Genetics Chapter 14

Exam 2

What is colinearity?

What is noncolinearity?

What should be said about the number of nucleotides in a gene and the number of amino acids?

The number of nucleotides in a gene should be proportional to the number of amino acids in the encoded protein

Which types of eukaryotes have which type of colinearity?

• Lower eukaryotes → colinear

• Higher eukaryotes → noncolinear

Which types of genes are and are not colinear with proteins?

Bacterial genes are colinear with proteins, while eukaryotic genes often are not

What does the concept of colinearity suggest?

A continuous sequence of nucleotides in DNA encodes a continuous sequence of amino acids in a protein

How was the noncolinearity of eukaryotic genes discovered?

Hybridizing DNA with the mRNA transcribed from it

What do eukaryotic genes contain?

Introns and Exons

What is the process of transcription regarding exons and introns?

Both are transcribed into RNA, but introns are later removed by RNA splicing

How common are introns in eukaryotic and bacterial genes?

Common in eukaryotic genes, uncommon in bacterial genes

• Numbers and sizes of introns vary from gene to gene

REVIEW slide 9, do we need to know this

What is the structure of a mature mRNA?

Contains a 5’ untranslated region (5’ UTR, or leader sequence), protein-coding region, and 3’ untranslated region

What did Brenner, Jacob, and Meselson demonstrate?

Ribosomes do not carry genetic information

What is the Shine-Delgarno sequence?

Protein-coding region; present in prokaryotes only

What steps are part of pre-mRNA processing?

5’ cap addition, polyA tail addition

What is a 5’ cap?

Nucleotide with 7-methylguanine; 5’-5’ bond is attached to the 5’ end of the RNA

What is the polyA tail?

Around 50-250 adenine nucleotides are added to the 3’ end of the mRNA; added through cleavage and polyadenylation

What is the purpose of RNA editing?

Alters nucleotide sequence of mRNA

What is the purpose of RNA splicing?

Removes noncoding introns from pre-mRNA, facilitates export of mRNA to cytoplasm, allows for multiple proteins to be produced through alternative splicing

What is the purpose of Internal RNA modifications

Influence splicing, mRNA degradation, and translation

What is the branch point in RNA splicing?

The adenine “A”: around 18-40 nucleotides upstream of the 3’-splicing site

What is the 5’ and 3’ consensus sequence

5’: GUA/GAGU : 5’ splice site

3’: CAGG

What is a spliceosome and where is it located?

Five RNA molecules + 300 proteins; located in the nucleus

What are the two steps of splicing nuclear pre-mRNA introns? Where do they take place?

1. 5’ end of the intron is cleaved from the upstream exon and attached to the branch point to form a lariat

2. The 3’ end of the intron is cleaved from the downstream exon and the ends of the two exons are spliced together

They take place within the spliceosome

How does the spliceosome assemble?

It assembles sequentially

Where do all three parts of nuclear organization take place?

Intron removal, mRNA processing, and transcription take place at the same site in the nucleus

What are the types of minor splicing?

Group 1 Introns and Group 2 introns

review slide 23 about minor splicing

What is significant about Group 1 and Group 2 introns?

They fold into characteristic secondary structures

What does alternative processing enable?

Enables exons to be spliced together in different combinations to yield mRNAs that encode different proteins

What does multiple 3’ cleave sites allow for?

Allows for pre-mRNA to be cleaved and polyadenylated at different sites

review slide 28

What is RNA editing?

a coding sequence is altered after transcription; carried out by guide RNAs

When is mature eukaryotic mRNA produced?

When pre-mRNA is transcribed and undergoes several types of processing

What is the structure of transfer RNA?

Rare modified RNA nucleotide bases (ribothymine, pseudouridine), common secondary structure (cloverleaf), and anticodon

Which cells process transfer RNAs

Both bacterial and eukaryotic cells

What is the structure of the ribosome?

Contains 2 subunits; large and small ribosome subunit

What is the purpose of RNA interference?

Limits the invasion of foreign genes and censors the expression of their own genes

How are small interfering RNAs and microRNAs produced

from double-stranded RNAs

Where are Piwi-interacting RNAs primarily found?

In germ cells of animals; they inhibit transposons

Where are CRISPR RNAs found?

In prokaryotes; they function in defense against foreign DNA, like bacteriophages and plasmids. They have been compared to the immune systems of vertebrates

What is the percentage that CRISPR-Cas systems are present in prokaryotes?

50% of bacterial species and 90% of archaea

What are long noncoding RNAs?

Long RNA molecules that do not encode proteins

Where are Enhancer RNAs transcribed from?

Transcribed from enhancers and also play a role in control of gene expression

What is the purpose of circular noncoding RNAs?

May serve as decoys for miRNAs