Biology Chapter 4 & 5

DNA is made of these three components

a deoxyribose sugar

a phosphate group

a nitrogenous base

what bond attaches the nitrogenous base to the 1' carbon

glycosyl bond

what bond attaches the phase group to the 5' carbon

ester bond - phosphodiester bond

A-T has how many h-bonds

2

G-C has how many h-bonds

3

purines (two chemical rings)

adenine and guanine

pyrimidines (one chemical ring)

cytosine, uracil, and thymine

dna replication is...

semiconservative: each one of the parent strand makes a newly synthesized strand

areas where the replication fork are close to other ones are called a

replication bubble

replication fork

area of DNA that's just about to be seperated

helicase

unwinds double helix by breaking h-bonds

SSBs

bind to single strand to prevent them from recombining

DNA gyrase

introductes negative supercoiling to help DNA unwind

RNA primer

starting point for DNA polymerase III by making short RNA strand later replace d with dNTPs

DNA polymerase III

NEEDS RNA PRIMER - builds in the 5' to 3' direction

leading strand: builds in one continuous strand

lagging strand: bilds in small fragments (okazaki fragments)

leading strand

5' to 3'

lagging strand

3' to 5'

ligase

connects okazaki fragments on laagging strand into one via phsphodiester bond

DNA polymerase I

removes primers, replaces them with dNTPs

dNTPs

used to make DNA, same as nucleotides but has 3 phosphate groups. 2 of the phosphates are used by DNA polymerase III for energy

2 steps in protein synthesis:

transcription and translation

3 differences of RNA from DNA

RNA is single stranded (DNA is double stranded)

RNA has uracil (DNA has thymine)

RNA has a hydroxyl group on 2' carbon (DNA only has a hydrogen on 2')

3 phases of transcription

initiation, elongation, terminatio

what happens in initiation of transcription?

RNA polymerase binds to a specific site of DNA usually dense with A=T. A promotor (start point) indiciaes for RNA polymerase to begin

what happens in elongation of transcription?

mRNA is build in the 5' to 3' direction. the DNA used for code for mRNA is the TEMPLATE STRAND

template strand

DNA strand used to code for mRNA

coding strand

DNA strand not used to code for mRNA

what happens in termination of transcription?

at the of the gene, a terminator sequence tells RNA polymerase to stop

if the template strand is ATTG, what is the coding strand? what is the mRNA?

coding strand: TAAC

mRNA: UAAC

what is added to the start and end of RNA in eukaryotic cells?

a 5' cap at the start, and 200 adenine base pairs (poly-A tail) at the 3' end

what enzyme puts 200 adenine base pairs on the 3' end of mRNA

poly-A polymerase

what does capping and tailing do?

protects mRNA from digestion in cytoplasm, helps iniate translation

exons

coding regions

introns

non-coding regions

what cuts introns off mRNA?

spliceosomes

genes are turned on when required by ...

transcription factors

housekeeping genes

genes that must be on all the time and must be transcribed and translated constantly

4 levels of gene regulation (eukaryotic cells)

1. transcriptional

2. post-transcriptional

3. translational

4. post-translational

transcriptional gene regulation

regulates which genes are transcribed or controls the rate

post-transcriptional gene regulation

mRNA undergoes changes in the nucleus before translation. removal of introns and splicing of exons together

translational gene regulation

controls the time translation takes, or the time it takes for used mRNA to break down in the cytoplasm

post-translational gene regulation

the rate at how long it takes for a protein to become active and how long it can remain functioning, as well as adding various chemical groups to it

histone

an 8-member protein that every 200 nucleotides coil around

DNA/RNA polymerase builds in the ... and reads in the ...

builds in the 5' to 3'

reads in the 3' to 5'

oncogenes

damaged copies fo genes that control normal cell growth and division

mutations

mistakes in DNA that are inherited

types of mutations

1. silent mutation

2. missense mutation

3. nonsense mutation

4. frameshift mutation

silent mutation

no effect on cell's operation and usually occur in the non-coding region of DNA, very common. may be cut out when mRNA is prepared to be sent out for translation. does not change the amino acid

missense mutation

codon is altered resulting in different amino acid in potein sequence

nonsense mutation

when a change in DNA sequence causes a stop codon to occur too early. harmful because a large part of protein might not be made

frameshit mutation

addition or loss of DNA that changes the reeading frame for gene

types mutations in large segements of DNA

1. deletion

2. duplication

3. inversion

4. reciprocal translocation

spontaneous mutation

error in genetic machinery

point mutation

when DNA is checked for errors and a base pair is missed

induced mutation

caused by exposure to mutagenic acids like carcinogens (X rarys, radiation, chemicals)

aminoacyl-tRNA

when tRNA has the amino acid attached

what 3 sites are used for tRNA building

1. A (acceptor) site

2. P (peptide) site

3. E (exit) site

how does elongation of the polypeptide chain occur?

the tRNA first takes the (AUG) amino acid methionine to the P site, the next tRNA carries the following apporpriate amino acid to the A site.

the two amino acids attach together at the P site as it attaches to the growing peptide, forming a peptide bond

what happens after the first peptide bond forms in translation?

the ribosomes shift over one codon at a time. A site to P site where peptie grows.

The P site tRNA moves to the exit sie as it leaves without an amino acid. they return to pick p more of the apporpriate amino acid

how does translation stop?

termination occurs when ribosome encounters a 'stop' codon. A protein called the RELEASE FACTOR is activated and seperates the two subunits

What is the function of nuclease in DNA repair?

Nucleases are enzymes that cut out damaged sections of DNA so they can be replaced with correct nucleotides during DNA repair.

What is the purpose of DNA replication?

To copy DNA before cell division.

Where does DNA replication occur in eukaryotic cells?

In the nucleus.

What enzyme unwinds the DNA double helix?

Helicase.

What do single-strand binding proteins (SSBs) do?

Prevent DNA strands from reannealing.

What enzyme adds nucleotides during DNA replication?

DNA Polymerase III.

What enzyme adds the RNA primer?

Primase.

What enzyme removes RNA primers and replaces them with DNA?

DNA Polymerase I.

What enzyme joins Okazaki fragments?

DNA Ligase.