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Biology Exam > Molecular genetics > Flashcards

Molecular genetics Flashcards

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AP® Biology flashcards Biology 101 flashcards
1
Q

What does DNA consist of?

A

DNA is a polynucleotide

Each nucleotide consists of:
-a nitrogen base (adenine, guanine, cytosine, or thymine)
-a pentose sugar (deoxyribose)
-a phosphate

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2
Q

What does 5 prime and 3 prime mean

A

5 prime: the 5th carbon of each sugar has a phosphate group attached

3 prime: the 3rd carbon of each sugar has a hydroxyl group attached

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3
Q

What are the difference between DNA and RNA

A

-DNA-
sugar: deoxyribose
bases: GCAT
length and shape: double-stranded, long
location: nucleus

-RNA-
sugar: ribose
bases: GCAU (uracil)
length and shape: single-stranded, short
location: nucleus, cytoplasm

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4
Q

What are genes?

A

coding regions on DNA
–> determines phenotypical characteristics of an organism

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5
Q

What is a mutation? How is it caused?

A

an alteration in the DNA sequence
–> may be caused by chemical agents, ultraviolet radiation, or natural causes, can also occur during the process of DNA replication

e.g. dyes, tobacco smoke, UV rays, X rays, benzene, viruses (ex. HPV)

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6
Q

What are telomeres?

A

-are repetitive sequences of DNA at the ends of chromosomes
-prevent the loss of genetic information during DNA replication

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7
Q

What are the three steps of DNA replication?

A

Initiation, elongation, termination

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8
Q

What is Initiation? And what enzymes are involved with it?

A

a step in DNA replication
-separating the two strands
-creates a replication bubble with two replication forks

Enzymes Involved: DNA Gyrase, DNA helicase, ssB’s

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9
Q

What is DNA gyrase? and what step is it in?

A

In step 1, Initiation
-helps unwind the DNA by relieving the tension in the double helix

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10
Q

What is DNA helicase? and what step is it in?

A

In step 1, Initiation
-unwinds DNA by breaking the H-bonds between the strands

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11
Q

What are ssB’s, and what step are they in?

A

In step 1, Initiation
-single-stranded binding proteins keep strands from re-annealing (re-binding)

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12
Q

What is RNA primase? and what step is it in?

A

In step 2, Elongation
-anneals the RNA-primer to the exposed 3’ end of the replication fork

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13
Q

what is RNA primer? and what step is it in?

A

In step 2, Elongation
-10-60 base strand of RNA that serves as a starting point for DNA synthesis

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14
Q

What is DNA polymerase III? and what step is it in?

A

In step 2, Elongation
-Adds complementary bases in the 5’ to 3’ direction
-the energy released by removing 2 phosphate groups allows the bonding
-the strand that is copied continuously (5’ to 3’) towards the replication fork is called the leading strand

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15
Q

What is elongation?

A

the second step of DNA replication
-building complementary strands

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16
Q

What are the differences between the leading and lagging strand?

A

-Leading strand is being replicated towards the fork, and the lagging strand is being replicated away from the fork

-Leading strand is being replicated continuously, while lagging strand is being replicated in discontinuous fragments

17
Q

What are Okazaki fragments? and what step are they in?

A

In step 2, Elongation
-DNA polymerase III only moves 5’ to 3’ so the lagging strand is built discontinuously (in short segments) –> that is what okazaki fragments are!

18
Q

What is DNA polymerase I? and what step is it in?

A

In step 2, elongation
-removes the RNA primers and replaces the primers with appropriate DNA bases

19
Q

What is DNA ligase? and what step is it in?

A

In step 2, elongation
-attaches Okazaki fragments by creating phosphodiester bonds between sugars and phosphates

20
Q

What is Termination? And what is involved in it?

A

the third and last step of DNA replication
-completion of process

DNA polymerase II

21
Q

What is DNA polymerase II, and what step is it in?

A

In step 3, Termination
-proofreads the newly synthesized DNA and fixes incorrect nucleotides
-after proofreading, termination occurs when the two new DNA molecules separate from each other

22
Q

What are the steps in making mRNA?

