Chromosome structure

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each human cells contains how much dna

~2m and it must be packed to fit in nucleus, avoid damage

packing of eukaryotic c'some does what over time

"it varies over time
duringmitosis and meiosis it is very tightly packed and during interphase it is less packed

the c'somemust be packed to seperate
""  "" uncondensed to allow acess of enzymes to do replication and transcription (making of RNA)"

packing of eukaryotic c'somes varies over 

space and time

two types of chromatin

euchromatin
heterochromatin

chromatin is 

makes up eukaryotic chromosomes Histone proteins, bind to DNA, keep it packed

euchromatin

condenses during cell division,otherwise lightly packed

heterochromatin

stays condensed in interphase
centromeres
telomeres
most of Y c'some
barr body

histones

most abundant protiens in chromatin

the positive charge attracts the negative charge DNA

 that help package and organize DNA into a compact, structured form inside the nucleus of eukaryotic cells.

multiple types of histones combine to form 

nucleosome

nucleosome

is the basic unit of DNA packaging in eukaryotic cells. Think of it like a spool of thread—DNA is the thread, and the nucleosome is the spool it wraps around.

2 each of histone protiens H2A,H2B,H3,H4

DNA wraps around it

what is H1

it clamps DNA on its called a cromatosome

cromatosome

H1 clamps DNA on

DNase 

cuts DNA unless the DNA is bound by protien

transcriptionally active genes

less tightly bound to histones…and the histones do not bound to each other 

open chromatin configuration

"histones not bound to each other

In an open chromatin state, the DNA is less tightly wrapped around histones and more ""accessible.""

This configuration allows transcription factors and RNA polymerase to reach the DNA, meaning genes can be easily turned on or expressed.

"

closed chromatin configuration

tightly packed chromatin, where the DNA is wrapped tightly around histone proteins and is less accessible to transcription machinery.

Deacetylation

1.increases spacing between nucleosome
2.decreases histone's posotive charge

results: DNA is available for use

diffrent organisms genomes 

have  very diffrent amounts of DNA

C values

refers to the amount of DNA in a haploid genome

more tehn 50 percent of the our genomes is 

much of our DNA is repetitive
-gene famalies
-moderatley repeptive DNA
   -rRNAs and tRNAs
   -transposons
-highly repetitive DNA

Gene family

duplications results in similar genes

Moderatley repetitive DNA

hundreds to thousands of copies examples DNA encoding rRNAs,tRNAs and transposons

rRNAs

forms part of ribosome

tRNAs

transfer RNA carry to the ribosome

transposons

spequences that replicate themselves,spreads through genome 
some still replicate and others degraded
this is 45 percent of genome

 What are SINEs?

Non-autonomous retrotransposons that are short (~100–400 base pairs) and depend on LINEs for movement.

How do SINEs move?

Copy-and-paste mechanism via RNA, but they use LINE-1’s enzymes (reverse transcriptase + endonuclease).

Do SINEs code for proteins?

No, they don’t code for any functional proteins.

What are Alu elements?

The most abundant type of SINE in the human genome 10  percent of human genome less then 500 bais pairs

They rely on LINE-1 machinery to transpose.

What are LINEs?

Autonomous retrotransposons that are longer than SINEs and can move on their own.Copy-and-paste via an RNA intermediate; they encode the enzymes needed for their own transposition.About 17 percent of human genome and it codes for protiens

LINE-1

The only currently active LINE in the human genome.It helps SINEs like Alu move, and its activity can lead to mutations or genomic changes.

hifhly repetivite DNA 

are oftne below 10 base pairs
they are rarely transcribed,function mostly unknwon
telomeres
centromeres

telomeres and repition

extra copies added to ends of c'some to protect

centromeres and repition

important but now well understood