ap bio unit 6

watson and crick

Developed the double helix model of DNA.

dna is copied during

DNA replication

dna monomers

nucleotides

nucleotides have 3 parts

sugar, phosphate, nitrogen base

four nitrogenous bases

Adenine, Thymine, Guanine, Cytosine

purines (2 rings)

Adenine and Guanine

pyramidines (1 ring)

thymine and cytosine

One strand of a DNA molecule goes from 5' to 3' and the other strand is opposite. this is called

antiparallel

the sides of the dna ladder and made up of sugar and phosphates bonded

covalently

steps of the ladder and made of nitrogen bases held together by

hydrogen bonds

replication begins at sites called

origins of replication, where the two DNA strands are separated, opening up a replication "bubble"

replications proceeds in

both directions from each origin until the entire molecule is copied

At the end of each replication bubble is a

replication fork, a Y-shaped region where new DNA strands are elongating

helicases

enzymes that untwist the double helix at the replication forks

single strand binding proteins

bind to and stabilize single-stranded DNA

Topoisomerase

relieves the strain of twisting of the double helix by breaking, swiveling, and rejoining DNA strands

DNA polyermase requires a

primer to which they can add nucleotides

this initial nucleotide strand is a short RNA primer synthesized by the enzyme

primase

this enzyme starts an rna chain from scratch and adds rna nucleotides one at a time using

the parental dna as a template

the 3' end of the rna primer serves as the

starting point for the new strand

enzymes called dna polymerase catalyze

the synthesis of new dna at a replication fork

each monomer joints the dna strand via a

dehydration reaction

dna polymerases add nucleotides only to the free 3' end of a growing strand - it only elongates in the

5' to 3' direction

Along one template strand of DNA, the DNA polymerase synthesizes a _____________ continuously, moving toward the replication fork.

leading strand

To Elongate the other New Strand, Called the ______________, DNA Polymerase must work in the direction away from the replication fork

lagging strand

the lagging strand is synthesized as a series of segments called ______ which are joined together by ________.

Okazaki fragments; DNA ligase

the proteins that participate in DNA replication form a large complex, a

DNA replication machine

ligase

Joins Okazaki fragments on the lagging strand. joins 3' end of dna thay replaces primer to rest of the leading strand dna

dna polymerase progrades newly made DNA

replacing any incorrect nucleotides

in nucleotide excision repair

a nuclease cuts out and replaces damaged stretches of DNA

dna polymerase can only add nucleotides to the free ______ of RNA primers

3' end

in eukaryotic cells, dna is precisely combined with protiens in a complex called

chromatin

proteins called _____ are responsible for the first level of packing in chromatin

histones

the basic unit of DNA packaging

nucleosome

chromatin is loosely packed during ____ and condensed prior to _______

interphase, mitosis

Loosely packed chromatin is called

euchromatin

during interphase a few regions of chromatin are highly condensed into

heterochromatin

dense packing of the heterochromatin makes it difficult for the cell to

express genetic information coded in these regions

central dogma

DNA -> RNA -> Protein

gene expression includes 2 stages

transcription and translation

Transcription

synthesis of an RNA molecule from a DNA template (produces mRNA)

Translation

the synthesis of a polypeptide using the information in the mRNA

site of translation

ribosomes

in prokaryotes, the translation of mRNA can begin before

transcription has finished

i'm a eukaryotic cell, the nuclear envelope separates

transcription from translation

primary transcript (pre-mRNA)

the initial RNA transcript from any gene prior to processing

in eukaryotes, pre-mRNA is processed and modified

before it leaves the nucleus

the flow of information from gene to protein is based on a

triplet code

triplet code

a series of nonoverlapping, three-nucleotide words

these "words" are then translated into

a chain of amino acids, forming a polypeptidw

template strand is always the same strand used for

transcription in a given gene

during translation the mRNa base triplets called codons are read in the

5' to 3' direction

the nontemplate strand is called the ______ because the nucleotides of this strand are identical to the codons other than T/U

coding strand

Codons must be read in the correct _______ in order for the specified polypeptide to be produced

reading frame

RNA synthesis is catalyzed by

RNA polymerase, which pries the DNA strands apart and joins together the RNA nucleotides

RNA is complementary to the

DNA template strand

RNA polyermase also elongates in a _____ but does not need _____

5' to 3' direction, primer

The DNA sequence where RNA polymerase attaches is called

promoter

the sequence signaling of transcription is called

the terminator

The stretch of DNA that is transcribed is called

transcription unit

3 stages of transcription

initiation, elongation, termination

promoters signal the transcription

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

transcription factors mediate the binding of rna polyermase and the

initiation of transcription

in eukaryotes a promoter called _____ is crucial in forming the invitation complex

TATA box

As RNA polymerase moves along the DNA it untwists the

double helix

A gene can be transcribed simultaneously by several

RNA polymerases

nucleotides are added to the ____ of the growing RNA molecule, elongating yhe rna in the _____ direction.

3' end, 5' to 3'

in bacteria, polyermase stops transcription at the end of the terminator and mRNA can be

translated without further modification

Eukaryotes RNA polymerase || transcribes the

polyadenylation signal sequence

rna processing is in

eukaryotes

Enzymes in the eukaryotic nucleus modify ______ before the genetic messages are dispatched to the cytoplasm

pre-mRNA (RNA processing)

during RNA processing

both ends of the primary transcript are usually altered

the 5' end receives a ____ and the 3' end gets a ____.

5' cap, poly-A tail

non coding regions are called

intervening sequences or introns

other regions are called

exons 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

spliceosomes

consist of a variety of proteins and several small nuclear ribonucleoproteins (snRNPs) that recognize the splice sites

ribozymes

catalytic RNA molecules that function as enzymes and can splice RNA

3 properties of RNA that enable it to function as an enzyme

1. It can form a three-dimensional structure because of its ability to base-pair with itself

2. Some bases in RNA contain functional groups that may participate in catalysis

3. RNA may hydrogen-bond with other nucleic acid molecules

Some introns contain sequences that may

regulate gene expression

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

alternative RNA splicing

as such, the number of different proteins an organism can produce is much greater than its number of

genes

proteins often consist of discrete regions called

domains

Different exons code for different ________ in a protein

domains

exon shuffling may result in

the evolution of new proteins (exons code the domain)

a cell translates mRNA into protiens with the help of

transfer RNA

tRNAs transfer amino acids to the

growing polypeptide in a ribosome

each tRNA molecule enables translation of a given

mRNA codon into a certain amino acid

each has a _____ on w end and and an _____ in the other end.

amino acid, anticodon

the anticodon base pairs with a

complementary codon on mRNA

a tRNA molecule consists of a

single RNA strand (has hydrogen bonds)

Accurate translation requires two steps

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

Second: a correct match between the tRNA anticodon and an mRNA codon

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

wobble

ribosomes

facilitate specific coupling of tRNA anticodons with mRNA codons in protein sybthesis

The two ribosomal subunits (large and small) are made of

proteins and ribosomal RNA (rRNA)

Ribosomes has three binding sites for tRNA

P site, A site, E site

the P site

holds the tRNA carrying the growing polypeptide chain

the A site

holds the tRNA carrying the next amino acid to be added to the chain

the E site

the exit site, where discharged tRNAs leave the ribosome

3 stages of translation

initiation, elongation, termination