Unit 4, topic 1.1: DNA structure and replication

Question 1

DNA

Answer 1

deoxyribonucleic acid
central nucleic acid

Question 2

Structure of DNA

Answer 2

double-helix with two anti-parallel strands held together with hydrogen bonds

Ends of DNA strands are labelled 5’ and 3’, 5’ end has a terminal phosphate group and 3’ has a terminal hydroxyl group

Question 3

Role of DNA

Answer 3

Carries cell’s genetic information using 4 different hydrogen bases

Question 4

DNA in prokaryotes (bacteria)

Answer 4

DNA found as a singular circular molecule in direct contact with the cytoplasm: A bacterial chromosome

Small loops of DNA called plasmids can also be present

Is found free in the cytosol, within the nucleoid

Question 5

DNA in Eukaryotes

Answer 5

Located in the Nucleus as well as small amounts in the mitochondria and chloroplasts in plant cells

Organized into chromosomes

Question 6

Chromosomes

Answer 6

DNA in eukaryotes is organized with proteins into chromosomes containing a linear piece of DNA with two ends

necessary for packing and replication

Question 7

Eukaryotic chromosome structure

Answer 7

Made up of two chromatids

formed from the coiling of chromatin into organized structures, which appear during cell division

Question 8

Formation of chromatin

Answer 8

DNA is complexed with histone proteins to make chromatin

Question 9

Histones

Answer 9

DNA wrapped proteins which form nucleosomes: beads on a string arrangement is structure of DNA for most of cell cycle

Histones can be modified by other processes: addition of methyl, acetyl or phosphate groups to the histone tail

the type of modification dictates the tightness of the chromatin, effecting gene expression

Question 10

Genes

Answer 10

The protein coding region of DNA

Genes can only be expressed (read and translated) when DNA is unwound

Question 11

Nucleotide

Answer 11

building blocks of nucleic acid in DNA and RNA, involved in the transmission of inherited information

Question 12

Structure of a nucleotide

Answer 12

a base, a sugar and a phosphate group

Question 13

Nucleotide base role

Answer 13

Combination of bases make up DNA and RNA storage of information, later controlling cell activity

sequence of the bases provide the genetic instructions for a cell

Question 14

Types of bases

Answer 14

Pyrimidines: Thymine, Cytosine, Uracil
Purines: Guanine and Adenine

Pyrimidine always pairs with a Purine

Question 15

Pyrimidines

Answer 15

Single ringed bases:
Cytosine and thymine found in DNA, Cytosine and Uracil in RNA

Question 16

Purines

Answer 16

Doubled ringed bases
both DNA and RNA contain Adenine and Guanine

Question 17

Types of sugars found in Nucleotides

Answer 17

Deoxyribose: DNA
Ribose: RNA

Question 18

Nucleotide phosphates

Answer 18

links to neighboring sugars, creates sugar phosphate backbone of DNA structure

Question 19

Nucleotide derivatives

Answer 19

ATP and ADP+Pi
involved in cellular energy transfer

Question 20

Nucleotide formation

Answer 20

a phosphoric acid and base are chemically bonded to a sugar molecule by condensation reaction (where water is removed)

opposite is hydrolysis

Question 21

Nucleic acids

Answer 21

macromolecules (big molecules) made up of long chains of nucleotides
example: RNA, DNA

stores and transmits genetic information

Question 22

RNA

Answer 22

Ribonucleic aids
involved in reading and translating DNA information

Question 23

Structure of RNA

Answer 23

Single strand of linked nucleotides, often folded back on itself with complementary bases joined by hydrogen bonds

Question 24

Types of RNA

Answer 24

mRNA or messenger RNA, tRNA or transfer RNA, rRNA or ribosomal RNA

Question 25

mRNA or messenger RNA

Answer 25

Transcribed from DNA, carries copies of genetic instructions from DNA to ribosomes in cytoplasm where it is translated into a polypeptide chain

Question 26

tRNA or transfer RNA

Answer 26

Carries amino acids to the polypeptide chain

One end carries the genetic code in a three-nucleotide sequence called anticodon

amino acid links to the 3’ end of tRNA

Question 27

rRNA or ribosomal RNA

Answer 27

Forms ribosomes from two separate ribosomal components and assembles amino acids to the polypeptide chain

Question 28

DNA replication process (COMPLEX)

Answer 28

1. Unwinding the DNA molecule
   → unzipped at high speed by replication fork enzyme helicase
2. Making new DNA strands
   → formation of new DNA is carried out by enzyme DNA polymerase
   → Enzyme separates nucleotides using hydrolysis
   → Strand is synthesized in 5’ to 3’ direction, polymerase moving 3’ to 5’ on the strand its reading
   → Nucleotides are assembled continuously on one strand but in short fragments on the other
   → fragments are later joined
3. Rewinding DNA molecule
   → two new double-helix DNA molecules has one strand of OG and one newly synthesized
   → rewinded to standard double-helix shape

Question 29

Semi-conservative DNA replication

Answer 29

each new double-helix contains one old parent strand and one newly synthesized daughter strand

new chromosome has twice as much DNA and the two chromatids will separate during cell division to form two separate chromosomes