Molecular Biolgoy - DNA, RNA, proteins (SEMESTER 2/MCQ 3)

Question 1

What is DNA?

Answer 1

Deoxyribonucleic acid
Found in cellular structures - CHROMOSOMES

Genetic material to construct entire organism, providing its traits
Accurately copied via mitosis (identical copies)
Accounts for variations within species - each persons DNA is unique
DNA gets passed from parent to offspring - inherited

Question 2

DNA in multicellular organisms

Answer 2

Multicellular - like pants + animals, genetic material enables fertilised egg to develop into an embryo, then into a mature organism

Question 3

4 key roles of genetic material

Answer 3

1️⃣ information = to construct entire organism
2️⃣ replication = accurately copied via mitosis (identical)
3️⃣ transmission = after replication needs to be transferred from parent to offspring // cell to cell during division
4️⃣ variation = differences in DNA account for variation within each species

Question 4

What are chromosomes?

Answer 4

Unit of genetic material composed of DNA + associated proteins
Eukaryotes - chromosomes found in nuclei + plastids + mitochondria

Question 5

Griffith’s bacterial transformation - helps identify genetic material

Answer 5

Streptococcus pneumoniae:
Capsule-secreting = smooth colonial morphology cause symptoms
Non-secreting = rough colonial morphology

TRANSFORMATION principle occurred when types heat-killed s + live type r were mixed + injected into the mouse

Question 6

Avery, MacLeod + McCarty used purification methods to reveal DNA is the genetic material

Answer 6

Only purified DNA (opening cells + separating DNA via centrifugation) from type S could transform type R
If still contain traces of RNA/protein = transforming principle
Add DNase, RNase, proteases
RNase + proteases didn’t stop transformation
DNase no transformation occurred

Question 7

DNA structure

Answer 7

Nucleotides = building blocks of DNA (+RNA)
Nucleotides form strands, if 2 strands then forms a double helix
If associated with proteins forms chromosomes
Sugar-phosphate backbone
Bases inside helix - strands stabilised via hydrogen bonding
Adenine➡️Thymine (uracil if RNA) Cytosine➡️Guanine
10 bases per turn of helix
DNA strands complementary
^ known as Chargoff’s rule

Question 8

What is a genome?

Answer 8

Complete genetic composition of an organism or cell

Question 9

What are nucleotides + their structure?

Answer 9

Building blocks of the DNA + RNA strands

Structure: 
Phosphate group - negative charge 
Pentose sugar (deoxyribose = DNA // ribose = RNA)
Nitrogenous base (purines = adenine + guanine // pyrimidines = cytosine + thymine (DNA) uracil (RNA)

Question 10

Numbering system on a nucleotide

Answer 10

Sugar carbons 1 to 5
Phosphate group attached to 5
Nitrogenous bade attached to 1

Question 11

Bonding within DNA structure + nucleotides

Answer 11

Nucleotides covalently bonded - forms a strand with strongest intermolecular bonding
Phosphodiester bond - phosphate group links 2 pentose sugars to form the backbone of the strand
Hydrogen bonds between bases when there are 2 strands

Question 12

Directionality in nucleotide strands + DNA

Answer 12

5 prime to 3 prime

DNA - 2 strands, 1 will run 5 to 3 prime, but, other run in opposite direction, as DNA is anti parallel

Question 13

3 types of DNA replication

Answer 13

Semi conservative = DNA 1 parental + 1 new strand
Conservative = 1 double helix with both parental strands + other with new daughter strands
Dispersive = DNA strands where segments of new + parental DNA interspersed

New strands = daughter strands
Original strands = parental strands - template strands

Question 14

Aim of DNA replication

Answer 14

2 parental strands = templates
End result = 2 new double helices, same base sequence as original
DNA strand made in a 5 to 3 prime direction, template 3 to 5 prime

Question 15

Origin of replication
What does synthesis start with?
Direction?
Types of strands?

