DNA structure

Question 1

main steps in DNA

Answer 1

replication information transferred from one dna molecules to another
transcription infro is transferred from DNA to an RNA molecule
translation infro transferred from RNA to protein through a code that soecifies the amino acid sequemce

Question 2

But how was DNA identified as the source of genetic information??

Answer 2

Structure and role as the genetic material NOT discovered by a single person
Structure and role as the genetic material were GRADUALLY revealed over almost 100 years (and still ongoing)
Miescher isolated a novel substance from white blood cells nuclei in pus. This material was slightly acidic and high in phosphorus.
The idea that nucleic acids are the genetic material NOT widely accepted until after 1950

Question 3

The discovery of the three-dimensional structure of DNA

Answer 3

James Watson and Francis Crick
1953 Chargaff’s rules: A=T and G=C Wilkins and Franklin: X-ray diffraction images of DNA

Question 4

how much DNA does human cell have

Answer 4

Human cell => more than 6 billion base pairs of DNA => more than 2 meters!!

Question 5

How to pack DNA into a cell: Bacterial Chromosome

Answer 5

Highly folded in twisted loops

Associated with proteins (NOT histone proteins) Bacterial DNA is highly folded into a series of twisted loops

Question 6

How to pack DNA into a cell: Eukaryotic Chromosome

Answer 6

Eukaryotes have multiple, linear chromosomes in the cell nucleus and each species has a characteristic number of chromosomes
The chromosomes usually occur as 2 complementary sets = diploid
Humans have 23 pairs of homologous chromosomes; one haploid set of chromosomes from the egg and the other haploid set from the sperm.

Question 7

what is haploid

Answer 7

Sperm and egg cells have one of each chromosome - haploid

Question 8

what do centromeres display

Answer 8

Centromeres display considerable variation in their DNA sequences.

Question 8

how many pairs of chromosomes do we have

Answer 8

23 chromosome pairs, so 46 chromosomes in total
This is 22 pairs of autosomes and a pair of sex chromosomes

Question 9

The repeating unit in human Telomeres is:

Answer 9

5´-TTAGGG-3´

Question 10

DNA sequence of proteins

Answer 10

Unique-sequence DNA: once or a few times

Question 11

DNA sequence of Ribosomal RNAs (rRNAs), transfer RNAs (tRNAs), others with unknown function

Answer 11

Moderately repetitive DNA: 150 to 300bp repeated many thousands x

Question 12

DNA sequence of Centromere and Telomeres, others with unknown function

Answer 12

Highly repetitive DNA: >10bp hundreds of thousands to million copies

Question 13

Eukaryotic chromosomes: Short Tandem Repeats (STR)

Answer 13

Very short DNA sequence repeated in tandem
1 to 6bp repeat units and can extend up to 150bp
Also called microsatellite

Question 14

Is H1 part of nucleosome?

Answer 14

It binds to nucleosome but not part of it

Question 15

5 positively charged histone proteins

Answer 15

H1 H2A H2B H3 H4

Question 16

Most of the centromere and telomere structures consists of

Answer 16

Heterochromatin

Question 17

What does the term antiparallel mean

Answer 17

The strand run in opposite directions
The 5’ end of one strand is opposite to the 3’ end of the second strand

Question 18

What is the function of histone H1

Answer 18

H1 clamps the DNA joining and leaving the nucleosome to the core protein octomer
Chromosome conedenstaion by H1 binding (helps link nucleosomes together)

Question 19

What drives the formation of the 30nm fiber of chromatin structure

Answer 19

Histone protein interactions

Question 20

Genetic material must meet what requirements

Answer 20

Contain complex information
Replicate faithfully
Encode the phenotype
Have the capacity to vary

Question 21

Histones are made of what amino acids

Answer 21

Arginine and lysine which is why rich in positive charge

Question 22

What forms nucleosome

Answer 22

DNA wrapped around histone proteins

Question 23

High levels of folding

Answer 23

DNA wraps around histones forming nuclesomes Nucleosomes coil into chromatic fibre Chromatin loops and folds forms chromosomes

Question 24

What does topoisomerase do

Answer 24

An enzymes Which twist or untwist the dna Control DNA tension during replication and transcription

Question 25

What makes DNA so negatively charged

Answer 25

The phosphate group

Question 26

What uses histones and what uses non histone proteins

Answer 26

Prokaryotes use non histone proteins Eukaryotes use both histone and non histones Histones for main packaging are H1 H2A H2B H3 H4 Non histones for regulation & structure in eukaryotes are transcription factors DNA polymerase helicase and structural scaffold proteins Non histones is prokaryotes like HU IHF ETC

Question 27

DNA in prokaryotes are

Answer 27

Circular supercooled loops forms nucleoid

Question 28

Diploid

Answer 28

2n 23 pairs

Question 29

Haploid

Answer 29

n 23 chromosomes

Question 30

How many chromosomes would you expect to be present in a single human egg cell

Answer 30

23

Question 31

How many chromosomes in human white blood cell

Answer 31

46

Question 32

How many autosomes in singles human sperm cell

Answer 32

22

Question 33

Linear chromosome contains

Answer 33

Single molecule of double stranded DNA