contained in the order of nucleotides in mRNA determines amino acid sequence of polypeptide

Where does translation occurr

ribosomes

Prokaryote charecteristics of transcription and translaiton

they are coupled (happen at the same time), and ribosomes attach to the leading end of mRNA molecule while transcription is still in progress

eukaryotic charecteristics of transcription and translation

transcription occurs in the nucleus and translation occurs at ribosomes, before the primary transcript can leave the nucleus, it is modified during RNA processing.

Moleculer chain of command in a cell

DNA → RNA → protein

The genetic code is ____ but not ____

redundant, ambiguous

What does it mean that the genetic code is universal

it is shared by all organisms, so genes can be transcribed and translated after transplant from one species to another

RNA polymerase

separates the DNA strands at the appropriate point and bonds the RNA nucleotides as they base pair along the DNA template

What direction are new RNA molecules synthesized

5 to 3

What sequence of nucleotides marks where gene transcription starts

promoter, which RNA polymerase attaches onto “upstream” of the information contained in the gene, the transcription unit

Terminator function

signals the end of transcription

TATA box

eukaryotic promoter DNA

Transcription factors

recognize the promoter region and bind to the promoter so RNA polymerase can bind and create a transcription initiation complex

Elongation

RNA polymerase unzips portions of the DNA so a mRNA molecule can copy the information. RNA polymerase adds nucleotides to the 3’ end of the growing RNA strand.

Can multiple RNA polymerases transcribe one gene

yes, this makes more proteins ultimately

What happens when a terminator sequence is transcribed in prokaryotes

RNA polymerase stops transcription right at the end of the terminator, and both RNA and DNA is released.

In eukaryotes what happens when a terminator sequence is trancribed in prokaryotes

The polymerase continues for hundreds of nucleotides past the terminator sequence. At a point about 10-35 nucleotides past this sequence, the pre-mRNA is cut from the enzyme

Function of 5’ cap and Poly A Tail at the ends of mRNA

protects from hydrolytic (causing hydrolysis) enzymes and functions as a attach here signal for ribosomes

What is the poly(A) tail and what is its additional function beyond inhibiting hydrolysis and facilitating ribosome attachment

50-250 adenine nucleotides at the 3’ end. Facilitates export of mRNA from the nucleus

RNA splicing

Removal of a large portion of a RNA molecule (Introns) for a continuous coding sequence to bring exons together.

What drives RNA splicing

spliceosome

How are splicesomes formed

Pre-mRNA and snRNPs combine to form splicesomes

Alternate RNA splicing

gives rise to two or more different polypeptides, depending on which segments are treated as exons. EX: creates stomach proteins when needed and treated different exons as introns if it needs muscle proteins.

Translation

the cell interprets genetic code and builds a protein accordingly

Transfer RNA (tRNA)

transfers amino acids from the cytoplasms pool to a ribosome, then the ribosome adds each amino acid carried by tRNA to the growing end of the polypeptide chain

each tRNA arriving at the ribosome carries a specific ___ at one end and a specific nucleotide triplet, ___, at the other

amino acid, anticodon

What do anticodons pair with

complementary codon on the mRNA

can tRNA be used repeatedly

yes once it reaches the cytoplasm to pick up designated amino acids in the cytosol, deposit the amino acid at the ribosome, and return to the cytosol to pick up another copy of that amino acid

tRNA molecule charecteristics

strand of about 80 nucleotides that fold back on itsef to form a three dimensional structure with a loop containing the anticodon and a attachment site at the 3’ end for a amino acid

free floating ribosome function

make proteins that stay in the cell

Rough er ribosome function

make proteins destined for ER or Golgi

wobble

can pair not normal base pair rules

what two subunits are ribosomes composed of

large and small subunits composed of ribosomal RNA and protein

A site

carries the tRNA with the next amino acid

P site

holds the tRNA carrying the growing polypeptide chain

E site

discharged tRNAs exit here

Since both initiation and chain elongation require energy, how do they get it

hydrolysis of GTP

Initiation translation

brings together mRNA, a tRNA with the first amino acid, and two ribosomal subunits. Starts with start codon in ribosomal subunit in P site.

Translation elongation

series of three step cycles as each amino acid is added to the proceeding one.

1st step of elongation translation

During codon recognition, an elongation factor assists hydrogen bonding between the mRNA codon under the A site with the corresponding anticodon of tRNA carrying the appropriate amino acid requiring hydrolysis of GTP.

2nd step of elongation translation

During peptide bond formation, an rRNA molecule catalyzes the formation of a peptide bond betweeen the polypeptide in the P site with the new amino acid in the A site. TLDR: peptide bond forms on the p site, moves to the A site once it gains another amino acid on the P site and becomes longer each time.

3rd step of elongation translation

translocaton - the ribosome moves the tRNA with the attached polypeptide from the A site to the P site. This frees up the codon on the A site and the tRNA on the P site before is moved to the E site and leaves the ribosome. All fueled by hydrolysis of GTP.

Translation termination

occurs when one of the three stop codons reaches the A site. A release factor binds to the stop codon and hydrolyzes the bond between the polypeptide and its tRNA in the P site. This frees the polypeptide and the translation complex disassembles

Can polyribosomes trail along the same mRNA

yes, this makes translation more efficient

Mutations

changes in the genetic material of a cell.

Point mutation

chemical changei n just one base pair of a gene

Base pair substitution

replacement of a pair of complementary nucleotides with another pair

What happens if a point mutation occurs in gametes

They will be passed on to future generations

what is sickle cell disease a example of

point mutation

silent mutations

alterations of nucleotides still code for the same amino acids due to redundancy

Insertion mutations

addition of a base

Deletion mutation

deletion of one base

frameshift mutation

mutations that affect the way the original base pairs were read by insertion or deletion

Missense mutations

those that still code for an amino acid but change indicated amino acid

Nonsense mutations

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