Genetic Expression: BISC120 Units 17.1-17.5

proteins are the…

links between genotype and phenotype

What is gene expression

the process by which DNA directs protein synthesis. This includes 2 stages: transcription and translation

When can translation begin for prokaryotes?

before transcription has finished

What is the difference between translation in prokaryotes and eukaryotes?

• in prokaryotes translation of mRNA can begin before transcription has finished (transcription and translation can happen simultaneously because there is nothing separating where the processes happen)

• In eukaryotes translation happens within the nuclear envelope

Eukaryotic RNA transcripts are modified through…

RNA processing to yield the finished mRNA

What is the Central Dogma?

the concept that cells are governed by a cellular chain of command (DNA→ RNA→ Protein)

What does transcription do?

synthesize mRNA from DNA (copy a DNA segment into messenger RNA)

What are the three stages of transcription?

1. Initiation

2. Elongation

3. Termination

What is a template strand?

the strand of DNA that provides a template for ordering the sequence of complementary nucleotides in an RNA transcript

non-template strand aka…

coding strand

what are promoters

DNA regions that initiate the transcription of a gene

• signal the transcription start point

• eukaryotes have a promoter called a TATA box

what are transcription factors?

proteins that help guide the binding of RNA polymerase

what is RNA polymerase?

• an enzyme that catalyzes the synthesis of RNA from DNA template

• a specialized protein

what does RNA polymerase do?

it unwinds the double helix 10-20 nucleotides at a time

how is a template strand read?

3’-5’

how is a RNA strand built?

5’-3’ nucleotides are added to the 3’ end of the growing RNA molecule

what is the last step of RNA synthesis?

the RNA strand is released from the RNA polymerase, which is signaled by the terminator

what are the steps involved in transcription?

1. initiation - Promoter initiates the start of transcription, transcription factors guide the construction of RNA polymerase

2. elongation - RNA polymerase untwists the DNA (separates the template and non-template strands), RNA strand is being built on the template DNA

3. Termination - RNA strand is released from the RNA polymerase

What do ribosomes do?

take info from DNA to make proteins (ribosomes build protein in the cytosol and outside the endoplasmic reticulum)

how are proteins constructed?

through nucleotide sequences of genes in DNA (code for constructing a protein)

What does translation involve?

the conversion of the nucleic acid language to the polypeptide (protein language)

• takes in this language through a triplet code (3 nucleotides), which are organized and stored in codons

what is the genetic code?

the set of rules that dictates the amino acid translations of each of the mRNA nucleotide triplets

what are the three phases of translation?

1. initiation- the small ribosomal subunit binds with mRNA and a special initiator tRNA, the special initiator tRNA carries the amino acid methionine, then the unit moves along the mRNA until it reaches the start codon

2. Elongation- translation proceeds along the mRNA in a 5’-3’ fashion

3. Termination- a tRNA with a complementary anticodon pairs with each codon, elongation continues until a stop codon is reached

point mutations are…

changes in just one nucleotide pair of a gene

nucleotide-pair substitutions replace..

one nucleotide and its partner with another pair of nucleotides

missense mutations are when…

the mutation codes for an amino acid, just not the correct one

Nonsense mutations are when a..

change causes an amino acid codon to turn into a stop codon

a silent mutation is..

when the mutation that occurred has no effect on the amino acid produced (more than one codon for each amino acid)