Gene Expression: from gene to protein

Gene expression

the process where DNA directs protein synthesis, transcription + translation

Protein Synthesis

the process where cells generate new proteins, involving the translation of genetic information contained in mRNA into a specific sequence of amino acids to form a protein.

Central dogma of molecular biology

describes the flow of information from DNA —> mRNA —> protein

Genes specify the sequence of mRNA which then specify the sequence of proteins

Synthesis

the process of combining different components or elements to form a coherent whole or a new entity.

Transcription

first phase in gene expression

the synthesis of mRNA using information in DNA

Translation

Synthesis of polypeptides using information in the mRNA

RNA regarding transcription and translation

The bridge between genes and the protein that they code

Ribosomes

site of translation

Transciption and translation in eucaryotic cells

nuclear envelope separates transcription from translation, they are not coupled- they don’t happen at the same time

RNA processing

where eukaryotic RNA transcripts are modified to make mRNA

Transcription and translation in bacteria (prokaryotes)

Translation of mRNA can begin before transcription has finished

transcription + translation are couples (happen at the same time)

No pre-mRNA/ RNA processing

Amino acids that code for nucleotide bases in DNA

adenine, guanine, cytosine, and thymine

triplets code

a series of non-overlapping, three nucleotide words that are responsible for the flow of information from gene to protein

The words translate into amino acids forming polypeptide chains

What happens during trascription

One of the two DNA strands (template strand) provides a template for ordering the sequence of complementary nucleotides in RNA transcript

RNA strand is complementary to DNA template strand and uses U instead of T

What happens during translation

mRNA codons are read from 5’ —> 3’

Each codon specifies to an amino acid to be placed in its corresponding position on the polypeptide

Stop codons

UAA, UGA, UAG

Start codon

AUG

Genetic code is redundant

Multiple codons may equal the same amino acid

UUU, UUC = Phe

can one codon code for multiple amino acids

no

what does it mean that genetic code is universal

Shard by the simplest od bacteria to the most complex animals

Non-Univeral genetic code

Mitochondria and Protists (paramecium)

RNA polymerase in transcription

Catalyze RNA synthesis, pulls DNA strands apart and joins them together with RNA nucleotides

does not require a promoter

where the DNA sequence that RNA polymerase attaches to

promoter

Transcription unit

the stretch of DNA that is transcribed

Three stages of transcription

initiation, elongation, termination

What happens at the start of initiation of transcription

Promotor signals transcriptional start point and extend several dozen nucleotide pairs from the start point

TATA box

A promoter that states the initiation complex in eukaryotic DNA

Binds to TATA binding protein, causing a bend in the DNA molecule

Determines the start point transcription

5’ → TATAAA→ 3’

Not in bacteria DNA

transcription factors

Mediates the binding of RNA polymerase and the initiation of transcription

transcription initiation complex

completed assembly of transcription factors and RNA polymerase 2 bound to a promoter

Elongation of the RNA strand

RNA polymerase moves along DNA untwisting the double helix 10-20 bases at a time

Nucleotides are added to the 3’ end of the RNA molecule

Can a gene be transcribed simultaneously by several RNA polymerases

Yes

Termination of transcription in bacteria

Polymerase stopes transcription at the end of the terminator and the mRNA can be translated without further modification

Termination of transcription in eukaryotes

RNA polymerase 2 transcribes the polyadenylation signal sequence; the RNA transcript is released 10-35 nucleotides past the is polyadenylation (poly A) sequence

pre-mRNA

initial transcript of a gene that undergoes processing to become mature mRNA, which includes splicing, capping, and polyadenylation.

What happens to the primary transcript during RNA peocessing

modification allowing it to become mature mRNA

Capping

Poly A tail

Splicing

capping in RNA processing

the addition of a modified guanine nucleotide to the 5' end of the primary transcript, which protects the RNA from degradation and facilitates ribosome binding during translation.

polyadenylation in RNA processing

the addition of a poly(A) tail, a long stretch of adenine nucleotides, to the 3' end of the transcript, enhancing its stability and aiding in its export from the nucleus.

splicing in RNA processing

Splicing is the process of removing non-coding regions (introns) from the primary transcript and joining the coding regions (exons) together, forming the mature mRNA that can be translated into proteins.

Introns and Exons

Introns: noncoding regions

Exons: expresed region of RNA, usually translated into amino acid sequences

Function of introns

transcribed into pre-mRNA but are removed during RNA splicing. regulate genes and alternative splicing, allowing for the production of multiple proteins from a single gene.

exon shuffling

coding regions of genes, are rearranged or recombined to create new genes or protein variants. This mechanism contributes to genetic diversity and the evolution of new

What happened to the ends of pre-mRNA while its being modified in the nucleus

5’ end receives a modified 5’ cap (Guanine)

3’ end gets a poly-A tail

Function of modified mRNA ends

Facilitate the export of mRNA to the cytoplasm

Protects mRNA from hydrolytic enzymes

Help ribosomes attach to the 5’ end of mRNA

RNA cutting and splicing

Removes introns and joins exons creating an mRNA molecule with a continuous coding sequence

Catalyze

to make a chemical reaction happen or happen more quickly by acting as a catalyst

Catalyst

a protein that speeds up biochemical reactions within cells without being consumed in the process, allowing life processes to occur efficiently

Spliceosomes

Responsible for the accurate cutting of introns

Catalyze the splicing reaction

Consist of several small nuclear ribonucleoprotein (snRNPs) or snurps that recognized splice sites

5’ splice is bound by U1 snRNA

3’ splice site is bound by U2 auxiliary factor

Ribozymes

an RNA molecule capable of acting as an enzyme.

What properties allow RNA to function as an enzyme

1. Can form a 3D structure because of its ability to base-pair with itself

2. contains functional groups that participate in catalysis

3. Hydrogen bonds with other nucleic acid molecules

three binding sites of tRNA

Types of RNA

Ribosome RNA (structure)

Ribosomal protein- part of the ribosomes → structural (nothing to do with the protein making)

Pre-mRNA- genetic code → affects proteins

mRNA- processed, no introns

tRNA- bring aa to ribosomes for protein synthesis

RNA Primer- replication

snRNP- small proteins and RNAs → stabilized introns for cutting, exon junction

Mutations

Missense mutation

Sickle cell

point mutation

Frame mutation

insertion and deletion (serous mutation)

Silent mutation

chnage in condon has no effect

Nonsense mutation