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LECTURE 5:

DNA, RNA & PROTEINS

DNA structure and replication

RNA

Structure

Transcription

Translation

Protein synthesis

Amino acids

Mutations

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DNA Deoxy_______________ Acid (DNA)

is the blueprint for life:

contains ALL the necessary information to

make a new organism

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DNA structure DNA is a polymer of

nucleotides

Each nucleotide composed of

a p________________,

a s__________ (deoxyribose),

and organic

nitrogenous base.

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Four DNA bases

Four kinds of_______________ bases:

P_________ bases

A = AdenineG = Guanine

Pyrimidine basesT = Thymine

C = Cytosine

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The four nucleotides of DNA

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DNA: Complimentary base p______

Adenine pairs with __________

A T

Cytosine pairs with _________

C GEach DNA strand is a compliment

of the other

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DNA STRUCTURE

DNA is a _________ helix

Discovered by

Watson and Crick, 1953

The backbone of DNA:formed by sugar-phosphate

chemical bonds

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DNA structure: Double _______

DNA is like a ladder:

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DNA REPLICATION

(in the nucleus)

Each DNA strand

becomes a _______________,

parent strand becomes apart

Proper base-pairs are

assembled on that template

(with proper enzymes:

polymerase and ligase).

Theres always a pool of

nucleotides (A,C,T,G) in the nucleus

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DNA replication Nucleotides are connected together to make

a new strand that is c_______________ tothe old strand.

The new double strand is

________ to the old double strand

S_____-conservative replication:

half old, half new DNA

on each strand

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A-T vs. G-C bond

A-T is a __________ bond

C-G is a ________ bond (stronger)

DNA double strand can separate into 2 single

strands when heated.

Which strand would require more heat (moreenergy) to separate: an A-T rich or a C-G rich

double strand?

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RNA structure and synthesis

RNA: R______________ Acid

Is very similar to DNA

(repeating subunits, nucleotides).

Difference between RNA and DNA:

Each nucleotide contains a different _______:

ribose instead of deoxyribose.Bases are A, G, C, and U (uracyl, not thymine)

A pairs with U; G pairs with C

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RNA

RNA is ___________ stranded

and shorter

RNA is __________ stable than DNA:

RNA doesnt persist in the cell for long

(sometimes it exists for a few seconds),

whereas DNA can persist for the life of the

cell.

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Differences between DNA and RNA

__________

__________

__________

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CENTRAL DOGMA

DNA

________

Proteins

3 different RNA molecules involved in protein

synthesis: M______________ RNA (mRNA)

R______________ RNA (rRNA)

T______________ RNA (tRNA)

transcription

translation

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Transcription: DNA RNA

TRANSCRIPTION: RNAsynthesis from DNA.

T___________: makingan RNA copy, called

m______________ RNA

(mRNA), of a small partof the DNA molecule.

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Transcription: DNA RNA

Transcription occurs in the N_____________ mRNA carries the message about what type of

protein to make from the DNA in the nucleus tothe ribosome

The nucleotide sequences of RNA and DNA arethe same (except in RNA uracil is used instead ofthymine)

mRNA is synthesized from DNA using basepairing

DNA unwinds in a section

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T______________ of RNA from a

template strand of DNA

RNA polymerase attaches at the promoter sequence of DNA,and it moves along the DNA, unzipping the strandsthis

allows for one mRNA molecule to be formed.

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During _____________, a molecule ofmessenger RNA is formed as a complementary

copy of a region on one strand of the DNA

molecule

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Transcription

Once mRNA is formed, enzymes in the nucleus

remove the i__________ (non-coding regions)

and leave the exons (expressed segments)

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The Genetic Code Each 3 consecutive bases on the mRNA is a code

word, codon, that specifies an amino acid.

The genetic code consists of ______ codons,(4x4x4), but only 61 code amino acids.

Three codons act assignal terminators

(UAA, UAG, UGA)

One codon, AUG, codes formethionine, and is also the

_________ signal for translation.

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The Genetic Code The G__________ Codeevery ______ nucleotides on

mRNA codes for a particular amino acid (3 at a time) Code is universaltrue for all organisms!

