DNA & RNA : BIO 107

Lec 30 - 35

What is DNA made of?

Nucleotides joined together into long strands

Nucleotides within strands

joined by covalent bonds

Nucleotides between strands

joined by H-bonds; forming complementary base pairs

DNA is a

right handed helix, 2 nm wide

left handed helix, 2 nm wide

DNA in Prokaryotes

chromosome is large and circular

plasmid is small and circular

Prokaryote chromosome

genetic material; carry needed genes for growth and reproduction

Prokaryote plasmid

carry optional traits

DNA in Eukaryote

nuclear chromosome is linear and is wrapped around histone proteins → forms nucleosome

organelle chromosome is circular

Eukaryote nuclear chromosome

linear and wrapped around histone proteins

Eukaryote organelle chromosome

is circular

Nucleic acid rules #1

Made using triphosphate nucleotides

Nucleic acid rules #2

Made 5' to 3'

Nucleic acid rules #3

Made using a ssDNA template

Nucleic acid rules #4

Pair antiparallel

Nucleic acid rules #5

Pair with complementary base pairing

RNA synthesis requires

RNA Pol, NTPs, template DNA strand

DNA replication requires

DNA Pol, dNTPs, template DNA strand,
RNA primer

True or False: RNA primer needed because DNA Pols can’t initiate

True

False

DNA replication starts at

ori (origin of replication)

True or False: Does it replicate in both directions

True

False

Proteins that make the leading strand

Primase & DNA Pol III

DNA Pol III purpose

synthesize DNA strands (fast)

DNA Pol I purpose

Removes RNA primers and replaces it with DNA

Proteins that make the lagging strand

Primase, DNA Pol III, DNA Pol I, & DNA Ligase

topoisomerase function

prevents supercoiling

helicase function

separates strands; only on lagging strand

SSB proteins

keep strands separated

primase function

make RNA primers

DNA repair enzymes replace

damaged nucleotides

Replication of circular DNA starts at

single ori

circular DNA is in

Prokaryote

circular DNA: one ori forms

2 replication forks and finishes when they meet each other

Replication of linear DNA starts at

many oris simultaneously

linear DNA is in

Eukaryotes

linear DNA: each ori forms

two replication forks and finishes when they meets another

Central dogma definition

principle that describes flow of genetic information

Correct order of Central Dogma

DNA → RNA → PROTEIN

RNA → DNA → PROTEIN

What is a gene?

a DNA region responsible for the production of an RNA molecule

3 nt in mRNA =

1 codon

1 codon =

1 amino acid

mRNA written 5’ to 3’ because

makes and reads 5’ to 3’

makes 5’ to 3’

reads 5’ to 3’

RNA synthesis is also called

transcription

RNA synthesis is done by

RNA Pols

RNA synthesis step 1

initiation

RNA synthesis: initiation

1. RNA pols attaches to DNA promoter

2. DNA strands are separated

3. Begins of template strand

What direction is the template strand?

3’ to 5’

5’ to 3’

DNA promoter function

is a specific region of DNA sequence

Genetic transfer factor (TF) protein function

help RNA pol find promoter

RNA synthesis step 2

Elongation

RNA synthesis: elongation

1. RNA pol moves along template strand

2. RNA nucleotides are added

What direction does the RNA strand grow?

5’ to 3’

3’ to 5’

RNA synthesis step 3

termination

RNA synthesis: termination

1. grows until it reaches stop codon

2. RNA strand is released

Intrinsic termination

Done by the RNA itself

RNA sequence forms a hairpin loop that pulls away

Factor-dependent termination

RNA sequence recruits a protein

What is the name of the DNA region where the Pol begins?

Promoter

How many template strands are there?

one

two

Are Primases required in RNA synthesis?

No because it can bind directly to promoter

Are Primases required in DNA replication?

Yes because it synthesizes a short RNA primer

Are helicasese required in RNA synthesis?

No because RNA pol can naturally untwist DNA strands

Are helicasese required in DNA synthesis?

Yes because it separates the strands ahead of the replication fork.

What is the name of the DNA region where the Pol finishes?

Terminator

rRNA processing

1. is cut into pieces by enzymes

2. forms proteins

rRNA function

is a key component of ribosomes

tRNA processing

1. specific bases are modified

2. allow it to fold into complex shapes

tRNA function

helps transfer amino acids to the ribosome during protein synthesis.

mRNA processing

1. A 5' cap is added

2. A poly-A tail is added to the 3' end

how do mRNAs have 5' caps

Done by Capping Factor proteins

how do mRNAs have poly(A) tails

done by cleavage Factor which recruits Poly(A) Pol

Why are these modifications done to mRNA?

1. helps export from nucleus

2. helps Ribosomes bind

3. extends lifespan

Introns

are removed from pre-mRNAs

exons

spliced together and remain in mature mRNA

When do splicesomes remove introns?

After mRNA synthesis

before mRNA synthesis

Disadvantages of having introns

1. Genes are larger

2. mRNAs take more time to make

Advantages of having introns

1. make different versions of similar proteins from same gene