DNA - Structure, replication. Translation and Transcription

DNA

substance of hereditary information

DNA Structure

Double helix, nitrogenous base, deoxyribose sugar, phosphate group

Purines

A G

Pyrimidines

T C U

How many parallel strands

2 antiparallel strands, hydrogen bonds in between the strands

A and T

double bond

C and G

triple bond

Chromatin

DNA+Protein

Chromosome

condensed chromatin 

During DNA Replication, a cell uses a variety of proteins to…

create a new copy of its genome. it proceeds to use base pairing rules

Semi Conservative

One new One old Strand

DNA Replication in prokaryotes

Prokaryotic replication bubble, one direction

Eukaryotes have a lot of…

origins to not waste time

DNA Replication 1st step

DNA Helicase breaks the hydrogen bonds, unwinding the 2 strands

Second step

SSB code DNA around the fork to prevent rewinding

Third Step

DNA Polymerase adds nucleotides from 5—>3 direction

Leading strand

everything happens continously

Lagging strand 

made disconstinously, okazaki fragments starting with RNA primers 

4th step

DNA Polymerase removes the primers (starting point) and replaces them with DNA

5th step

DNA Ligase seals gaps between the fragments (phosphodiester bonds)

Prokaryotic chromosomes are circular…

one origin of replication

Proofreading and Repair

• Copying of DNA is remarkable in speed and accuracy 

• DNA Polymerases proofread their work 

• Mismatch repair: daughter strand repairs single base pair errors 

• Nucleotide Excision Repair: large errors repaired 

• Unrepaired errors —→ permanent mutation 

Central Dogma

DNA to RNA to Proteins

DNA to RNA is…

Transcription (tweaking)

RNA to Proteins is…

Translation (changing)

Transcription + Translation

Gene Expression

Express a gene —>

turn to protein (change which gene is expressed)

Gene Expression

copies of all genes of an organism are contained within all the cells of its body

• same set of genes may be expressed differently in life

• genes provide info that leads to production of polypeptides 

• Proteins: link between genotype and phenotype 

mRNA

almost identical to one of DNA strands (nontemplates)

• T replaced with U

Transcription

process of copying info from DNA to RNA

• only 1 strand of DNA is used as a template to create RNA 

• Nontranscribed- nontemplate 

first step of transcription

DNA is unwinded and RNA strand complementary to the DNA template is formed

second step of transcription

RNA synthesis follows the same base pairing rules as DNA except T and U

third step of transcription

RNA polymerase- enzyme that performs the polymerase reaction

Initiation

RNA Polymerase binds to DNA and unwinds it

• Promoter- tells enzyme where to start and which strand to use

Elongation

RNA Polymerase adding nucleotides to the mRNA in a 5—>3 direction, complimentary based pairing

Termination

occurs once RNA Polymerase reaches DNA template sequence, complex disassociates, RNA transcript released 

Prokaryotes

Transcription —> mRNA —> Translation

Eukaryotes

Translation —> premRNA —> RNA splicing —> mRNA —> Translation

RNA Splicing

coding regions exons interlinked with introns

• introns are removed and exons join together to produce the mRNA 

Translation-

process of converting info in mRNA into protein

Translation involves:

-ribosomes

-mRNA

-tRNA

-rRNA 

-amino acids

enzymes

energy

The genetic flow

flow of info from gene to protein is based on genetic code

Codon

triplet code

Characteristics of Genetic Code

1. Redundancy

2. Non ambiguity

3. Universal

Redundancy

more than 1 codon codes for same protein

Non ambiguity 

no codon specifies more than 1 amino acid 

universal

shared by everything

Reading frame

correcy grouping for polypeptide to form

tRNA

carries amino acids to the ribsome site of protein synthesis

Ribosomes

sites of translation

A site 

holds tRNA that carries the next amino acid to be added to the chain

P site

holds tRNA that carries the growing polypeptide chain

E site

exit site, discharged tRNA leave ribosomes

Stage 1 in Transcription

Initiation- ribosomes forms and initiator tRNA provides first amino acid

Stage 2 in Transcription

Elongation- tRNA molecules come in through A site, growinf a new polypeptide to A site 

Stage 3 in Transcription

Termination- occurs when stop codon is reached 

Polyribosomes

a string of ribosomes along an mRNA, multiple transit mRNA at the same time

• Allow a cell to make large quantities of protein quickly

Post translational modifications prepare proteins for their functions:

1. Proteolysis

2. Glycosylation

3. Phosphorylation

Translation in prokaryotic and eukaryotic cells:

• Pro- translation of mRNA can begin before transcription has finished

• Euk- nuclear envelope separates transcription from translation

Prokaryotes alter gene expression by:

• Regulation of transcription (nutrients, temp, pH)

Eukaryotes geen expression:

• Regulation of transcription

• Post transcriptional

• Translation

• Post translational

Cell differentiation

process by which cells become specialized in structure and function

• Cells become specialized by selectively expressing genes

Stem cells

are pluripotent, could replace damaged or diseased tissues and organs