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The DNA in a bacterial virus – enormous condensation is needed for the virus head to accomodate all its DNA. In Escherichia coli the DNA is about 1 med mer long, while the cell is close to 1 μ m. Here the DNA information also has to be read!.

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Presentation Transcript
slide1

The DNA in a bacterial virus – enormous condensation is needed for the virus

head to accomodate all its DNA.

slide2

In Escherichia coli the DNA is about 1 med mer long, while the cell is

close to 1 μm. Here the DNA information also has to be read!

slide3

In human cells the total length of the DNA is around

1 m! This requires very ”advanced” methods of

packaging to both have enough space in the nucleus

and at the same time allow reading of the information

slide5

DNA in eukaryotes (but not in bacteria and Archae) is twisted around protein

complexes called histones. They are positively charged proteins that interact

with the negatively charged DNA. Each ”ball” is called a nucleosome.

slide10

A gene is the same as a segment of DNA that after transcription and translation gives rise to a specific protein (polypeptide chain). You may also see the word cistron used. It is in practice the same as gene.

slide13

Initiation of transcription

in E. coli. The process is

much more complex

in eukaryotes in that

many accessory

proteins are involved

slide18

The DNA elements required for transcription in prokaryotes. An UP element

may or may not be present

slide19

The transcript has the same sequence as the non-template strand except that

T is substituted by U.

slide20

There are many transcription factors in bacteria, and the numbers vary a lot

between species. In eukaryotes there are an enormous number of such factors.

slide21

Several genes can be transcribed as a unit in bacteria. This is not common in

eukaryotes. Such a unit (cluster of cotranscribed genes) is called an operon.

slide22

Transcription in eukaryotes is much more complex than in bacteria, partly

because many more protein factors are involved

slide23

Transcripts in eukaryotes are heavily modified after transcription, by capping,

polyadenylation and splicing

slide24

Eukaryotic genes are made up of exons and introns. Only the exon parts

encodes the corresponding protein

slide25

Splicing may occur in different ways, so that several different proteins are made

from one specific mRNA. The varying processes may takwe place in different

tissues of a body.

slide26

Introns are spliced ourt by autocatalysis or protein-assisted catalysis. NB! This

shows that RNA alone can be catalytic (acts like an enzyme).