Bio 8 - DNA replication

Question 1

What DNA do eukaryotic cells have?

Answer 1

They contain linear DNA molecules that exist as chromosomes

Question 2

What are chromosomes?

Answer 2

Thread-like structures each made up of one long molecules of DNA

Question 3

Where are chromosomes found?

Answer 3

In the nucleus

Question 4

Why does DNA have to be wound up?

Answer 4

The DNA molecule is so long so It has to be wound up to fit in the nucleus

Question 5

What are the proteins called that DNA is wound around?

Answer 5

Histones

Question 6

Do mitochondria and chloroplasts in eukaryotic cells have their own DNA?

Answer 6

Yes

Question 7

Describe the DNA in prokaryotic cells?

Answer 7

The DNA molecules are shorter and circular than Eukaryotic and it isnt wound in histones, its condensed to fit in the cell by supercoiling

Question 8

What is a gene?

Answer 8

A sequence of DNA bases that codes for either a polypeptide or functional RNA

Question 9

What is the first stage of protein synthesis?

Answer 9

DNA Is copied into messenger RNA to make a polypeptide

Question 10

Genes that don’t code for a polypeptide code for what instead?

Answer 10

A functional RNA

Question 11

What is functional RNA?

Answer 11

RNA molecules other than mRNA which perform special tasks during protein synthesis

Question 12

What are introns?

Answer 12

Sections of polypeptides that contain sections that don’t code for amino acids

Question 13

What are exons?

Answer 13

All the bits of a gene that do code for amino acids

Question 14

When are introns removed?

Answer 14

During protein synthesis

Question 15

Why are introns removed?

Answer 15

So they don’t affect the amino acid order

Question 16

What are non-coding repeats?

Answer 16

DNA sequences that repeat over and over and don’t code for amino acids

Question 17

What are alleles?

Answer 17

A gene that can exist in more than one form

Question 18

What does uracil pair with?

Answer 18

Adenine

Question 19

What are the two types of RNA?

Answer 19

• messenger RNA (mRNA)

- transfer RNA (tRNA)

Question 20

when is mRNA made?

Answer 20

During transcription

Question 21

what is tRNA involved in?

Answer 21

translation

Question 22

What do mRNA do?

Answer 22

it carries the genetic code from the DNA to the ribosomes, where it’s used to make a protein during translation

Question 23

What is mRNA?

Answer 23

A single polynucleotide strand

Question 24

what are codons?

Answer 24

groups of three adjacent bases in mRNA

Question 25

what does tRNA do?

Answer 25

It carries the amino acids that are used to make proteins to the ribosomes.

Question 26

What is tRNA?

Answer 26

a single polynucleotide strand that’s folded into a clover shape

Question 27

What’s an anticodon?

Answer 27

a specific sequence of three bases at the end of tRNA molecules

Question 28

What are at the two ends of tRNA?

Answer 28

• an anticodon

- amino acid binidng site

Question 29

What is made in transcription?

Answer 29

An mRNA copy of a gene is made from DNA

Question 30

What is the first stage of protein synthesis?

Answer 30

transcription

Question 31

When does transcription start?

Answer 31

when RNA polymerase (an enzyme) attaches to the DNA double-helix a the beginning of a gene

Question 32

Explain transcription (8 marks)

Answer 32

1) hydrogen bonds between the two DNA strands in the gene break which separates the strands so the DNA molecule uncoils which exposes some of the bases
2) one of the strands is then used as a template to make an mRNA copy
3) RNA polymerase lines up free nucleotides alongside exposed bases on template strand. free bases attach to exposed bases. Means mRNA strands end up being a complimentary copy of DNA template
4) RNA nucleotides paired with specific bases are joined together by RNA polymerase forming mRNA molecule
5) RNA polymerase moves along the DNA separating strands assembling the mRNA strand
6) Hydrogen bonds between uncoiled strands of DNA re-form once the RNA polymerase has passed by and the strands coil back into the double helix
7) When RNA polymerase reaches particular sequence of DNA called stop codon, it stops making mRNA and detaches from the DNA
8) in eukaryotes, mRNA moves out of the nucleus through a nuclear pore and attaches to a ribosomes in the cytoplasm where the next stage of protien synthesis takes place

Question 33

Explain translation?

Answer 33

1) the mRNA attaches to a ribosome and transfer RNA molecule carries amino acids to it. ATP provides the energy needed for the bond between the amino acid and the tRNA molecule to form
2) tRNA molecule with an anticodon that’s complementary to the first codon on mRNA attaches itself to mRNA base pairing
3) a second tRNA molecule attaches to the next codon on the mRNA
4) the two amino acids attached to the tRNA molecules are joined by a peptide bond. The first tRNA molecule moves away leaving its amino acid behind
5) a third tRNA molecule binds to the next codon on the mRNA. Its amino acid binds to the first and second tRNA molecule moves away
6) this process continues producing a chain of linked amino acids until theres a stop codon on the mRNA
7) the polypeptide moves away from the ribosome and translation is complete

Question 34

What are the three words used to describe the genetic code?

Answer 34

• non-overlapping
• degenerate
• universal

Question 35

What does a non-overlapping code mean?

Answer 35

each base triplet is read in sequence, separate from the triplet before it and after it. Base triplets don’t share their bases

Question 36

What does a degenerate code mean?

Answer 36

there are more possible comibinations of triplets than there are amino acids (20 amino acids but 64 possible triplets)

Question 37

What does a universal code mean?

Answer 37

the same specific base triplets code for the same amino acids in all living things