Biochem 3-6 Translation

Front 1

rRNAs are members of the ______ sequence class.

Back 1

intermediate

Front 2

Oscar Miller feathers

Back 2

multiple transcripts from each gene are produced simultaneously... they like the barbs of a feather and Oscar Miller discovered 'em, so there you go.

Front 3

The _____ is the region of a nucleus where ribosomes are produced.

Back 3

nucleolus; not membrane bound
-region where multiple rRNA transcripts are expressed from multiple genes, with protein binding each transcript. With so many ribosomes “pouring out,” the region looks dark under a light microscope.

Front 4

Each gene encodes ___ rRNAs. They are all transcribed by Pol __ as one large RNA molecule, known as Pre-rRNA. The intervening sequences are then cleaved away, leaving the three rRNAs; 28S, 18S, and 5.8S.

Back 4

3, Pol I

Front 5

What 3 rRNAs are left after intervening sequences are cleaved away?

Back 5

-28S
-18S
-5.8S

Front 6

A forth rRNA is transcribed from separate _____ genes. These are transcribed by Pol ___, the polymerase that produces tRNAs.

Back 6

5S rRNA, Pol III

Front 7

ribonucleoprotieins

Back 7

proteins that assemble around the rRNA to form the large and small subunits of ribosomes. Therefore, ribosomes are composed of RNA and protein.

Front 8

What makes up the large ribosomal subunit? What about the small ribosomal subunit?

Back 8

-large: 5S, 5.8S, 28S + ribonucleoproteins
-small- 18S + ribonucleoproteins

Front 9

Each rRNA gene is polycistronic,meaning is encodes multiple _____.

Back 9

rRNA transcripts

Front 10

Polycistronic rRNAs are transcried as intact units call _____.

Back 10

pre-rRNAs

Front 11

tRNA structure

Back 11

The primary transcripts of tRNAs undergo extensive post transcriptional modification. This includes intron splicing, nucleotide addition, methylation, and modifications to produce unusual nucleotides such as dihydrouridine (D), pseudouridine (ψ) and ribothymidine (T).

Front 12

folding

Back 12

Internal annealing folds tRNAs into “clover leaves.” The D and TψCG loops also fold back on each other to generate L shaped structures

Front 13

Anticodon

Back 13

A nucleotide triplet at the apex of the tRNA, which is complimentary to a specific codon of mRNA. In the ribosome, an anticodon binds a codon. This is how codons specify amino acids

Front 14

Unique properties of RNA polymerase I and Pol III promoters

Back 14

Unlike Pol II, promoters for rRNA and tRNA lack TATA boxes. Surprisingly, TBP is still a component of their initiation complexes.

Front 15

Pol III

Back 15

Pol III promoters are within their genes. Moreover, their DNA strands fold back on themselves to form internal base pairs. Note, the small RNAs transcribed by Pol III are characterized by internal annealing. Therefore, Pol III recognizes the same tertiary structure in the DNA that exists in the RNA.

Front 16

nuclear pore complexes

Back 16

mRNA, tRNA and ribosomes are all produced in the nucleus, but translation occurs in the cytoplasm, so all three components must be transported out. Other factors, such as DNA, transcription factors, and RNA polymerase must be imported into the nucleus. This occurs through channels embedded in the nuclear envelope, known as nuclear pore complexes. These are huge structures, 16 times larger than ribosomes, composed of 30 different proteins known as nucleoporins. The selective transport of factors into or out of the nucleus is mediated by proteins such as importins and exportins, which bind specific factors, and shuttle them through the nuclear pore complex.

Front 17

tRNA charging

Back 17

After tRNAs reach the cytoplasm, there is one more step before they are ready to be used for translation. They must be bound with their specific amino acids. This is often referred to as tRNA loading or charging. An enzyme called an aminoacyl-tRNA synthetase binds the 3' OH of the tRNA with the carboxyl group of its amino acid. The reaction requires an ATP for energy.

Front 18

degeneracy of the genetic code

Back 18

there are over 50 tRNAs, but there are only 20 amino acids. So a given amino acid can be bound to several tRNAs. However, each tRNA is only bound to one amino acid, and will only bind one codon. Multiple tRNAs for a given amino acid contributes to the degeneracy of the genetic code.