DNA replication?

when and where does DNA replication happen?

where -in the nuclues of a eukaryotic cell

when - interphase

difference between eukaryotes and prokaryotes

eukaryotes

-multicellular organism

-membrane bound

plant or animals

prokaryotes

-unicellular organisms

-not membrane bound

-bacteria

what enzyme is responsible for unzipping dna helix?

helicase - Breaks hydrogen bonds between base pairs

In what directions are nucelotides added during replication?

New nucleotides are added in the 5′ → 3′ direction.

👉 DNA polymerase can only add to the 3′ end of the growing strand

what enzyme bonds nucleotides together

DNA polymerase

👉 Adds complementary nucleotides
👉 Forms bonds in the new strand

⚠ If they specifically mean joining fragments on lagging strand:
👉 That enzyme is DNA ligase

Which enzyme is responsible for creating the covalent bonds (specifically phosphodiester bonds) that connect the sugar-phosphate backbone of the new DNA molecules?

DNA ligase is the enzyme responsible for forming covalent (phosphodiester) bonds that connect the sugar-phosphate backbone of newly synthesized DNA, especially joining Okazaki fragments on the lagging strand.

• DNA polymerase → adds nucleotides during synthesis

• DNA ligase → seals the backbone (forms phosphodiester bonds between fragments)

Describe the origin of each strand of the new double helices created after DNA replication?

• Each new DNA molecule contains:

  • One original (parental) strand

  • One newly synthesized strand

• This is called semi-conservative replication

• Ensures genetic information is copied accurately

Why do you think DNA replication important to the growth and development of a multi-cellular

• Allows cell division (mitosis)

• Ensures each new cell gets identical DNA

• Supports:

  • Growth

  • Development

  • Tissue repair

• Maintains genetic continuity

what would happen if DNA replication occured inncorectly?

If replication occurs incorrectly

• Leads to mutations (changes in DNA sequence)

• May cause:

  • Faulty proteins

  • Disrupted cell function

• Can result in:

  • Genetic disorders

  • Diseases like cancer

what is the function of primase

creates a primer that tells DNA polymerase where to build

what is the function of SSB protiens

makes sure DNA strands dont rejoin when split by helicase

what is the function of toppisomerase

• Prevents supercoiling (tension ahead of the fork)

• Works in front of helicase

• Cuts and rejoins DNA to relieve stress

Supercoiling is when DNA becomes over-twisted (tightly wound) on itself.

what are okizaki fragments?

because DNA polymerase can only build in the 5’ to 3’ direction its slower on the new strand creating a lagging and leading strand which makes spaces in between known as okizaki fragments ligase later joins these fragments

what does it mean by DNA strands are antiparrelal

Antiparallel means the two strands of DNA run in opposite directions.

5’-3’

3’-5’

what did miesher discover?

meicher discovered DNA called it nuclien at that time

what did hershy and chase discover?

they discovered DNA carries genetic information

what did watson and crick discover?

proposed double helix model?

name the purines

double ring nitrogenous bases - adenine and guanine

name the pyramidines

single ring nitrogenous bases - uracil,thymine,cytosine

explain the meaning behind 5’ end and 3’ end in DNA

5’ end - phosphate group attached to 5 carbon of first sugar

3’ end - OH group on 3 carbon of the last sugar because new nucleotides attach to this direction

what did mendel discover?

genes determine traits

garrod discovered

mutations cause inhereted diseases

ingram discoverd?

single amino acid mutation causes sickle cell anemia

what is the triple codon hypothesis explain why this number

there are 20 amino acids with 4 possible base pairs

if there were 2 codons

4² = 16 possibilities which is short of 20 amino acids

4³ = 64 possibilities with 3 codons you can code for more than 20 amino acids while also leaving space for stop/start codons

what did crick discover?

confirmed the triple codon hypothesis

how are okizaki fragments made?

How Okazaki fragments form

1. DNA unwinds at the replication fork

2. Primase lays down RNA primers

3. DNA polymerase builds a short DNA section (5′ → 3′)

4. Fork moves again → new primer added

5. More short DNA pieces are made

These short pieces = Okazaki fragments