Jake's bio Chapter 14

What is the link between genotype and phenotype

Proteins

Gene expression definition

process of DNA directing protein synthesis including transcription and translation

What did Archibald Garrod accomplish

genes dictate phenotypes through enzymes that catalyze specific chemical reactions

Metabolic pathway definition

Cells synthesizing and degrading molecules in a series of steps

What did Beadle and Tatum accomplish

studied mutations and how they are passed on

What is Beadle and Tatum’s hypothesis

one gene —> one polypeptide

What is the link between DNA and protein synthesis

RNA

What are the stages from DNA to protein

transcription

translation

Transcription definition

synthesis of RNA using information in DNA

What is the product of transcription

mRNA

translation definition

synthesis of a polypeptide using information in the mRNA

What are the sites of translaiton

ribosomes

In terms of order of steps, what is a major difference between bacteria and eukaryotes regarding transcription and translation

translation can occur before transcription has finished in bacteria

What separates the process of transcription and translation in eukaryotes

nuclear envelope

What process modified RNA transcripts

RNA processing

In eukaryotes, transcription occurs in __ and translation occurs in __

Nuclear enveolpe

cytoplasm

Where does translation and transcription occur in bacteria

cytoplasm

In eukaryotes, what happens to mRNA after it is transcribed

transported out of the nucleus

Primary transcript definition

initial RNA transcript from any gene prior to processing

Central dogma definition

Concept that cells are governed by a cellular chain of command

What is the template strand

orders the sequence of complementary nucleotides in an RNA transcript

During translation, what direction is the strand read

5’ —> 3’

How many possible codons are there

64

How many codons code for amino acids

61

How many codons code for stop signals

3

How is the genetic code nearly universal

Shared by the simplest bacteria and most complex plants and animals

What is the first stage of gene expression

transcirption

RNA polymerase function

assembles polynucleotides only in the 5’—> 3’ direction

What makes RNA polymerase different from DNA polymerases

Can start a chain without a primer

What enzyme starts the process of transcription

RNA polymerase

How does RNA polymerase get started with transcription

Pries DNA strands apart and joins together the complementary RNA nucleotides

Promoter function

DNA sequence where RNA polymerase attaches

Terminator function

DNA sequence that signals the end of transcription

Transcription unit definition

stretch of DNA that is transcribed

What are the three stages of transcription

1. Initiation

2. Elongation

3. Termination

What do promoters signal for

The starting point of transcription

What type of sequence is the TATA box

promoter

What is the function of the TATA box

form the initiation complex in eukaryotes

Transcription factors definition

mediate the binding of RNA polymerase and the initiation of transcription

Transcription initiation complex definition

Completed assembly of transcription factors and RNA polymerase II bound to a promoter

What happens to DNA as RNA polymerase moves along the strand

untwists the double helix 10-20 bases at a time

What is the rate of transcription in eukaryotes

40 nucleotides per second

What is often done to help speed up the process of transcription

A gene can be transcribed simultaneously by several RNA polymerases

What happens during the termination of transcription in bacteria

Polymerases stop at the end of the terminator and mRNA can be translated without further modification

What happens during the termination of transcription in eukaryotes

RNA polymerase II transcribed polyadenylation signal sequence; RNA transcript is released 10-30 nucleotides past this sequence

What happens during RNA processing in eukaryotes

Enzymes modify pre-mRNA before the genetic messages are dispatched to the cytoplasm

What happens to the primary transcript during RNA processing

both ends are altered

How is the 5’ end edited

modified G nucleotide cap

How is the 3’ end edited

poly-A tail

What are the functions of the edits at the end of mRNA

Facilitate the export of mRNA to the cytoplasm

Protect mRNA from hydrolytic enzymes

Helping ribosomes attach to the 5’ end

What happens during RNA splicing

large portions of the RNA molecule are removed and remaining portions reconnected

Introns definition

Noncoding regions

Exons definition

Usually translated into amino acid sequences

In general, what happens to mRNA during RNA splicing

Introns are cut out from the molecule and exons are joined together

Alternative RNA splicing definition

Many genes can give rise to two or more different polypeptides, depending on which segments are used as exons

What enzyme is in charge of RNA splicing

spliceosomes

What are spliceosomes consisted of

small RNAs

Ribozymes definition

RNA molecules that function as enzymes

What is the function of tRNA

Help translate an mRNA message into a protein and transfer amino acis to growing polypeptide in a ribosome

What is the general structure of a tRNA

Amino acid at one end. other end has nucleotide triplet that can base=pair with the complementary codon on mRNA

Roughly how long are tRNA molecules

80 nucleotides

Anticodon definition

Opposite/complementary sequence to the mRNA basepair

Steps for accurate translation

1. Correct match between a tRNA and an amino acid

2. Correct match between tRNA anticodon and mRNA codon

What enzyme is in charge of the correct match between a tRNA and amino acid

aminoacyl-tRNA synthetase

wobble definition

Allows incorrect third base in codon if the first two code for the same amino acid

What are ribosomes made out of

proteins and rRNA

When are the small and large subunits of a ribosome joined

Only when attached to an mRNA molecule

what are the sites of the ribosome called (left to right)

E

P

A

P site function

holds tRNA that carried the growing polypeptide chain

A site function

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

E site function

exit site, where discharged tRNAs leave the ribosome

What are the stages of translation

1. Initiation

2. Elongation

3. Termination

What do all three stages of translation require

protein factors

How is energy provided for translation

GTP hydrolysis

What is the initiation stage of translation

mRNA and a tRNA with the first amino acid + two ribosomal subunits join together

What is the most important function of the start codon

Establishes reading frame

What is the last component to join the translation initiation complex

Large ribosomal subunit

What brings together the translation initiation complex

Initiation factors

What happens during elongation of translation

Amino acids are added one by one to the previous amino acid at the C-terminus of the growing chain

What are the three steps to adding a polypeptide to the growing chain

1. Codon recogonition

2. peptide bond formation

3. Translocation

What is the direction translation takes place

5’ —> 3’

When does termination of translation occur

When stop codon reaches A site of the ribosome

What does each addition of an amino acid to a chain require

elongation factors

What type of protein enters the A site during termination of translation

Release factor

What does the release factor cause

addition of a water molecule instead of an amino acid which releases the polypeptide

What is the most common post-translational modification

folds

How can amino acids be modified post-translation

addition of sugars, lipids, phosphate groups, etc.

When is a polypeptide cleaved

two or more polypeptides coming together

Why must proteins undergo post-translational modificaitons

Need to happen to perform proper function

What are the two types of ribosomes (and where they are found

free (in cytosol)

Bound (in endoplasmic reticulum)

What is the function of free ribosomes

Synthesize proteins that function in the cytosol

What is the function of bound ribosomes

Make proteins of the endomembrane system and proteins that are secreted from the cell

Where does polypeptide synthesis always begin

cytosol

Where does polypeptide synthesis finish

Cytosol or endoplasmic reticulum

What is the function of the signal peptide

labels polypeptides destined for ER or secretion

What is the function of the signal-recognition particle

Escorts the signal peptide and its ribosome to a receptor in the ER membrane

In bacteria, transcription and translation can take place…

simultaneously

Why can’t eukaryotes undergo transcription and translation at the same time

The two processes happen at different locations

Mutations definition

changes in the genetic material of a cell

Point mutations definition

chemical changes in just one nucleotide pair of a gene