Key Things to Know Chapter 17

nonsense mutations

change an amino acid codon into a stop codon; most lead to a nonfunctional protein

what are the stages of transcription

initiation, elongation, termination

missense mutations

still code for an amino acid, but not the correct amino acid

which molecule translates between nucleic acid language

tRNA

which process genetic information flows from mRNA to protein

translation

what does eukaryotes have to what for before beginning translation

wait for mRNA processing and transport of mRNE to the cytoplasm

what is an anticodon what structure does it complementary base pair with -figure 17.15

- A nucleotide triplet at one end of a tRNA molecule that base-pairs with a particular complementary codon on an mRNA molecule.

in initiation: TATA box

- a promoter that is crucial in forming the initiation complex in eukaryotes

what is the three binding sites for tRNA on a ribosome what is their purpose -figure 17.18

-*P site* holds the tRNA that carries the growing polypeptide chain -*A site* holds the tRNA that carries the next amino acid to be added to the chain -*E site* is the exit site, where discharged tRNAs leave the ribosome

how many codons are there how many are stop codons

-64 codons -3 stop codons

what is a mutagen

-A chemical or physical agent that interacts with DNA and can cause a mutation.

transcription unit (elongation)

A region of DNA that is transcribed into an RNA molecule.

what is a mutation

are changes in the genetic information of a cell

why can bacteria couple transcription and translation

because both occur in the cytoplasm

be able to explain what occur during mRNA processing -figure 17.13

-During RNA processing, both ends of the primary transcript are altered -Also, in most cases, certain interior sections of the molecule are cut out and the remaining parts spliced together

what are the differences between introns and eons is and which is removed during RNA splicing

-Introns: noncoding regions are called intervening sequence -Eons: because they are eventually expressed, usually translated into amino acid sequences -RNA splicing removes introns and joins exons, creating an mRNA molecule with a continuous coding sequence

what is RNA polymerase does it need a primer -figure 17.18

-RNA polymerase does not need any primer -RNA synthesis is catalyzed by RNA polymerase, which pries the DNA strands apart and joins together the RNA nucleotides

what is transcription what does it produce -figure 17.4

-Transcription is the synthesis of RNA using information in DNA - produces messenger RNA (mRNA)

what does the triplet code refer to -figure 17.5

-a series of nonoverlapping, three-nucleotide words

what does a single recognition particle (SRP) bind to what is its job

-binds to the signal peptide -SRP escorts the ribosome to a receptor protein built into the ER membrane

what can a polyribosome or polysome do for bacteria and eukaryotes -figure 17.23

-enable a cell to make many copies of a polypeptide very quickly

which has to go through RNA processing after transcription -prokaryotic or eukaryotic

-eukaryotic

what are the two populations of ribosomes are in a cell

-free ribosomes: in the cytosol -bound ribosomes: attached to the ER

silent mutation

-have no effect on the amino acid produced by a codon because of redundancy in the genetic code

what is a codon which direction is it read -figure 17.5

-mRNA base triplets -are read in the 5′ → 3′ direction -

what is a template strand as it refers to transcription -figure 17,5

-provides a template for ordering the sequence of complementary nucleotides in an RNA transcript -The template strand is always the same strandfor a given gene

single nucleotide pair substitutions figure 17.27

-replaces one nucleotide and its partner with another pair of nucleotides

what are the three stages of translation what are the key events that occur during each -figure 17.19 figure 17.20 17.21

. Initiation: begins with mRNA associates with a small ribosomal subunit. the amino acid methionine is attached to the region of the tRNA opposite the anticodon 2. Elongation: each successive Condon is read by the tRNA molecule that Bring the corresponding amino acid. amino acids are linked by peptide bonds formed by catalytic components 3. termination: occurs when a stop Condon is encountered. Protein folding and final touches occur after. Protein synthesis occurs

which end are nucleotides added to the end of growing RNA molecules

3'

polyadenylation signal sequence

AAUAAA RNA transcript is released 10-35 nucleotides past this polyadenylation sequence -used in eukaryotes

what is primary transcript

An initial RNA transcript from any gene; also called pre-mRNA when transcribed from a protein-coding gene.

what is gene expression? what are the two stages

Gene expression, the process by which DNA directs protein synthesis, includes two stages: transcription and translation

frameshift mutation

Insertion or deletion of nucleotides may alter the reading frame -generally more disastrous effect

in initiation what is the promoter -figure 17.19

Promoters signal the transcription start point and usually extend several dozen nucleotide pairs upstream of the start point

explain the transcription process

RNA synthesis is catalyzed by RNA polymerase, which pries the DNA strands apart and joins together the RNA nucleotides The RNA is complementary to the DNA template strand RNA polymerase does not need any primer RNA synthesis follows the same base-pairing rules as DNA, except that uracil substitutes for thymine

what are the three types of RNA used in translation are and what the role of each one is

Ribosomal RNA: RNA molecules that, together with proteins, make up ribosomes; the most abundant type of RNA. -Messenger RNA:A type of RNA, synthesized using a DNA template, that attaches to ribosomes in the cytoplasm and specifies the primary structure of a protein. (In eukaryotes, the primary RNA transcript must undergo RNA processing to become mRNA.) - transfer RNA: An RNA molecule that functions as a translator between nucleic acid and protein languages by picking up a specific amino acid and carrying it to the ribosome, where the tRNA recognizes the appropriate codon in the mRNA.

what determines whether a ribosome becomes attached to the endoplasmic reticulum or stays free in the cytoplasm -figure 17.22

Ribosomes are identical and can switch from free to bound

what does ribozymes

Ribozymes are catalytic RNA molecules that function as enzymes and can splice RNA

what does alternative RNA splicing

Some genes can encode more than one kind of polypeptide, depending on which segments are treated as exons during splicing

what does spliceosomes

Spliceosomes consist of a variety of proteins and several small RNAs that recognize the splice sites

transcription initiation complex

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

what does the one-gene-one polypeptide hypothesis state

The hypothesis states that the function of a gene is to dictate production of a specific enzyme

what is translation where does it occur

Translation is the synthesis of a polypeptide, using information in the mRNA Ribosomes are the sites of translation

uracil

a nitrogen-containing base found in RNA (but not in DNA) and derived from pyrimidine -binds with adenine

terminator (termination)

a sequence of nucleotides in DNA that marks the end of a gene and signals RNA polymerase to release the newly made RNA molecule and detach from the DNA. -used in prokaryotes

nucleotide pair insertion or deletion

are additions or losses of nucleotide pairs in a gene

point mutation -figure 17.16

are changes in just one nucleotide pair of a gene

Some mutations may be susceptible to certain environmental conditions

example: Siamese cats have a temperature-sensitive mutation in an enzyme for making dark pigment which doesn't work at higher temperatures

what does the enzyme aminoacyl tRNA does

matches the tRNA to the correct amino acid

transcription factors

mediate the binding of RNA polymerase and the initiation of transcription

what does it mean when saying the genetic code is redundant -figure 17,6

more than one codon may specify a particular amino acid

what is meant by the genetic code is nearly universal -figure 17.7

shared by the simplest bacteria and the most complex animals

in initiation: start point

the nucleotide position on the promoter where RNA polymerase begins synthesis of RNA.

how many nucleotides correspond to each amino acid

three