chapter 22 Flashcards
(35 cards)
1
Q
nucleic acids
A
- Cells in an organism are capable of replicating
- Cells possess information on how to make new cells
- Molecules responsible for such information are nucleic acids
- Found in nucleus and are acidic because of the phosphate groups
- A nucleic acid is an unbranched polymer in which the monomer units are nucleotides
2
Q
DNA
A
- Found within the cell nucleus
- Stores and transfers genetic information
- Passed from existing cells to new cells during cell division
- H in 2’- deoxyribose
- thymine
3
Q
RNA
A
- Occurs in all parts of a cell
- Primary function is the synthesis of proteins
- OH in ribose
- uracil
4
Q
components of nucleotide
A
- pentose sugar
- phosphate group
- heterocyclic base
5
Q
pyrimidine
A
thymine. cytosine and uracil
6
Q
purines
A
adenine and guanine
7
Q
DNA and RNA
A
have A, G and C
8
Q
nucleotide formation
A
- pentose sugar + nitrogenous base = nucleoside (base attaches to C1’ of sugar (B-configuration_ purines- N9 and Pyrimidine- N1)
- nucleoside + phosphate group = nucleotide (phosphate group is attached to C5’ of sugar - phosphoester linkage)
9
Q
DNA sequence
A
- Two polynucleotide strands are coiled around each other in a spiral
- Bases on each strand extend inwardly toward each other – this is the secondary structure
- They are connected by hydrogen bonds
- They run in opposite directions
- 5’-to-3’ direction
- 3’-to-5’ direction
10
Q
DNA replication
A
- The biochemical process by which DNA molecules produce exact duplicates of themselves
- The strands of DNA are used as templates - DNA polymerase ensures correct base pairing and catalyzes the formation of phosphodiester linkages
- Components of a new DNA strand
- One new DNA strand
- Daughter strand
- One old DNA strand
- Parent strand
- One new DNA strand
- multiple sites within the molecule, this enables rapid replication of large molecules
11
Q
replication fork
A
point at which the strand is constantly unwinding
12
Q
okazaki fragments
A
-lagging strand
- grows in 3’ to 5’
grows in segments in the opposite direction
-segments are connected by DNA ligase
13
Q
Step 1 of replication
A
DNA helicase causes DNA to unwind producing 2 template strands
14
Q
step 2 of replication
A
free nucleotides pair with there complementary base on template strand by hydrogen bonds
15
Q
step 3 of replication
A
DNA polymerase joins newly attached nucleotides to create one continuous strand in the 5’ to 3’
16
Q
step 4 of replication
A
the other strand is formed in small segments (okazaki fragments) in the 3’ to 5’ direction. Segments are then joined together by DNA ligase.
17
Q
chromosomes
A
- Chromosomes are formed by the interaction of newly-replicated DNA molecules with histones (special proteins)
- A chromosome is about 15% by mass DNA and 85% by mass protein
- Cells of different kinds of organisms have different numbers of chromosomes
- They occur in matched (homologous) pairs
- Example - The 46 chromosomes of a human cell constitute 23 homologous pairs
18
Q
phases of protein synthesis
A
- trancription DNA –> RNA
2. translation RNA –> Protein
19
Q
Heterogenous nuclear RNA (hnRNA)
A
formed by DNA transcription
20
Q
messenger RNA (mRNA)
A
carries instructions for protein synthesis (carries genetic information from DNA to the ribosomes)
21
Q
small nuclear RNA (snRNA)
A
facilitates the conversion of hnRNA to mRNA
22
Q
ribosomal RNA (rRNA)
A
combines with specific proteins to form ribosomes
23
Q
transfer RNA (tRNA)
A
delivers amino acids to the site for protein synthesis (translates the genetic information in mRNA into the amino acid sequence for the protein)
24
Q
ribonucleic acids: overall process
A
- In the nucleus, genetic information for protein synthesis:
- is copied from a gene in DNA.
- makes mRNA in a process called transcription.
- The mRNA molecules move out of the nucleus into the cytosol, where they bind with the ribosomes.
- The tRNA molecules convert the information in the mRNA into amino acids in a process called translation.
25
Transcription process
-First step in protein synthesis – takes place in cell nucleus
-Process in which DNA directs the synthesis of hnRNA and mRNA. ----These molecules then carry the coded information needed to make proteins.
These are the steps:
1. First – DNA “makes” mRNA and this is done in a two-step process:
DNA makes hnRNA
The hnRNA is edited to yield the desired mRNA molecule
2. Unwinding of DNA double helix to expose a sequence of bases
-Governed by RNA polymerase
-The section that is unwound is called a gene
-20,000-25,000 genes in human body
-Alignment of free ribonucleotides along an exposed DNA strand, forming new base pairs
3. RNA polymerase (enzyme) links the ribonucleotides (forms bonds)
4. Transcription ends when the RNA polymerase enzyme encounters a stop signal on the DNA template
The newly formed RNA molecule and the RNA polymerase enzyme are released
26
post- transcription processing: formation of mRNA
-Involves post-transcription processing where hnRNA ->mRNA
-Splicing: Excision of introns and joining of exons
-Exon: A gene segment that conveys codes for genetic information
-Intron: A DNA segment that does not convey genetic information. They interrupt genetic code.
-During transcription both introns and exons are transcribed
snRNA is involved, it’s the enzyme that is responsible for the editing
-Studying the function of introns is a very active area of ongoing research
27
alternative splicing
- A process of producing several different (but similar) proteins from a single gene
- Involves splicing of an hnRNA molecule with multiple exons which can be spliced in different ways to give different proteins
28
transcriptome
- All of the mRNA molecules that can be generated from the genetic material in a genome
- It is different from a genome
- Large biochemical complexity created by splice variants obtained by hnRNA
- There are 50,000 – 200,000 mRNA molecules
- There are 20,000 – 25,000 genes in the human genome
29
codon
- A three-nucleotide sequence in an mRNA molecule that codes for a specific amino acid
- 64 codons in total – 61 code for specific amino acids
- 3 of the 64 codons are termination codons – STOP codons
30
genetic code
- The assignment of the 64 mRNA codons to specific amino acids
- The base sequence in mRNA determines the amino acid sequence for the protein synthesized.
- The sequence of an mRNA molecule involves 4 different bases - A, C, G, and U
31
characteristics of the genetic code
- The genetic code is highly degenerate
- Many amino acids are designated by more than one codon
- Met and Trp possess a single codon
- There is a pattern to the arrangement of synonyms in the genetic code table
- Proline: CCU, CCC, CCA, CCG
- All synonyms for an amino acid fall within a single category unless there are more than four synonyms
- The genetic code is almost universal
- An initiation codon exists
- Suggested by the existence of “stop” codons (STOP: UAG, UAA, UGA)
- AUG is an initiator of protein synthesis
32
codon carriers
tRNA molecules act as intermediaries to deliver amino acids to mRNA
33
anticodon
does not code for genetic information, its the complementary strand to the codon replacing T with U
34
translation
- The process in which mRNA codons are deciphered and a specific protein molecule is synthesized
- We need mRNA, tRNA, amino acids, ribosomes and enzymes
35
ribosome
- An rRNA–protein complex that is the site for the translation phase of protein synthesis
- Characteristics of ribosome structures
1. They contain four rRNA molecules and 80 proteins in two subunits
2. Each subunit possesses 65% rRNA and 35% protein
3. The active site is located in the ribosomal subunit – proteins are synthesized here adding one amino acid at a time
4. rRNA is the active site (not the protein part)
5. The ribosome is thought to be an RNA ribozyme
6. The mRNA binds to the small subunit of the ribosome