Answer 15

Origin of replication = replication initiated, opening made called replication bubble, forming 2 replication forks
Replication occurs near the fork
Synthesis starts with a primer (short strand of RNA)
Synthesis occurs in a 5 to 3 prime direction
Leading strand = made in direction fork is moving, synthesised as one continuous long molecule
Lagging strand = made as Okazaki fragments which are connected later

Question 16

DNA replication enzyme DNA helicase

Answer 16

Binds to DNA
Travels 5 prime to 3 prime
Using ATP to separate strand (breaking hydrogen bonds)
Move fork forward

Question 17

DNA replication enzyme DNA tropoisomerase

Answer 17

Stops additional coiling ahead of replication fork

Question 18

DNA replication enzyme single-strand bonding proteins

Answer 18

Keeps parental strands open to act as a template

Question 19

DNA replication enzyme DNA polymerase

Answer 19

Copies DNA template strand by linking cytosolic deoxynucleoiside triphosphates to form new complementary strands

Covalently links nucleotides (DNA primase)
Makes primer (short RNA) that’s removed + replaced with DNA
Only link nucleotides in 5 to 3 prime direction
Acts on 3’-OH of existing strand

Question 20

DNA replication enzyme deoxynuccleoside triphosphates

Answer 20

Free nucleotides with 3 phosphate groups

Breaks covalent bond to release pyrophosphate (2 phosphate groups) provides energy to connect adjacent nucleotides

Question 21

DNA replication is very accurate

Answer 21

Base pairing of hydrogen bonds AT / CG

DNA polymerase active site is specific + removes mismatched nucleotide pairs

Question 22

Telomeres

Answer 22

End of chromosomes
DNA polymerase unable to copy tip of DNA strand with 3 end as no place for prime to sit

If this issue wasn’t solved linear chromosomes would become progressively shorter

Question 23

Telomerase

Answer 23

Prevents shortening of chromosomes
Attaches multiple copies of repeated DNA sequences to telomeres
Providing upstream site for RNA primer
Telomere at 3 end no complementary strand = 3 prime overhang

Question 24

Telomeres and aging

Answer 24

Body cells have a life span
Senescent cells = lost capacity to divide
Correlated to shortening of telomeres
Telomerase functioning reduces with age

Inserting more active telomerase enzyme would keep them active

Question 25

Why not insert active telomerase enzyme to keep us active?

Answer 25

Increases risk of mutations and thus cancer
Cancerous cells divide uncontrollably, as prevents telomere shortening

Children have higher levels of telomerase, thus, why children have more violent cancer

Question 26

How many chromosomes are there per cell?

Answer 26

23 pairs

46 chromosomes

Question 27

Start codons in RNA + DNA

Answer 27

RNA = AUG
DNA = ATG

Question 28

What’s the function of gene expression?

Answer 28

Produce visible traits to make up the organisms phenotypes
Code for proteins
Determines cel morphology: neurones, fibroblasts

Same DNA but differ in form + function

Question 29

What is alkaptonuria?

Answer 29

Genes determine the proteins produced
Alkaptonuria -
Patients body accumulates abnormal levels of homogentisic acid

Hypothesised due to a missing enzyme

Question 30

Difference and similarity of DNA + RNA polymerase

Answer 30

Both read DNA
However…
DNA = produces DNA strand
RNA = produces RNA strand

Question 31

Generalised process of gene expression

Answer 31

DNA gene 
⬇️
Transcription 
⬇️
RNA (transcript)
⬇️
Translation 
⬇️
Protein (polypeptide)

Question 32

What is transcription?

Answer 32

Produces RNA copy of gene = mRNA

Question 33

What is translation?

Answer 33

Process of synthesising specific polypeptide on a ribosome

Question 34

What extra gene expression process do eukaryotic cells have?

Answer 34

RNA processing
Pre-mRNA processed via splicing (using spliceosome) = mature mRNA
Introns (intervening sequences) - transcribed but not translated
Exons (expressed sequences) - coding in mature mRNA

mRNA in bacteria = directly translated into proteins/polypeptides

Question 35

Gotten to transcription of s2w3

Answer 35

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