what is the function of dna?. making proteins when genes are expressed, proteins are synthesized it...

What is the function of DNA?

• Making proteins• When genes are expressed, proteins are

synthesized

• It involves two stages – transcription and translation

Learning Outcomes

• Explain the processes involved in transcription

• The different nucleic acid needed and its structure

• Explain the difference between primary and mature transcript

DNA recap .... answer these ...

1. An examples of? MY LOPER

2. Made up of?

3. Different types of bases?

4. Number of strands?

5. Held by?

6. What is the triplicate code?

DNA is a nucleic acid, made of long chains of nucleotides

DNA and RNA are polymers of nucleotides

Nucleotide

Phosphate group

Nitrogenous base

Sugar

Polynucleotide Sugar-phosphate backbone

DNA nucleotide

Phosphategroup

Nitrogenous base(A, G, C, or T)

Thymine (T)

Sugar(deoxyribose)

• DNA has four kinds of bases, A, T, C, and G

Figure 10.2B

Pyrimidines

Thymine (T) Cytosine (C)

Purines

Adenine (A) Guanine (G)

DNA recap .... answer these ...

1. An examples of? Polymer

2. Made up of? Nucleotides (deoxyribose, phosphate and base)

3. Different types of bases? Arginine, Thymine, cytosine, guanine

4. Number of strands? 2

5. Held by? Weak hydrogen bonds between strands, covalent bonds between nucleotides (deoxyribose 3’ and 5’)

6. Triplicate code? 3 bases code for an amino acid

RNA• RNA is ribonucleic acid.

• It provides a bridge between DNA and protein synthesis.

• Like DNA, RNA is also made up of nucleotides. What is a nucleotide?

• However the nucleotides in RNA are slightly different! Spot the differences .....

• RNA is also a nucleic acid

– different sugar (ribose – still pentose)

– U (uracil) instead of T

– Single strand, usually

Phosphategroup

Nitrogenous base(A, G, C, or U)

Uracil (U)

Sugar(ribose)

RNAThe three types of RNA are:

– messenger RNA (mRNA)– ribosomal RNA (rRNA)– transfer RNA (tRNA)

mRNA is:– Formed from the DNA in the nucleus.– Small enough to fit through the pores

in the nuclear membrane.

mRNA comtinued ..

– Found in the nucleus and cytoplasm.– A “bridge” molecule between DNA and

protein.– Made by a process called transcription.– Made of thousands of bases in 3s called

codons– Transcribe the mRNA, and split into

codons.

mRNA comtinued ..

– Found in the nucleus and cytoplasm.– A “bridge” molecule between DNA and

protein.– Made by a process called transcription.– Made of thousands of bases in 3s called

codons

U G U A C U G U G C U G

rRNA– Make up ribosomes with proteins. – Made in nucleolus of nucleus and passed

out into cytoplasm via the nuclear pores. – Remain as free ribosomes or attached to

endoplasmic reticulum.

tRNA – Found only in the cytoplasm.– Only 3 bases exposed in 3D structure– General structure of “cloverleaf”– Made of two ends-

• 1 is the anti-codon which binds to a specific mRNA codon.

• 1 is the amino acid binding site.

tRNA

– Specific to an amino acid.– Degenerative code (as

more than one codon for an amino acid)

Amino acids – all similar structure with an amino group and a carboxyl acid group, “R” group changes

Genetic Code2nd base1st base

U C A G3rd base

UUU Phe UCU Ser UAU Tyr UGU Cys U

UUC Phe UCC Ser UAC Tyr UGC Cys C

UUA Leu UCA Ser UAA Stop UGA Stop A

U

UUG Leu UCG Ser UAG Stop UGG Trp G

CUU Leu CCU Pro CAU His CGU Arg U

CUC Leu CCC Pro CAC His CGC Arg C

CUA Leu CCA Pro CAA Gln CGA Arg A

C

CUG Leu CCG Pro CAG Gln CGG Arg G

AUU Ile ACU Thr AAU Asn AGU Ser U

AUC Ile ACC Thr AAC Asn AGC Ser C

AUA Ile ACA Thr AAA Lys AGA Arg A

A

AUG Met* ACG Thr AAG Lys AGG Arg G

GUU Val GCU Ala GAU Asp GGU Gly U

GUC Val GCC Ala GAC Asp GGC Gly C

GUA Val GCA Ala GAA Glu GGA Gly A

G

GUG Val GCG Ala GAG Glu GGG Gly G*Met and initiation.

RNA SUMMARY

• 3 types; mRNA (messenger), rRNA (ribosomal) and tRNA (transfer)

• mRNA; carries a copy of the DNA code from the nucleus to the ribosome in the cytoplasm

• rRNA; formed at the ribosome alongside protein

• tRNA; carries an amino acid to the ribosome in the cytoplasm

DNA molecule

Gene 1

Gene 2

Gene 3

DNA strand

TRANSCRIPTION

RNA

Polypeptide

TRANSLATIONCodon

Amino acidPro

cess

to p

rote

in ..

