topic 7 - DNA

Question 1

DNA

Answer 1

deoxyribonucleic acid

Question 2

how does DNA fit into the nucleus

Answer 2

-every human cell has 46 DNA molecules in its nucleus, 23 pairs of chromosomes
- Histones and Chromatin

Question 3

explain Histones and chromatin

Answer 3

-DNA strands are bound and wrapped around special proteins called histones (looks like a beads on string)
-the “beads on string” then coil up on themselves to form chromatin

Question 4

histones, chromatin to chromosomes

Answer 4

in cells that are about to undergo cell division (mitosis or meiosis)- the chromatin undergoes further coiling (super-coiled)
-these super coiled structures are called chromosomes

Question 5

DNA structure - Nucleotide composition

Answer 5

• DNA is polymer
• the repeating units in DNA are called nucleotides
  -each nucleotide is made up of a phosphate group, sugar group (deoxyribose) and one of four nitrogenous bases.

Question 6

name the four nitrogenous bases

Answer 6

Adenine, Thymine, Cytosine, Guanine

Question 7

DNA structure, double stranded Helix

Answer 7

helix= twisted ladder
sides of ladder:
-sugar phosphate backbone
-the 2 strands run in opposite directions

Rungs of the ladder:
-complementary bases
-A always with T - held together by 2 weak hydrogen bonds
-C always with G - held by 3 hydrogen bonds

Question 8

importance of bases

Answer 8

-the exact order of A, T, C, G in the DNA determine the genetic code

Question 9

differences of Nuclear DNA (nDNA) to Mitchondrial DNA

Answer 9

-found in nucleus
-long strands
-Bound to proteins called histones
-46 strands/chromosomes in each nucleus
-thousands of genes

Question 10

differences of mitochondrial DNA to nucleus DNA

Answer 10

-found in mitochondria
-small, circular strands
-not bound to any proteins
- 5-10 molecules per mitochondrion
- 37 genes:
24 genes for making tRNA molecules
13 genes for making enzymes that involved in cellular respirations

Question 11

1st step of DNA replication process

Answer 11

step 1- the two strands seperate
-carried out by an enzyme called helicase - unwinds the helix
-made possible due to the weak hydrogen bonds between bases
-each strand will serve as a template for a new complementary strand to be made

Question 12

2nd step of DNA replication

Answer 12

step 2-make the new complementary strand
-DNA polymerase moves along each of the template strands and makes the new strands
-it obeys the base pair rules
-the 2 new strands are made in opposite directions

Question 13

define DNA polymerase

Answer 13

an enzyme that joins nucleotides together

Question 14

role of DNA in a cell

Answer 14

DNA contains the genetic code- order of bases act as the instructions for protein synthesis

Question 15

explain protein synthesis

Answer 15

-involves joining amino acids together to make proteins
-requires ATP- is an anabolic process
-examples of proteins: hormones, enzyme

Question 16

how does your cell which amino acids, which order, and how many to use when it makes proteins?

Answer 16

each gene in your genome encodes the instructions for a particular protein
-the DNA within a gene is ‘read’ in sets of 3 (called triplets)
each triplet encodes for a specific amino acid

Question 17

define ribosomes

Answer 17

ribosomes make proteins
found in cytoplasm
they join the amino acid together to make proteins

Question 18

give brief explanation of Transcription

Answer 18

-dna is too large and important to leave the nucleus
-cell makes a copy of the gene which encodes the necessary protein
-copy is sent to cytoplasm for ribosomes to ‘read’
-this copy is made out of RNA instead of DNA
-it’s called mRNA (messenger rna)

Question 19

define Ribonucleic acid

Answer 19

-single stranded
-uses ribose instead of deoxyribose sugar in the sugar phosphate backbone
-uses uracil instead of Thymine
-not as stable-will break down over time
-not good as long term store of the genetic code

Question 20

define transcription

Answer 20

-the process of making mRNa
-the mRNA copy (which is the copy of the genetic instructions) will later be used by ribosomes to make the encoded protein
-it is smaller than dna and hence can leave the nucleus via the nuclear pores

Question 21

what does transcription require

Answer 21

RNA polymerase -makes RNA by joining nucleotides together

Helicase- are a subunit of RNA polymerase which unwind and rewind the DNA

nucleotides- A, C, U, G

energy

Question 22

explain the transcription process:

Answer 22

1. initiated by chemical messages:
   -enter the nucleus from the cytoplasm
   -bind to DNA at start of the relevant gene (region called promotor)
2. this causes RNA polymerase to also bind to the promotor.
   -the helicase parts of the RNA polymerase unwinds the DNA (about 17bp at a time) ahead of the RNA , rewinds it behind.
3. the RNA polymerase creates an RNA copy of the templates strand.
4. when the RNA polymerase reaches the terminator region (special sequence of bases)- it unbinds from the DNA and releases the mRNA transcript
5. mRNA then moves into cytoplasm via a nuclear pore

Question 23

describe the process of translation:

Answer 23

• is the production of a protein using the information coded in the mRNA transcript
• it is carried out by ribosomes
  -the ribosome looks for a particular sequence (AUG-start codon) this is where it binds and starts making the protein
• the ribosome then moves along the RNA reading it 3bp at a time. Each group of 3bp (called codon) codes for a particular amino acid

Question 24

translation requirements:

Answer 24

mRNA- the message/copy of the gene- contains instructions for the protein

-ribosome- the protein assembling machine- ribosomes themselves are made out of:
proteins
rRNA- ribosomal RNA- special kind that brings the particular amino acid needed to the ribosome

tRNA- transfer RNA- special kind of RNA that brings the particular amino acid needed to the ribosome

release factors- special proteins that bind to the STOP codons- when the ribosome reaches it will detach from the mRNA and release the protein

Question 25

tRNA

Answer 25

-responsible for brining the correct amino acid to the ribosome to incorporate into the protein

-are made out of RNA which folds itself into a clover-leaf shape

-two important parts of the tRNA:
amino acid attachment site
Anticodon- a sequence of 3 bases which will correspond to a sequence of 3 bases in the mRNA strand