topic2 cell

Subject Matter Expert: Azizah Mohd. Asi (OUM)

Faculty of Science and FoundationStudies

Copyright © FSFS Sept 2005 Open University Malaysia

TOPIC 2: THE NUCLEUS, CHROMOSOME AND DNA

Azizah Mohd. AsiSBBI4103 Cell Biology and Cellular BiochemistrySeptember 2005

Subject Matter Expert: Azizah MOhd. Asi (OUM)



•Nucleus

•Chromosome

•DNA structure and function Gene regulation and expression

•DNA replication




NUCLEUS

• What are the importance of nucleus? genetic information carrier DNA replication RNA synthesis

• What are the functions of nucleus?

• What are the structures of nucleus? nuclear envelope chromatin




CHROMOSOME

What is chromosome?• A threadlike structure found in the nucleus.

• Contains both DNA and protein.

• Composed of chromatin or DNA-protein complex.

• Carry the genes in a linear sequence.




CHROMOSOME (2)

Prokaryotic chromosome Eukaryotic chromosome

•Can be found in bacterial cells.

•Can be found in the nucleus of eukaryotic cells – protists, fungi, animals and plants.

•Circular double-stranded DNA molecule packaged into the region called nucleoid. Does not contain chromatin.

•Tightly packaged in the chromosome within the nucleus. Chromatin functions the same to the nucleus as cytoplasm to the entire cell.

•In E.coli DNA molecule contains 4.6 million base pairs.

•In human, the length of the chromosomes vary between 1.6 cm to 8.4 cm (about 1000 times more DNA than E.coli).




CHROMOSOME (3)

The structure of chromosome:• Centromere

• Telomere

• Chromatin

• 30 nm fibre form




CHROMOSOME (4)

The structure of eukaryotic chromosome




CHROMOSOME (4)

The structure of chromatin




DNA STRUCTURE AND FUNCTION

• DNA is made up of four different nucleotides: cytosine adenine thyamine guanine (Which are purines and which are pyrimidines?)

• Each nucleotide is made up of three elements: phosphate deoxyribose sugar nitrogenous base

• A phosphodiester bond links these nucleotides.

(see figures 2.5, 2.6 and 2.7 on pages 22-23)




DNA STRUCTURE AND FUNCTION (2)

DNA structure:

Two complementary anti-parallel chains of DNA wound around each other following a helical path, resulting in a right-handed double helix.





BASE PAIRING:

Purine – Pyrimidine

T – A

C – G





The Central Dogma

DNA RNA PROTEIN TRANSCRIPTION TRANSLATION

(see Figure 2.12 on page 28) DNA codes for the production of RNA RNA codes for the production of protein Protein DOES NOT code for the production

of protein, RNA or DNA(Is there exception for these rules, ie. reverse transcribe?)





•Gene regulation and expression Transcription Translation Eukaryotic gene expression Prokaryotic gene expression




GENE EXPRESSION

Eukaryotic Prokaryotic•Transcription – in the nucleus; translation – in the cytoplasm; mRNA longer-lived

•Transcription and translation – in the cytoplasm

•mRNAs encode only one protein - monocistronic

•mRNA may contain regions coding for one or more proteins, or polycistronic

•Forms pre-mRNAs that would undergo splicing, capping and polyadenylation, to form mature mRNA




GENE EXPRESSION (2)

DO YOU KNOW, WHAT IS:

• a promoter?

• a terminator?

• an intron?

• an exon?

• RNA Pol II?

• snRNP?During eukaryotic gene expression the pre-mRNA would

undergo splicing and capping to form mature mRNA that will be transported to the cytoplasm. Why is this so?




DNA REPLICATION

•What is DNA replication?

•How do DNAs replicate?

• When do DNAs replicate?

•What is a replicon?




SUMMARY• Eukaryotic nucleus carries the genetic information of the cell in multiple chromosomes, each

containing a single DNA molecule.

• Eukaryotic cells have true nucleus (membrane-bounded) while prokaryotic cells have nuclear material (a circular double-stranded DNA molecule) concentrated in a region called nucleoid (does not have chromatin).

• Chromosomes in eukaryotic cells are composed of chromatin (DNA-protein complex).

• DNA is made up of nucleotide units which composed of phosphate, deoxyribose sugar and nitrogenous base.

• Two complementary, anti-parallel DNA strands coiled up in a helical path, in a double-helix structure.

• In protein synthesis, DNA makes RNA which makes protein. This happens via the process of transcription and translation, respectively.

• DNA replication involves the process where two DNA parental strands separate to direct enzyme-catalysed synthesis of new complementary daughter strands following the normal base-pairing A-T, G-C rule.




ON-LINE DISCUSSION

•Discuss the distinctive features of

eukaryotic chromosome.




Terima Kasih

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