..

Transcription

• Watch these videos and place the statements in order ....

Higher education Scotland

Crash course 2.21-7.04.

DNALC

McGraw Hill

Transcription produces genetic messages in the form of mRNA

3’

RNApolymerase

RNA nucleotide

Direction oftranscription

Newly made RNA

Templatestrand of DNA

3’

5’

5’

DNA vs RNA

• Compare the 2 nucleic acid types.

RNA vs. DNA

• RNA contains the sugar ribose; DNA contains deoxyribose.

• RNA contains the base uracil; DNA contains thymine instead.

• RNA is usually single stranded; DNA is usually double stranded.

• RNA is short: one gene long at most; DNA is long, containing many genes.

RNA vs. DNA

RNA

1. Complete the following table to compare RNA and DNA

RNA DNANumber of strands

Found in…..

Sugar present

Organic bases

Number of types

Length of strand

13

G, C, A & TG, C, A & URACIL

deoxyriboseribose

Nucleus onlyNucleus & cytoplasm

21

Short Long

Transcription Test1. How many bases in the genetic code

correspond with an amino acid?

2. Draw the section of the mRNA strand that would be transcribed from section X on the DNA shown.

3. Which enzyme would direct this process?

4. What is the difference between an intron and an exon?

5. What happens to primary transcript of mRNA?

6. What is the name of this process?

A T G G G C A T A CT A C C C G T A T G

Transcription Test

1. 3, triplicate code

2. Top one, 3’ to 5’

3. RNA polymerase

4. Exon is expressed as it is the coding region, intron is non-coding region – polypeptide is fragmented

5. From primary transcript Introns are removed and exons are spliced together to form mature mRNA

6. RNA splicing

U A C C C G U A U G

Remember RNA? or ID badges

1. How many types?

2. Location?

3. What are each of their structures (and label within) and functions?

4. Any specific names gives? Lengths?

Remembering RNA ...

http://www.mfpl.ac.at/rna-biology/rna-history/

RNAmRNA tRNA rRNA

Location Nucleus and cytoplasm

Cytoplasm Ribosome

Lengths Longer 3 bases exposed N/A

Structure Codon (from DNA template), made up of introns/exons (exons spliced for mature mRNA

Cloverleaf, 1 leaf Anticodon (against mRNA), stalk is amino acid

Part of ribosome with protein

Learning Outcomes

• Review the process of transcription• Describe the process of translation

DNA molecule

Gene 1

Gene 2

Gene 3

DNA strand

TRANSCRIPTION

RNA

Polypeptide

TRANSLATIONCodon

Amino acid

TranslationOccurs in cytoplasm (mature mRNA transcript

through nuclear pore) on the ribosome

(enzymes needed for protein synthesis).

• Site E; releases (discharges) tRNA after amino acid (aa) part of polypeptide

• Site P – next tRNA held by H bond to mRNA

• Site A – holds next tRNA with its aa then peptide linked to previous aa (P)

5’ 3’

Translation .....

Translation

• Occurs in cytoplasm (mature mRNA transcript through nuclear pore) on the ribosome.

1. A ribosome attaches to the mRNA at an initiation codon (AUG). The ribosome encloses two codons.

3.The next amino acid-tRNA attaches to the adjacent mRNA codon (leu in this case) - The codon and anticodon bases

matching up

Translation

2. met-tRNA diffuses to the ribosome and attaches to the mRNA initiation codon by complementary base pairing

4. The bond between the amino acid and the tRNA is cut and a peptide bond is formed between the two amino acids.

5 The ribosome moves along one codon so that a new amino acid-tRNA can attach. The free tRNA molecule leaves to collect another amino acid. The cycle repeats from step

6. The polypeptide chain elongates one amino acid at a time, and peels away from the ribosome, folding up into a protein as it goes. This continues for hundreds of amino acids until a stop codon is reached, when the ribosome falls apart, releasing

the finished protein.

Steps in translation SUMMARY

1. Initiation – needs start codon (AUG, for methionine) in P site with anti codon?

2. Elongation – complementary tRNA bring correct amino acids which are added through a peptide bond

3. TerminationA stop codon (AUU, AUC or UGA) which has a release factor which frees the polypeptide from ribosome.

Translation

• Multiple translation can occur with many ribosomes reading the same mRNA – the ribosomes on the same mRNA are called - polysomes or polyribosome

• Translation requires ATP!

What’s happening?

Now explain the WHOLE process

Animate/Model/Demonstrate

• Can you animate it? • Anyway possible – here is my original ......