biology exam 4

Sequences of nucleotides

The information content of genes is in the form of specific

Synthesis of proteins

The DNA inherited by an organism leads to specific traits by dictating the__

Genotype and phenotype

Proteins are linked between

Gene expression*

The process by which DNA directs protein synthesis

transcription and translation

the two stages of gene expression/getting from DNA to protein requires

one gene-one protein

som proteins are not enzymes so researchers later revises the one gene-one enzyme to__

polypeptides

many proteins are composed of several ____ each has its own gene

RNA

the bridge between DNA and protein synthesis

RNA is usually

single-stranded

transcription

is the synthesis of RNA using information In DNA/produces messenger RNA (mRNA)

ribose sugar

RNA has a ____ and the base uracil rather than thymine

translation

the synthesis of a polypeptide using information on the mRNA

ribosome

the sites of translation

in prokaryotes

translation of mRNA can begin before transcription has finished

in eukaryotes

the nuclear envelope separates transcription from translation

eukaryotic

RNA transcripts are modified through RNA processing to yield the finishing mRNA

nucleus

eukaryotic mRNA must be transported out of the___ to be translated

primary transcript

the initial RNA transcript from t\why gene prior to processing

central dogma*

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

20 amino acids

but there are only 4 nucleotide bases in DNA

triplet code

a series of nonoverlapping, three nucleotide sequences

forms a polypeptide

these sequences are then translated into a chain of amino acids

sequence of mRNA

sequences if gene are transcribed into complementary non overlapping three nucleotide

during transcription

one of the two DNA strands called template strand provides a template for ordering the sequence of complementary nucleotides in an RNA transcript

template strand

one of the two DNA strands

always the same

the template strand is ____ for any given strand

codons

mRNA base triplets/ read in the 5 to 3 direction

amino acid

each codon specifies the ____ to be placed at the corresponding position along a polypeptide

64

codons were deciphered by the mid-1960s

61 codons

code for amino acids

3

triplets are “stop” signals to end translation

redundant

more than one codon may specify a particular amino acid

ambiguous

no codon specifies more than one amino acid

reading frame

codons must be read in the correct ____ in order for specified polypeptide to be produced

non overlapping fashion

codons are read one at a time

universal

the genetic code is ___/shared by the simplest bacteria and the most complex animals

RNA synthesis

is catalyzed by RNA polymerase, which pries the DNA strNDS APART AND JOINS TOGETHER THE RNA NUCLEOTIDES

RNA polymerase

assemble polynucleotides in the 5-3 direction

unlike DNA polymerase

RNA polymerase can start a chain without a primer

promoter

the DNA sequence where RNA polymerase attaches to to ______ in bacteria the sequence singing the end of transcription is called the terminator

transcription

initiation, elongation, termination

promoters

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

TATA box

crucial in forming the initiation complex in eukaryotes

transcription factors

meditate the binding of RNA polymerase and the initiation of transcription

RNA polymerase II

bound to a promoter is called a transcription initiation complex

As RNA polymerase moves

along the DNA it untwists the double helix, 10 to 20 bases at a time

40 nucleotides per second

transcription progresses at a rate of

Mechanisms of termination

Are different in bacteria and eukaryotes

In bacteria

The polymerase stops transcription at the end of the terminator and the mRNA can be translated without further modification

In eukaryotes

RNA polymerase II transcribes the polyadenylation signal sequence

The RNA transript

Is released 10-35 nucleotides past the polyadenylation

Enzymes in the eukaryotic nucleus modify

Pre-mRNA before the genetic messages are dispatched to the cytoplasm

Ends of the primary transcript are altered

Some interior parts

Of he molecule are cut out and the other parts spliced together

5’ end

Receives a modifies G nucleotide 5’ cap

3’

End gets a poly-A tail(eukaryotes)

Eukaryotic mRNA

Have long non coding stretches of nucleotides that lie between coding regions

Intervening sequences or intron*

The noncoding regions

Exon

The other regions and are usually translated into amino acid sequences

RNA splicing

Removes introns and joins exons, creating an mRNA molecule with continuous coding sequence

Alternative RNA splicing

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

Spliceosomes *

Consist of proteins and small RNA

Ribozyomes

Are RNA molecules that function as enzymes

Transfer RNA (tRNA)

A cell translates an mRNA message into protein with the help of -____

tRNAs

Transfer amino acids to the growing polypeptide in a ribosome

Each tRNA

Can translate a particular mRNA codon into a given amino acid

Nucleotide triplet

The tRNA contains an amino acid at one end and at the other end has a ______ that can pair with eh complementary codon on RNA

80 nucleotides long

A tRNA molecule consists of a single RNA strand

Cloverleaf

Flattened into one plane, a tRNA molecule

First

A correct match between a tRNA and an amino acid,done by the enzyme aminoacyl-tRNA *synthetase

Second

A correct Mach between the tRNA anticodon and an mRNA codon

Wobble

Flexible pairing at the third base of a codon and allows some tRNAs to bind to more than one codon

Ribosomes

Facilitates specific coupling of tRNA anticodons with mRNA codons during protein synthesis

Proteins and ribosomal RNA

He large and small ribosomal subunits

A site

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

P site

Holds the tRNA that carries the growing polypeptide chain

E site

The exit site where discharged tRNAs leave the ribosome

Three stages of translation

Initiation, elongation, termination

Protein “factors”

Initiation, elongation and termination require,, aid in the translation process

Initiation stage of translation

Brings together mRNA and tRNA with the first amino acid and the two ribosomal subunits

Start codon

The small subunit moves along the mRNA until it reaches AUG

elongation

amino acids are added one by one to the previous amino acid at the c-terminus 0f the growing chain

elongation factors

codon, recognition, peptide bond formation, and translation

translation

proceeds along the mRNA in a 5’ to 3’ direction

termination

occurs when a stop codon in the mRNA reaches the A site of the ribosome

release factor

the A site accepts a protein

the release factor

causes the addition of the water molecule instead of an amino acid

polypeptide

the release factor releases ____ and the translation assembly then comes apart

free ribosome and bound ribosome

two populations of ribosomes are evident in cells

free ribosomes

mostly synthesize proteins that function in the cytosol

place simultaneously

in bacteria the transcription and translation can take

nuclear envelope

separates transcription and translation

mutations

are changes in the genetic material of a cell or virus

point mutation

chemical changes in just one or a few nucleotide pairs of a gene//within a gene can be divided into two general categories

nucleotides

pair substitutionsi

insertion/deletion

one or more nucleotide pair

subsitiution

a nucleotide pair _____ replaces one nucleotide and its partner with another pair of nucleotidesm

silent mutations

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

missense

mutations still code for an amino acid but not correct amino acid

substitution

mutations are usually missense mutations