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20 Amino Acids

There are _____ aminoacidsthey are like

the bricks, or

building blocksto make

all proteins

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Translation: RNA Protein

T_______________: synthesizing a protein fromamino acids, according to the sequences of the

nucleotides in mRNA.

Occurs at the ___________, in cytoplasm of cell Ribosomal RNA, rRNA, is needed for protein

synthesishelps mRNA bind to ribosome.

Transfer RNA, tRNA, brings specific aminoacids to the ribosome to be assembled as

proteins.

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Translation R______________ RNA, rRNA, joins with a

number of proteins to form ribosomes Ribosomes are the sites of _____________

synthesis

Ribosomes consist ofa large subunit and

a small subunit.

mRNA binds to thesmall subunit.

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T___________ RNA (tRNA)

Transport moleculethat carries specific

amino acids to a

ribosome

(80 nucleotides long)

Folded

Each tRNA recognizes

the correct codon on

the mRNA molecule

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Steps in T_____________

1. mRNA leaves the nucleus and migrates to ribosome

2. mRNA binds to small ribosomal subunit

3. tRNA brings an amino acid to the ribosome, where

anticodon on the tRNA binds to the codon of the

mRNA4. The amino acid bonds to its adjoining amino acid to

form a growing polypeptide molecule

5. The tRNA without the amino acid is released from the

ribosome

6. Other tRNAs bring amino acids to the ribosome to

complete the protein molecule

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Protein synthesis

Occurs in the cytoplasm of the cell A____________ acids are the repeating sub-

units of protein molecules.

Amino acid order determines the protein

20 amino acids exist in all life forms

O____________ of amino acids is important,

determines the 3-dimensional shape of themolecule.

Structure of the protein determines its function

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Proteins Biological activity (function) of proteins depends

largely on its 3-D _______________

S

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Summary:

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Genomic Geography In Cell Nucleus: RNA is produced by transcription.

RNA is single-stranded; substitutes the sugar ribose for

deoxyribose and the base uracil for thymine Messenger RNA or mRNA, conveys the DNA recipe for protein

synthesis to the cell c______________.

mRNA binds to ribosome, each three-base codon of the mRNA

links to a specific form oftransfer RNA (tRNA) containing the complementary three-base

sequence.

This tRNA, in turn, transfers a single _________ acid to a growing

protein chain. Each codon directs the addition of one amino acid to the protein.

Note: the same amino acid can be added by different codons; in

this illustration, the mRNA sequences GCA and GCC are both

specifying the addition of the amino acid alanine (Ala).

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Important

Both DNA and RNA have a direction: one end is

the 3 the other is the 5 end.

Thus, ________ are read in one direction only.

Also, note there is redundancy in the genetic

code: the different sequences can specify for the

same amino acid.

Example: UUA and UUG = Leucine

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When things go wrong Mutations: changes in the DNA sequence, that

may be passed along to future generations. P________ mutations: a single base substitution

THE CAT SAW THE RAT

THE CAT SAW THE HAT

D____________: a small DNA segment is lostTHE CAT SAW THE RAT

THE AT SAW THE RAT

Insertion: a segment of DNA is added

THE CAT SAW THE RAT

THE CHAT SAW THE RAT

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Mutations Frame-________ mutation: modification of the reading

frame after a deletion or insertion, resulting in all codonsdownstream being different.

For example:

THE RAT SAW THE CAT AND RAN

If you take out the R in RAT and shift the frames, youget:

THE ATS AWT HEC ATA NDR AN

The resulting sentence (or mRNA message) ismeaningless!

THE OLD MAN AND THE SEA

THE LDM ANA NDT HES EA

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Somatic Mutations

S____________ mutations: occur in ________cells, or cells that do not lead to gametes.

Somatic mutations that occur in leaves, roots or

stems are usually not passed on to futuregenerations

UNLESS the plant reproduced _____________.