dna & protein synthesis

Question 1

what is DNA?

Answer 1

• dna is the molecule that carries genetic information for the development & functioning of an organism
  -dna found in all living things and codes for the instructions that makes an organism

Question 1

what does DNA stand for?

Answer 1

• Deoxyribonucleic acid

Question 2

nucleotides are made up of?

Answer 2

• made up of 3 parts
• phosphate group + deoxyribose sugar + nitrogenous base

Question 3

nucleotides

Answer 3

• A= adenine, T= thymine, G= guanine, C= cytosine
• joined together by their sugar phosphate backbones
• hydrogen bonds (weak bonds) hold together the nitrogenous bases

Question 4

how genes make a protein

Answer 4

• enzyme: a protein that speeds up chemical reactions
• DNA polymerase: an enzyme that helps copy dna during cell division (mitosis) DNA -> DNA
• RNA polymerase: an enzyme that helps copy dna during protein synthesis. its converts DNA to RNA

Question 5

RNA

Answer 5

• rna uses ribose sugar instead of deoxyribose
• has 4 base pairs: instead of thymine it has uracil
• A pairs with U and G pairs with C
• single stranded and short
• RNA can leave the nucleus and travel into cytoplasm
• 3 types: mRNA, rRNA, tRNA

Question 6

two steps of protein synthesis

Answer 6

• transcription (DNA -> mRNA)
• translation (mRNA -> protein)

Question 7

what is mRNA

Answer 7

• stands for messanger RNA
• mRNA carries the instructions for one gene
• mRNA is synthesised in the the nucleus

Question 8

what is the function of mRNA

Answer 8

• its function is to make a copy of a gene and take it to a ribosome (found in cytoplasm), where amino acids are assembled to make a protein

Question 9

transcription- DNA to mRNA

Answer 9

• transcription is the first of gene expression/protein synthesis
• it is broken into three major steps
  1. initiation
  2. elongation
  3. termination

Question 10

initiation

Answer 10

• initiation is the beginning of transcription. it occurs when the enzyme RNA polymerase binds to a region of a gene called the promoter
• this signals the DNA to unwind so the enzyme can ‘read’ the bases in one of the DNA stands (known as the template strand)
• the enzyme is now ready to make a strand of mRNA and complementry sequence of bases

Question 11

elongation

Answer 11

• elongation is when complementary nucleotides are added to synthesise an mRNA strand
• RNA polymerase reads the unwound DNA strand & builds the mRNA molecule, using complementary base pairs
• adenine pairs with uracil & cytosine pairs with guanine

Question 12

termination

Answer 12

• termination is the ending of transcription, and occurs when RNA polymerase crosses a termination sequence in the gene
• the mRNA strand is complete, and it detaches from RNA

Question 13

the three steps together

Answer 13

• the mRNA strand is now ready to leave the nucleus, travel into the cytoplasm, attach a ribosome and to be translated into a protein

Question 14

first three steps of translation- mRNA to protein

Answer 14

1. the mRNA moves through the nuclear pore to the cytoplasm
2. the mRNA attaches to the ribosome. the ribosome moves along the mRNA strand, reading 3 nucleotides (condon) at a time. translation begins at the START condon.
3. transfer RNA (tRNA) molecules ferry the amino acids to the mRNA at the ribosome

Question 15

last three steps of translation- mRNA to protein

Answer 15

4. tRNA links with the ribosome and matches its anticondon of mRNA
5. a peptide bond forms between the adjoining amino acids, forming a polypeptide. The tRNA is removed to be used again
6. the protein production stops when a STOP condon is reached. the mRNA breaks away from the ribosome. STOP condons are UAA, UGA, UAG. THey aer STOP condons because they don’t code for anything

Question 16

how does the coding work?

Answer 16

• each codon codes for an amino acid
• there are 20 amino acids, so some are coded for by multiple codons

Question 17

DNA mutations (causes & how common)

Answer 17

• mutations occur at a frequency of about 1 in every billion base pairs
• everybody has about 6 mutations in their body
• mutations aren’t always seen, the affected gene may still be able to function
• muations may be: harmful, beneficial

Question 18

how does mutations impact protein synthesis?

Answer 18

• DNA affect= substitution, insertion, deletion
• mRNA copied incorrectly
• codes for wrong amino acids
• formation of incorrect protein/part of polypeptide is missing/ not functioning protein

Question 19

what are mutations

Answer 19

• mutations are changes in genetic material; changes in DNA and gene/s
• in mutations, the DNA code can have 1 or more bases: added, deleted, or exchanged

Question 20

causes of mutations

Answer 20

• mutations may occur randomly & spontaneously due to errors in DNA replication
• they may be induced by mutagens. e.g. x-ray and uv lights

Question 21

names of genetic mutations

Answer 21

• Huntingtons disease (insertion DNA mutation)
• Sickle cell anaemia (substitution DNA mutation)

Question 22

what is huntingtons disease?

Answer 22

• a progressive brain disorder that affects the central area of the brain
• movement, mood and thinking skills are affected as a consequence

Question 23

changes in DNA segment for huntingtons disease

Answer 23

• mutation involves a DNA segment of cytosine, adenine, and guanine that appears multiple times in a row
• normally CAG segment is repeated 10 to 35 times within a gene
• in people with huntingtons the segment is repeated more than 120 times

Question 24

what is sickle cell anaemia?

Answer 24

- only one amino acid changes in the haemoglobin - the haemoglobin still functions but it folds differently, changing the shape of the red blood cell - this affects the way the haemoglobin can carry oxygen

Question 25

what are some possible genetic disorders?

Answer 25

- cystic fibrosis - klinefelter (XXY) - tourette syndrome - turner syndrome - down syndrome