UNIT 1 INFORMATION METHODS OF A CELL

What do you know about DNA?• Building blocks are called?

– nucleotides

• The shape is ?– Double helix

• The three primary components of a nucleotide are?– Sugar, phosphate, nitrogen base

• Where are each of these found?– The sugar and phosphate are in the backbone; the nitrogen base is on the rungs between DNA strands

• The sugar is?– deoxyribose

DNA RNA

DNA Backbone Structure• Alternate phosphate and sugar (deoxyribose), phosphate ester bonds

DNA Backbone Structure• Alternate phosphate and sugar (deoxyribose), phosphate ester bonds

DNA RNA

DNA RNA

DNA Primary Structure Summary• Backbone (sugar+phophate with phosphate ester bonds and base side chains)

DNA RNA

What are the base pairing rules for DNA?

DNA Double Helix• Base pairing by unique hydrogen bonds

• C - G and A - T pairs

DNA Double Helix• Base pairing by unique hydrogen bonds

• C - G and A - T pairs

• Each strand of the double helix is oriented in the opposite direction

• What is this arrangement called?

• “Antiparallel “

Figure 10.5B

5 end 3 end

3 end 5 end

P

P

P

PP

P

P

P

What process is used in the cell to make

new strands of DNA?

DNA Replication

DNA

What do you remember?

• What does semi conservative replication mean?

– The resulting DNA includes one original strand and one new strand

– One original strand is “conserved” or saved.

Untwisting and replication of DNA

• each strand is a template for a new strand

Figure 10.4B

helicase

DNA polymerase

What is the job of the helicase enzyme?– To unzip the DNA

What is the job of the DNA polymerases?

– To build new DNA strands by attaching nucleotides to the parent strand

What is the job of ligase?– To attach fragments of DNA together

DNA Replication• Complementary base pairs form new strands.

• DNA polymerase works in only one direction

5 end

P

P

Parental DNA

Figure 10.5C

DNA polymerasemolecule

53

35

35

Daughter strandsynthesizedcontinuously

Daughter strandsynthesizedin pieces

DNA ligase

Overall direction of replication

53

• Telomere sequences are lost with each replication.

• Cancer, aging

telomeres

So what is a telomere anyway?

• A telomere is a repeating DNA sequence (for example, TTAGGG) at the end of the body's chromosomes.

• The telomere can reach a length of 15,000 base pairs. • Telomeres function by preventing chromosomes from losing base pair sequences at their ends. They also stop chromosomes from fusing to each other.

• Each time a cell divides, some of the telomere is lost (usually 25-200 base pairs per division).

• When the telomere becomes too short, the chromosome reaches a "critical length" and can no longer replicate.

• This means that a cell becomes "old" and dies by a process called apoptosis.

So what do telomeres have to do with

Cancer?• Its all about the enzyme, telomerase.• Telomerase causes the continued addition of DNA ends (telomeres) so cells with active production of telomerase continue to grow and divide. Body cells no longer produce telemerase.

• What kind of cells keep growing and dividing?

• Fetal cells, tumor cells including cancer cells

• DNA replication begins at many specific sites

How can entire chromosomes be replicated during S phase of the cell cycle?

Figure 10.5A

Parental strandOrigin of replication

Bubble

Two daughter DNA molecules

Daughter strand

What are these sites called?Replication Bubbles

DNA

DNA

• In transcription, DNA helix unzips

– RNA nucleotides line up along one strand of DNA, following the base-pairing rules

– single-stranded messenger RNA peels away and DNA strands rejoin

– What are the 3 steps of transcription?

RNA polymerase

DNA of gene

PromoterDNA Terminator

DNAInitiation

Elongation

Termination

Area shownin Figure 10.9A

GrowingRNA

RNApolymerase

Completed RNA

Figure 10.9B

DNA

RNA Transcription• In nucleus, DNA guides the synthesis of mRNA

RNA Transcription• RNA polymerase and elongation reaction

RNA Transcription• RNA polymerase and elongation reaction

Eukaryotic RNA is processed before leaving the nucleus

• Noncoding segments, introns, are spliced out

• A cap and a tail are added to the ends

Figure 10.10

DNA

RNAtranscriptwith capand tail

mRNA

Exon Intron IntronExon Exon

TranscriptionAddition of cap and tail

Introns removed

Exons spliced together

Coding sequence

NUCLEUS

CYTOPLASM

Tail

Cap

RNA vs. DNA

• RNA contains Uracil, not Thymine

• Sugar is Ribose• Usually single stranded

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

Sugar(ribose)

Phosphategroup

Types of RNA• mRNA contains codons which code for amino acids.

DNA

Types of RNA• rRNA - Ribosome - contains enzymes and keeps everything together

Types of RNA• tRNA - Transfer RNA carries amino acid and read codons on m-RNA through its

own anticodons.

Types of RNA• tRNA - Transfer RNA carries amino acid and read codons on m-RNA through its

own anticodons.

Protein Synthesis

Protein Synthesis

Protein Synthesis

Protein Synthesis

Protein Synthesis

Check

• The following section of DNA is used to build a strand of mRNA

• 3’ – GAA- CCC- TTT- 5’• What is the corresponding mRNA sequesnce?

• What are the anticodons on the tRNA in the next step?Modified from www.elmhurst.edu/~chm/onlcourse/CHM103/Rx22DNA.ppt

• Summary of transcription and translation

Figure 10.15

1Stage mRNA istranscribed from aDNA template.

Anticodon

DNA

mRNARNApolymerase

TRANSLATION

Enzyme

Amino acid

tRNA

InitiatortRNA

Largeribosomalsubunit

Smallribosomalsubunit

mRNA

Start Codon

2Stage Each amino acid attaches to its proper tRNA with the help of a specific enzyme and ATP.

3Stage Initiation of polypeptide synthesis

The mRNA, the first tRNA, and the ribosomal subunits come together.

TRANSCRIPTION

Figure 10.15 (continued)

4Stage ElongationGrowingpolypeptide

Codons

5Stage Termination

mRNA

Newpeptidebondforming

Stop Codon

The ribosome recognizes a stop codon. The poly-peptide is terminated and released.

A succession of tRNAs add their amino acids to the polypeptide chain as the mRNA is moved through the ribosome, one codon at a time.

Polypeptide