A

Initiation, Elongation, Termination, Post-transcriptional modifications

23
Q

What is involved in Initiation (mRNA)?

A

-RNA polymerase binds to a specific region of the DNA, upstream of the gene to be transcribed (called the promoter)
-The DNA is unwound and the two strands are separated

24
Q

What is involved in Elongation (mRNA)?

A

-only 3’ to 5’ strand is copied (called the template strand)
-the unused strand (5’ to 3’) is called the coding strand
-free floating nucleotides are H-bonded to their complementary bases by RNA polymerase (2 phosphates are removed to create a bond)
-RNA polymerase moves along the DNA (in the 5’ to 3’ direction), unwinding and separating as it goes while the DNA winds back up behind it
-the mRNA hands free of the side of the DNA strand attached only at a few base pairs

25
Q

What is involved in termination (mRNA)?

A

-RNA polymerase encounters a sequence of bases at the end of the gene called a terminator sequence
-RNA polymerase and primary transcript are released from the DNA

26
Q

What is involved in the post transcriptional modifications of mRNA?

A

-a 5’ cap is added to the mRNA to protect it from cytoplasmic enzymes
-a poly-A tail of ~200 adenines is added by poly-A-Polymerase to the 3’ end
-capping and tailing results in the mRNA transcript being ready for release from the nucleus
-spliceosomes remove all the non-coding regions (introns) and join the coding regions (exons) to form the mature mRNA transcript

27
Q

What are the different steps of translation?

A

Step 1. The mRNA code, Step 2. the ribosomes, step 3. The tRNA, Step 4. Elongation of the Polypeptide Chain

28
Q

Describe the first step of translation, the mRNA code

A

-the message on mRNA is written in 3-letter triplets called codons
-all proteins must start with AUG (methionine) as the start codon; this may be removed later
-there is no amino acid that is coded by UAA, UAG, or UGA, and so the protein breaks here

29
Q

Describe the second step of translation, the ribosomes

A

-ribosomes are composed of ribosomal RNA (rRNA) and protein
-the 5’ (cap region) of mRNA adheres to the active ribosome
-the ribosomes will move the mRNA through it starting at the 5’ end and going towards the 3’ end

30
Q

Describe the third step of translation, the tRNA

A

-each tRNA has a cross like structure
-at the base there is an anticodon which is the complement of the codon on the mRNA
-at the 3’ end of the tRNA is the acceptor site that holds the amino acid
-1 ATP is required to attach each amino acid to correct tRNA to make aminoacyl-tRNA
-enzymes join amino acids to tRNA

31
Q

Describe the fourth and last step of translation, the elongation of the polypeptide chain

A

-the ribosomes moves the mRNA until the AUG codon fits into the P site (peptide site)
-any bases before the AUG codon are simply ignored
-amino-acyl tRNA brings methionine to the P site
-a peptide bond forms between the methionine and the second amino acid
-the process is repeated until the ribosome reaches a stop codon for which no tRNA exists
-a protein (release factor) allows the polypeptide chain to be released from the ribosome

32
Q

Name each type of point mutation

A

Substitution, deletion, addition/insertion

33
Q

What are the different types of mutation

A

silent mutation: nothing is affected as amino acid stays the same

missense mutation: amino acid is changed, thereby changing the purpose of the protein/coding of it

Nonsense mutation: When a stop codon is created, causing the protein to change/stop being created

framseshift mutation: substitution of many different amino acids or can create or remove a stop codon (basically big change)

34
Q

What are the different types of chromosomal mutations?

A

translocation, inversion, duplication, deletion

35
Q

Why is the top of the gel in electrophoresis negatively charged, and the bottom positively charged?

A

-DNA is negatively charged, thereby the DNA would be repelled by the negative charge at the top and travel to the bottom

36
Q

Why do DNA fragments get shorter as the move along the gel

A

The smallest DNA fragments can continue through the gel, while the largest ones are too big to continue further

Biology Exam (3 decks)

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