Chapter 9: DNA & Protein Synthesis

Question 1

DNA molecule (deoxyribonucleic acid)

Answer 1

Stores genetic info that determines cell structure and function. Is in all organisms.

Question 2

Where DNA is found?

Answer 2

DNA mostly found in cell nucleus (Nuclear DNA). Some in mitochondria (mtDNA).

Question 3

DNA structure

Answer 3

DNA made of joined nucleotides forming 2 chains that twist into spirals making double helix shape
Nucleotides contains deoxyribose sugar (5 carbon sugar), phosphate group, 4 nitrogen-bases:

Question 4

4 nitrogen bases

Answer 4

• Adenine, Thymine. 2 bonds in between.
• Guanine, Cytosine. 3 bonds in between.
• All joined by weak hydrogen bond
• Order of nitrogenous bases occurring in DNA determines genetic code, 4 letters (A, T, C, G).

Question 5

Nuclear DNA

Answer 5

• DNA in nuclues, long strands wrapped around group of 8 proteins called histones forming nucleosome.
• When cell isn’t dividing: DNA forms chromatin.
• When cell is dividing: Chromatin becomes more tightly coiled forming chromosomes (46 chromosomes in humans).

Question 6

Mitochondrial DNA (mtDNA)

Answer 6

• DNA in mitochondria for mitochondria function. Mitochondrial DNA is circular molecule unbound to proteins, only inherited from mother (cuz mitochondria in sperm dissolves).
• Has 37 genes, 24 has code to make tRNA (transfer RNA) for protein synthesis. Others code to make enzymes for cellular respiration.

Question 7

DNA replication

Answer 7

DNA must produce exact copy of itself for cell divisions.

Question 8

DNA replication 1.

Answer 8

2 DNA strands are separated by helicase enzyme. Separation works because of weak hydrogen bonds in bases.

Question 9

DNA replication 2.

Answer 9

2 separated strands (requires ATP) containing half original info. Each strand is template of nucleotides for new strands.

Question 10

DNA replication 3.

Answer 10

• Replisome, large protein complex for replication contains:
  1. DNA polymerase enzyme adds new nucleotides to new strand and aligns bases (requires RNA primer). DNA polymerase works in 1 direction so there’s 1 continuous and 1 lagging strand (in sections).
  2. DNA ligase enzyme joins DNA sections together.

Question 11

DNA replication ends:

Answer 11

2 identical DNA strands, consisting of 1 new and old strand (semi-conservative).

Question 12

RNA (ribonucleic acid)

Answer 12

RNA, other main nucleic acids type (DNA) in humans. Found in cytoplasm.

Question 13

RNA difference

Answer 13

• Single chained.
• Uracil replaces thymine (cytosine, guanine, adenine, uracil).
• Ribose sugar instead deoxyribose.

Question 14

3 types of RNA

Answer 14

• mRNA (messenger): Made in nucleus and carries genetic info to cytoplasm to be read by ribosomes.
• rRNA (ribosomal): Makes up 60% of ribosomes, ensuring correct alignment between mRNA, tRNA, ribosomes.
• tRNA (transfer): Carries specific amino acid, vital for protein synthesis.

Question 15

Codons/triplets

Answer 15

DNA bases codes for protein synthesis (produce proteins). Sequence of 3 bases called triplet/codon for specific amino acid.

Question 16

Transcription

Answer 16

• Occurs in nucleus where DNA and genetic instruction are copied (transcribed) from DNA to mRNA.
• Triggered by chemical messengers that bind to particular gene (sequence of bases in DNA), causing RNA polymerase enzyme to begin making mRNA.

Question 17

Transcription 1.

Answer 17

RNA polymerase pulls DNA apart with help of helicase enzyme. Around 17 bases separated by enzyme.

Question 18

Transcription 2.

Answer 18

mRNA is made by pairing complementary bases with DNA (guanine to cytosine, adenine to thymine, uracil to adenine).

Question 19

Transcription 3.

Answer 19

Genes tells RNA polymerase to stop and mRNA pulls off.

Question 20

Translation

Answer 20

Occurs in cytoplasm. Uses information in mRNA making amino acid polypeptide.

Question 21

Translation 1.

Answer 21

mRNA travels out of nucleus. Ribosome binds to start codon (AUG) in mRNA.

Question 22

Translation 2.

Answer 22

Ribosome moves along mRNA 3 bases/codon at a time. Each 3 codon corresponding to specific amino acid.

Question 23

Translation 3.

Answer 23

tRNA recognises complementary codon and binds to active site of ribosome, leaving it’s amino acid.

Question 24

Translation 4.

Answer 24

Ribosome moves along mRNA adding more amino acid to growing chain.

Question 25

Translation 5.

Answer 25

Polypeptide is released when stop codon (UAG) is reached. Protein produced.

Question 26

Lipid & Carb synthesis

Answer 26

• No genes have instruction to produce lipids & carbohydrates, but lipids & carb synthesis requires enzymes (proteins).
• DNA in genes has code for protein production, therefore genes indirectly control lipids & carbohydrates synthesis.

Question 27

Gene expression

Answer 27

Process of copying info from DNA to mRNA, then translating amino acids to form protein. Only certain genes are transcribed in each cell. Genes are on or off depending with cell type and activity.